See my reply in Boldface.

That is exactly what i'm saying because it's exactly how it works. When the siphon pump fails to work it's 90% chance it's because the main fuel pump failed so it really doesn't matter that the dying fuel pump overheats on it's last time out. What exactly is supposed to be the 'backup solution' for the fuel pump wearing out at end-of-life?


I never said that was an untrue statement, it's just that it's a practical impossibility since you have to be to -10 miles distance to empty on an x5 before the fuel pump is exposed.

you exactly opposite missed the point of that analogy, i WAS SAYING IT IS BAD to put air in before checking the pressure. That is exactly the same as putting gas in before ensuring that your siphon pump is working. By prematurely filling the tank on an x5, you are for 100% certain setting yourself up for failure. You will be inadvertently nursing along a failed fuel pump that can not do the complete job and you will absolutely 'run out of gas' with on the order of a quarter tank of gas.

fact: all fuel pumps wear out and die.
fact: most of the time as the brushes wear out they get weak before the go kaput 100%
fact: x5 will fuel starve with gas left in the tank under those conditions
fact: NOT running the tank below quarter tank will MASK a soft-fail fuel pump.


Again you have misunderstood exactly 180° opposite the entire point of my postings. I was stranded specifically because of the BAD HABIT of my WIFE of refueling prematurely. Had she even as much as told me that the time my father brought her gas, that the car showed 47 miles distance to empty when it happened I would have fixed her siphon pump/ main fuel pump problem. she was brainwashed to think it was a good/necessary thing to keep more than a quarter tank and it masked that her fuel pump was shot. I got stranded twice because she also had a bad cam shaft sensor which i fixed first completely unaware of the bad fuel pump because she out of ignorance kept filling the tank too soon. Had she properly run the tank down occasionally i'd have found the problem IN THE DAMN SUMMER not when it was ZERO DEGREES, I'm posting to inform the open-minded public who may just not want to be stuck at the side of freeway at 11pm at 6 degrees. because somebody ignorantly misled them to think there was some benefit from prematurely refueling their car.

I *only* got stranded *only* because my *misinformed wife* was *ignorantly* prematurely refueling her car at a quarter of a tank.

If she did not follow this ignorant practice i'd have known about the problem 9 months ago in SUMMER when the pump first failed, not at 11pm on the first cold day of the year when no tow trucks were available. You don't have control over when a part fails, but with the soft-fail nature of a fuel pump and the way the siphon jet works, you have a good 'cushion'; that is to say; if you 'run out of gas' and there is a quarter of a tank on the gauge, it's at least 90% chance the main fuel pump has failed and you can get home all the way across the country under such conditions you just have to prematurely refill at a quarter tank.

I got stranded because I had two failures, and specifically because of the ignorant refuel at quarter tank i was completely unaware of the fuel pump situation. I replaced the camshaft position sensor and because I had put in 2 gallons of gas to try to start the car, that was enough to AGAIN mask the fact the fuel pump was shot.

You can 'keep on guessing' but you aren't making a lot of sense trying to pull 1950s myths into the 21st century they do not apply in any way shape or form to the x5.


You can't back that up at all; that is absolute suposition, in-fact you are again just proving my point; if the OP was correct (not probable, no evidence), The pump when it finally died 'kind of exploded' and left the shrapnel in the tank. That has zero bearing on how it got there and you still don't seem to get the point that the x5 will not expose the pump to air until you are below 0.0 gallons of gas. In other words you quarter tank to keep pump covered concept applies but the numbers are wrong, in order to keep the x5 fuel pump covered, it's quite important that you keep the tank full above 0.0 gallons, they do mention in the manual.

No telling if the original owner who put on 90% of the miles followed the ignorant concept of stopping for gas when you shouldn't, but the pump life is not extended one revolution on an x5 by adding extra gas when it's not needed, not one single revolution. I laid out exactly why the opposite is more likely true; you are presenting yourself to 33% increase in the odds of getting polluted gas or debris in the tank by subjecting yourself to that many more refills.

You are also dramatically reducing the utility of the vehicle by dropping the range by a tremendous amount; from as high as over 500 miles to maybe 350 miles, that's just plain ignorant for no fact-based reason.

You just argued my point for me, not sure you noticed. You literally just said you do not have to refill a tank at a quarter of a tank because the pump is now electric. That is of course one of the inputs into why it makes no sense.

I am only speaking exclusively of the x5 who's gas tank is designed with an 'extra 2 gallons' not shown on the fuel gauge so that when you drive the car right down to empty (0 miles DTE), there is actually about 1.5 to 2.0 gallons of gas that is keeping the fuel pump submerged and the car quite drivable for another 15-20 miles as evidenced by one of the posters who said he regularly drives his x5 to the 10 to 15 miles past empty zone.

I'm not exactly sure what is your point of trying to disprove simple facts that i have discovered about how the x5 fuel supply system works. I did the most extensive research and found out that the majority of postings about the fuel supply system on the x5 were not correct and in many cases exactly opposite of correct, so i posted an exhaustively detailed message of exactly how it works.

if you have any actual fact-based data to share to counter any of my claims please do so, but mysticism, conjecture, supposition will not help anybody.

She won't fill up due to mythical reasons anymore no, she will likely fill up at an eighth of a tank rather than waiting for the low fuel light just for lack of concern of will a gas station be there when needed.

I believe facts, straight up; you seem to think that adding gas to an x5 at any time before the low fuel light comes on is helpful to the well being of the car and that is simply not true. My entire effort of replying to your posts is to specifically avoid you misleading other people with misinformation about that key element.

To be perfectly clear once more: from the CAR's perspective, there is absolutely no difference between having 8 gallons of gas and 0 indicated gallons of gas in the tank.

You made numerous incorrect assessments based on my statements which I will clear up for other readers that may have been misled:

Not an accurate statement; my siphon pump was not working full power because of a leak, it also was not working full power because the main fuel pump had 'soft failed' (worn out brushes/commutator) was reducing it's power output.

It's called a 'soft failed' fuel pump. it has lost power due to wearing out and is the most common form of fuel pump failure by far. At the end-of-life more likely than any other failure mode, the fuel pump will output less and less power until you have negative symptoms; in most cars that means loss of power at WOT (wide open throttle) in the case of bmw's that have a siphon jet fuel pump, the symptom is running out of gas when the gauge reads more than zero.

You did; you keep claiming that you need to have more than 2 gallons of gas in an x5 to ensure the fuel pump is cooled, that concept is based on a '1950s' myth that the fuel pump won't be properly covered in gas unless there is a quarter tank of gas; that is a myth.

Define 'down to empty' Yes, if you run the car down until you sputter to a stop while the fuel supply system is functional, you can expect damage to your car. The consumer report concept straight-up does not apply to an x5 at all; where most cars have a more or less uniform shape to their gas tank where even going up or down a hill will 'fuel starve' the pump, the x5's fuel supply system is eon's ahead of that design and will supply fuel to the engine and keep the pump properly submerged down to approximately 1 gallon of gas remaining (which is AFTER the needle is down to 0.0 gallons); there is 8L reserve in the 6 cylinder models and 10L reserve in the 8 cylinder models.

I've never disagreed with the concept is is bad to run a fuel tank 'down to zero', that is bad in many ways, my argument is that it has no beneficial benefit to the engine to refuel an x5 before the low fuel light comes on, not one single thing.

The crud the OP mentioned was diagnosed as shrapnel from the pump when it died, that has absolutely no bearing on how it got there. There is no way to use it to argue for or against premature refueling, other than to say, it really has no factor in the 'refuel early' argument; fuel pumps suck the fuel from the VERY BOTTOM of the tank, if there is any 'crud' in the tank it's going to be the first thing out of the tank if it's density is higher than petrol.

And your point is?

Find me a study showing that an x5's fuel pump will last longer over it's life, I'll pay for your premier membership to xoutpost. There is no study because the cars are very much designed to use every drop of fuel shown by the gauge, right down to 0.0. The x5 has plenty of gas in the reserve tank that will keep the 'crud ratio' down and the pump quite securely cooled.

Now i'm confused, i'm talking about not letting the tank get LOW; you are talking about not letting it get HIGH?

That's a very logical argument that would work very well in concert with draining the car down to low-fuel; if you don't drive the car much it would be best to only put in the amount you think you'll use in the next few months since gas does 'geo bad' especially the crappy gas available in the midwest; drain that crap right down to empty and put in some good fuel, half a tank, quarter a tank whatever you need.

That is only PART of your comment; you said that it was bad to run a tank lower than a quarter of a tank, because that would not allow proper cooling of the fuel pump.

Nobody will disagree with it's not a good idea to run a tank dry. running a bmw x5 to 0.0 on the gauge will not cause this problem as bmw wisely designed the system with an 'extra couple of gallons' to keep the pump under fuel, even at the empty line on the gauge and even at a rather steep angle as in a hill for example.

This is not an accurate statement at all, that is the problem, you have a conceptual error in how the bmw x5 fuel supply system works, just as in virtually every post i read in the 20 or so hours of discovery before writing the beat-all-end-all description of exactly how the system works.

The primary electric fuel pump is the 'heart' of the system and in the vast majority of all fuel supply problems will be the cause, probably at least 80% of the time.

The reason that adding some fuel to the tank helps get a car started when this happens is NOT LIKELY AT ALL that the transfer pump has failed. In most cases, the main pump has soft-failed and is not supplying enough excess volume to get the 1 to 1.3 bar of pressure incoming into the jet pump.

You will see a wide variation of how many miles to empty where people stall and that is for a very simple reason: the main pump is still supplying pressure just not enough, the depth of the fuel on the left side of the tank supplies SOME of the pressure head at the pump foot (feet), so for example one might starve the engine at 50 miles to go, some 100, some 20…

In my case, I had the wonderful combination of BOTH the main pump AND the siphon pump had a failure.

The siphon pump o-ring issue probably took 30-40 miles off the distance to empty and i would stall if i tried to get below 30-40 miles, The main pump soft-fail took another 40 or so miles off the distance to empty by suppling a weakening pressure and volume into the jet pumps; combined it would starve the engine at about 70-80 miles distance to empty.

I fixed the main pump first since that is the most-likely candidate of causing the symptom of running out of gas when there is fuel indicated on the gauge.

I was not happy with the value of fuel in the right tank, so i did more digging and found in-addition the leak on the siphon jet.

With the new pump i probably could have gotten down to 10 miles distance to empty, possibly even down to zero, since i don't know how bad the leak was at the o-ring though it was completely out of the groove in one spot so it had to be pretty significant of a leak.

and to review:

I'm not saying you are 'wrong' to have a phobia about running a tank on an x5 below a quarter of a tank any more than it's wrong for somebody to have fear of heights, i'm just pointing out 'just the facts' and that there is no reason based on logic that will bring somebody to the conclusion that a fuel pump will last longer if you do so.

I was stranded on the freeway when it was single digits TWICE entirely because my wife has a phobia that it's not good to have less than a quarter of a tank of gas in the car. I don't fight her on it for the simple reason that it is good to have enough gas to deal with unplanned situations like being stuck on a freeway for hours because of an accident. I never said it's bad to have spare gas in the tank, I'm just 'on a mission' to get people to properly exercise their fuel system regularly to make sure it's working.

The problem with this is; if you NEVER run the tank down to 'lights on empty', you will be masking the eventual failure of the fuel pump, it's completely false security, you will have your 'just in case' quarter of a tank that is supposed to save your butt and it will leave you hanging, as happened to me TWICE

I'm ok with ME being the one to take the risk of discovering that the main fuel pump has 'soft failed' and do that 'drive to empty' (possibly with a gas can in the trunk), but it's the only way to ensure the fuel system is still operating properly. even if you were to take pressures at all the right places, you won't know if none of the 9 or 12 parts that all have to be working properly are working properly unless you periodically drive your gas tank down to empty.

I've driven my x5 down to single digits about 3 times in 23,000 miles or so, you don't have to do it 'every time' you just should do it a couple of times per year (preferably in the summer when you won't die from exposure if you get stuck somewhere).

@ upalinght. This whole 'back and forth' only has to do with one thing; you said that you can or will damage the x5's fuel pump if you regularly run the gas tank down lower than a quarter tank (i am paraphrasing); This is an absolutely false statement that can't be backed by any science. If i 'heard you wrong' straighten me out; If you had said what you said in this latest exchange "it is very bad to run the car OUT OF FUEL", i would be on board with that statement completely, bad, very bad, in many ways including bad for the fuel pump.

There are plenty of very good reasons to keep at least a quarter of a tank of gas in the car, such as mentioned above, they are just 100% related to the PEOPLE in the car and have 0% to do with the car.

See my reply in boldface.

This exact same argument is happening in my Volvo forum 😂 Although you guys are keeping it a bit more civil 👍

Sent from my SM-G900F using Tapatalk

Your 'best reason' is false sense of security and is the main reason i've been posting the replies.

I was stuck on the side of the road for the same exact reason eventually YOU will be with HALF or a FULL tank of gas.

You will wear through the 'soft fail' zone of your fuel pump, since it will be masked by premature refueling and it will die completely, just as a recent post to xoutpost where the guy got towed to a gas station and refilled to the top and it wouldn't start because the pump was completely dead.

It doesn't matter if you were correct the whole time and premature refueling added lifespan, it is inevitable it will fail; fuel pumps last 4000-6000 hours on average.

If you follow the practice of refuel before the siphon jet does its job and empties the left side of the tank, you will never know the main pump has 'soft failed'. It will 'hard fail' and you won't get home with a can of gas, you'll need a tow and the main pump will need to be replaced before the car will operate.

My reasoning will get you home with a can of gas,

Your reasoning requires a tow and an emergency replacement of the main fuel pump.

I'm not sure why it's so hard to understand this concept.

To answer your questions,

Yes I did perform a test and mentioned several times.

At the particular depth of fuel on the left side of the tank, When the main pump was 'soft failed' and the o-ring was leaking, The right side test 6 only held 0.9L of gas, meaning the surge tank was no longer being kept full. When i replaced the main pump, that number went up to 1.1L of gas, clearly a difference but it wasn't being kept full to overflowing; i could take a hard left turn and slosh some gas into the surge tank, but after a minute or three, the level would even out at 1.1L again. What you missed was the 'leaking like a sieve' non-o-ring was from the connection that is not designed to be taken apart, and likely not part of the original equation of me getting stranded, i never got a reading of how bad it was when that was leaking, it would have been worse than when i started, it surely leaked more than the o-ring leak.

I may have 'put words in your mouth' about exactly how you said to keep a quarter of a tank. You said in separate statements that; ➀ you always keep a quarter tank of gas and that ➁ consumer reports said if you let your gas get too low it will wear the fuel pump. The 'take away' from those statements is that you decided based on things such as consumer reports that 'the appropriate amount of not too low' is a quarter tank. Based on your actions that is established fact. There may be other reasons also but the argument here is: is there any logical reason to put gas into an x-five from the engine's well being before the low-fuel light comes on. the answer is no, plain and simple. For the well-being of the occupants, you can come up with many reasons, i'm not arguing that point at all.

I don't want other people to get stuck on the side of the road as happened to me because of other people following the rule my wife did of prematurely refilling their tank always.

It is perfectly fine for dozens of reasons to keep the tank at a quarter or more 'the majority of the time' for the peace of mine of the people in the car. It will in-fact strand all those people with a hard-fail fuel pump for absolutely certain if the car is not occasionally run down to low fuel light or even lower to single digits distance to empty.

It is the ONLY way to ensure that the main fuel pump has not soft-failed and that also the jet pump system is working as well (a few components could fail such as the pressure relief valve); the venturi pump has no moving parts, it's insanely rare that it could be plugged; gasoline is a good solvent and most things that could plug it will end up in the filter not in the venturi pump.

I would put 'goofed o-ring' as what happened to me in the 5% category at best, it looked like the car had original hose clamps, so factory defect is likely. The main fuel pump probably just had enough extra pressure to compensate until it started to fail.

This is an indisputable fact:

If you always refill your tank at a quarter, you will not know when your electric pump is starting to fail; you will absolutely get to a point where you can NOT use the last 6-8 gallons of gas with not knowing this fact. This is called false security, I am warning 'the world' since you seem to be deciding to ignore my wisdom.

When your pump fails it will not be a 'soft fail' that will let you get home with a can of gas, it will be a hard fail, because you will nurse a worn out pump without knowing until it simply can't turn anymore. There can only be these two options for a fuel pump; it will slowly give out less and less power at end-of-life or it will just up and quit.

With the billions of fuel pumps out there and the evidence supported in commentary online at the least, it is not hard to see that the majority of fuel pump failures are soft-fail; and that makes by far the most sense; as the commutator wears and the brushes wear, eventually they will lose their contact pressure and there will be voltage loss across the contact, meaning less power to the motor, it's quite simple physics and it will happen to every fuel pump ever unless something just up-and-breaks which is not likely to happen.

Down to empty = fuel light on. At the point the low fuel light comes on on MY x5, there is approximately 3 to 4 gallons of gas remaining. That means i can still drive 40-50 miles before the fuel pump risks being exposed to risk.

I don't recommend other people follow my practice of always running the tank down to the low fuel light. I am a 'hardened midwesterner' and if I myself get stuck on the side of the road at midnight that is just an adventure to me. I do however, trust the gauges and they have never let me down; when the low fuel light comes on, and even when i know it's coming, i've already mapped out exactly where my pit-stop will be to refuel.

It is not a bad practice at all to 'keep a quarter tank', it's only a bad practice to ALWAYS keep a quarter tank, as it will mask a soft failed fuel pump and you will eventually be VERY stranded, not just 'add a can of gas' stranded.

You say 'you will never have to rely on the siphon pump'; the siphon pump is required from half a tank and lower, it's just that when the main pump is weak, the depth of the fuel on the left side helps boost a weak pump and masks the failure. Failure is inevitable, the fuel pump is a consumable part with 4000 to 6000 hours life expectancy.

Refueling early will not prevent being stranded, rather the opposite, since it greatly increases the odds that a 'soft fail' will be masked and by the time you realize there is a problem, the pump will instantly 'hard fail'; easier to diagnose, but more likely to be a much bigger headache.

"shorten the life of" is synonymous with "damages"

'ran the fuel down to what'? is the question; down to 'low fuel' alert; nope that won't cause damage; 'down to an eighth of a tank', no extra wear; down to the dash gauge reading 0.0; for the x5, won't cause damage (aka reduce the lifespan). it's simply an untrue statement that can't be backed with facts, that's what caused me to react so strongly.

Your 'best reason' summary is exactly backwards, and that's my message (to everybody else since you aren't listening or seemingly understanding).

You are setting yourself up to be surprised when your fuel pump fails catastrophically with no warning. It's not an improvement to find out your fuel pump has died when it can't be nursed/babied to work 'sorta' where you can replace it on your time schedule and at your convenience.

If you do not occasionally run your fuel system by driving your fuel gauge down to zero occasionally, you do will not detect a soft-failing fuel pump, a condition that can last for 10s of 1000s of miles, and masking that condition will set up for the first symptom being that of a hard failure (completely stops working without notice).

Does it really matter if you can get to 160,000 miles vs 140,000 miles by filling up 200 extra times over that lifespan, if the end-result is being surprised by complete failure rather than a soft-fail being 'annoyed' that the car stalls with a quarter of a tank, a situation remedied short-term by a couple gallons of gas, compared with a tow to a dealer and $600-1000 invoice?

Pick the scary expensive path at your own peril; these are the facts.

The key is 'always'. if you ALWAYS refill without the fuel system going down to low fuel light, you will absolutely end up with a dead car requiring a tow in the end. If you on the other hand take my advice and at least once or twice a year, run the tank down at least to the low fuel light but better right down to single digits of distance to empty, you will be doing preventative maintenance to test the fuel delivery system to KNOW that it is working so in case you need it, it's there independent of if you NORMALLY never let the fuel get below a quarter of a tank.

I've never argued against the good reasons for keeping a tank not close to empty, i'm just explaining that *always* doing it is a very bad idea for the reasons stated up until now that have stranded me because it, hence 'my mission' to inform people unless they want to be stranded, test their fuel system once in a while.

My argument is; don't state things as fact that you can't back up, such as "running your tank low consistently" (not until it stalls just 0 miles to go) will reduce the longevity of your fuel pump. This concept does not apply in any way shape or form to the x5's fuel system. I'm not saying that other cars it could apply to, this is exclusively to the x5 (my contention). I've done many dozens of hours of research on specifically the x5's fuel system, and i know the facts, i've represented the facts, because there is too much misinformation out there about exactly how the system works.

Show me any specific item i've posted that i said that is incorrect so i can make sure it's accurate, but it has to be backed with fact/statistic/study not conjecture. I have the most detailed resource online for exactly how the x5 fuel system works. I know how long the fuel pump should last, i have a 'wear curve' showing how much weaker it gets over time, and based on all these things, i have a better grasp than likely 99% of drivers what to expect and why to do what, including specifically for the x5;

If you never let your fuel gauge get below a quarter, you will absolutely eventually end up with a tow to an expensive repair. There are only two options for fuel pump failure; fast hard fail (maybe 5% of the time) or slow 'soft failure' (maybe 90% of the time, as they are designed to do, they wear out, lose power), and 5% some other random thing causing a problem; pressure relief valve failure, hose breaks, etc.

One more time, just like my wife, it's perfectly fine 'for peace of mind' to refill at any point and refill to any amount (say fill at one quarter to only three quarters), but that is purely for the peace of mind of the driver and will have no bearing on longevity of the parts.

Should you make the logical choice to regularly refill at a quarter of a tank, than it's very important that you occasionally drive the tank down to empty to make sure the fuel pump has not soft failed yet or you'll be caught by a much bigger surprise than just needing a couple gallons of gas.

This is factual information for 'the internet' who happen to use bmw x5 and wish to avoid the shock of having their fuel pump hard fail with no warning. The easy to diagnose soft-fail is a much easier thing to take, manage and control, and should be the way anybody with an x5 or any bmw with jet-siphon pump system.

The sedan's use a different method to contain the 'surge tank' concept, and the values are different and I can't speak with authority on them other than exactly as x5; you NEED to test the 'down to empty' capability with any car that has a siphon jet system to make sure it's working as it's the ONLY way to test it; you can't test by pressure, volume weight, there are too many variables; it will work down to 0 miles DTE or it won't and only one way to test it; drive it down to zero. (once or twice a year; i recommend when the weather is nice 'just in case').

-awr

Your 'best reason' is false sense of security and is the main reason i've been posting the replies.

I was stuck on the side of the road for the same exact reason eventually YOU will be with HALF or a FULL tank of gas.

You will wear through the 'soft fail' zone of your fuel pump, since it will be masked by premature refueling and it will die completely, just as a recent post to xoutpost where the guy got towed to a gas station and refilled to the top and it wouldn't start because the pump was completely dead.

It doesn't matter if you were correct the whole time and premature refueling added lifespan, it is inevitable it will fail; fuel pumps last 4000-6000 hours on average.

If you follow the practice of refuel before the siphon jet does its job and empties the left side of the tank, you will never know the main pump has 'soft failed'. It will 'hard fail' and you won't get home with a can of gas, you'll need a tow and the main pump will need to be replaced before the car will operate.

My reasoning will get you home with a can of gas,

Your reasoning requires a tow and an emergency replacement of the main fuel pump.

I'm not sure why it's so hard to understand this concept.

To answer your questions,

Yes I did perform a test and mentioned several times.

At the particular depth of fuel on the left side of the tank, When the main pump was 'soft failed' and the o-ring was leaking, The right side test 6 only held 0.9L of gas, meaning the surge tank was no longer being kept full. When i replaced the main pump, that number went up to 1.1L of gas, clearly a difference but it wasn't being kept full to overflowing; i could take a hard left turn and slosh some gas into the surge tank, but after a minute or three, the level would even out at 1.1L again. What you missed was the 'leaking like a sieve' non-o-ring was from the connection that is not designed to be taken apart, and likely not part of the original equation of me getting stranded, i never got a reading of how bad it was when that was leaking, it would have been worse than when i started, it surely leaked more than the o-ring leak.

I may have 'put words in your mouth' about exactly how you said to keep a quarter of a tank. You said in separate statements that; ➀ you always keep a quarter tank of gas and that ➁ consumer reports said if you let your gas get too low it will wear the fuel pump. The 'take away' from those statements is that you decided based on things such as consumer reports that 'the appropriate amount of not too low' is a quarter tank. Based on your actions that is established fact. There may be other reasons also but the argument here is: is there any logical reason to put gas into an x-five from the engine's well being before the low-fuel light comes on. the answer is no, plain and simple. For the well-being of the occupants, you can come up with many reasons, i'm not arguing that point at all.

I don't want other people to get stuck on the side of the road as happened to me because of other people following the rule my wife did of prematurely refilling their tank always.

It is perfectly fine for dozens of reasons to keep the tank at a quarter or more 'the majority of the time' for the peace of mine of the people in the car. It will in-fact strand all those people with a hard-fail fuel pump for absolutely certain if the car is not occasionally run down to low fuel light or even lower to single digits distance to empty.

It is the ONLY way to ensure that the main fuel pump has not soft-failed and that also the jet pump system is working as well (a few components could fail such as the pressure relief valve); the venturi pump has no moving parts, it's insanely rare that it could be plugged; gasoline is a good solvent and most things that could plug it will end up in the filter not in the venturi pump.

I would put 'goofed o-ring' as what happened to me in the 5% category at best, it looked like the car had original hose clamps, so factory defect is likely. The main fuel pump probably just had enough extra pressure to compensate until it started to fail.

This is an indisputable fact:

If you always refill your tank at a quarter, you will not know when your electric pump is starting to fail; you will absolutely get to a point where you can NOT use the last 6-8 gallons of gas with not knowing this fact. This is called false security, I am warning 'the world' since you seem to be deciding to ignore my wisdom.

When your pump fails it will not be a 'soft fail' that will let you get home with a can of gas, it will be a hard fail, because you will nurse a worn out pump without knowing until it simply can't turn anymore. There can only be these two options for a fuel pump; it will slowly give out less and less power at end-of-life or it will just up and quit.

With the billions of fuel pumps out there and the evidence supported in commentary online at the least, it is not hard to see that the majority of fuel pump failures are soft-fail; and that makes by far the most sense; as the commutator wears and the brushes wear, eventually they will lose their contact pressure and there will be voltage loss across the contact, meaning less power to the motor, it's quite simple physics and it will happen to every fuel pump ever unless something just up-and-breaks which is not likely to happen.

Down to empty = fuel light on. At the point the low fuel light comes on on MY x5, there is approximately 3 to 4 gallons of gas remaining. That means i can still drive 40-50 miles before the fuel pump risks being exposed to risk.

I don't recommend other people follow my practice of always running the tank down to the low fuel light. I am a 'hardened midwesterner' and if I myself get stuck on the side of the road at midnight that is just an adventure to me. I do however, trust the gauges and they have never let me down; when the low fuel light comes on, and even when i know it's coming, i've already mapped out exactly where my pit-stop will be to refuel.

It is not a bad practice at all to 'keep a quarter tank', it's only a bad practice to ALWAYS keep a quarter tank, as it will mask a soft failed fuel pump and you will eventually be VERY stranded, not just 'add a can of gas' stranded.

You say 'you will never have to rely on the siphon pump'; the siphon pump is required from half a tank and lower, it's just that when the main pump is weak, the depth of the fuel on the left side helps boost a weak pump and masks the failure. Failure is inevitable, the fuel pump is a consumable part with 4000 to 6000 hours life expectancy.

Refueling early will not prevent being stranded, rather the opposite, since it greatly increases the odds that a 'soft fail' will be masked and by the time you realize there is a problem, the pump will instantly 'hard fail'; easier to diagnose, but more likely to be a much bigger headache.

"shorten the life of" is synonymous with "damages"

'ran the fuel down to what'? is the question; down to 'low fuel' alert; nope that won't cause damage; 'down to an eighth of a tank', no extra wear; down to the dash gauge reading 0.0; for the x5, won't cause damage (aka reduce the lifespan). it's simply an untrue statement that can't be backed with facts, that's what caused me to react so strongly.

Your 'best reason' summary is exactly backwards, and that's my message (to everybody else since you aren't listening or seemingly understanding).

You are setting yourself up to be surprised when your fuel pump fails catastrophically with no warning. It's not an improvement to find out your fuel pump has died when it can't be nursed/babied to work 'sorta' where you can replace it on your time schedule and at your convenience.

If you do not occasionally run your fuel system by driving your fuel gauge down to zero occasionally, you do will not detect a soft-failing fuel pump, a condition that can last for 10s of 1000s of miles, and masking that condition will set up for the first symptom being that of a hard failure (completely stops working without notice).

Does it really matter if you can get to 160,000 miles vs 140,000 miles by filling up 200 extra times over that lifespan, if the end-result is being surprised by complete failure rather than a soft-fail being 'annoyed' that the car stalls with a quarter of a tank, a situation remedied short-term by a couple gallons of gas, compared with a tow to a dealer and $600-1000 invoice?

Pick the scary expensive path at your own peril; these are the facts.

The key is 'always'. if you ALWAYS refill without the fuel system going down to low fuel light, you will absolutely end up with a dead car requiring a tow in the end. If you on the other hand take my advice and at least once or twice a year, run the tank down at least to the low fuel light but better right down to single digits of distance to empty, you will be doing preventative maintenance to test the fuel delivery system to KNOW that it is working so in case you need it, it's there independent of if you NORMALLY never let the fuel get below a quarter of a tank.

I've never argued against the good reasons for keeping a tank not close to empty, i'm just explaining that *always* doing it is a very bad idea for the reasons stated up until now that have stranded me because it, hence 'my mission' to inform people unless they want to be stranded, test their fuel system once in a while.

My argument is; don't state things as fact that you can't back up, such as "running your tank low consistently" (not until it stalls just 0 miles to go) will reduce the longevity of your fuel pump. This concept does not apply in any way shape or form to the x5's fuel system. I'm not saying that other cars it could apply to, this is exclusively to the x5 (my contention). I've done many dozens of hours of research on specifically the x5's fuel system, and i know the facts, i've represented the facts, because there is too much misinformation out there about exactly how the system works.

Show me any specific item i've posted that i said that is incorrect so i can make sure it's accurate, but it has to be backed with fact/statistic/study not conjecture. I have the most detailed resource online for exactly how the x5 fuel system works. I know how long the fuel pump should last, i have a 'wear curve' showing how much weaker it gets over time, and based on all these things, i have a better grasp than likely 99% of drivers what to expect and why to do what, including specifically for the x5;

If you never let your fuel gauge get below a quarter, you will absolutely eventually end up with a tow to an expensive repair. There are only two options for fuel pump failure; fast hard fail (maybe 5% of the time) or slow 'soft failure' (maybe 90% of the time, as they are designed to do, they wear out, lose power), and 5% some other random thing causing a problem; pressure relief valve failure, hose breaks, etc.

One more time, just like my wife, it's perfectly fine 'for peace of mind' to refill at any point and refill to any amount (say fill at one quarter to only three quarters), but that is purely for the peace of mind of the driver and will have no bearing on longevity of the parts.

Should you make the logical choice to regularly refill at a quarter of a tank, than it's very important that you occasionally drive the tank down to empty to make sure the fuel pump has not soft failed yet or you'll be caught by a much bigger surprise than just needing a couple gallons of gas.

This is factual information for 'the internet' who happen to use bmw x5 and wish to avoid the shock of having their fuel pump hard fail with no warning. The easy to diagnose soft-fail is a much easier thing to take, manage and control, and should be the way anybody with an x5 or any bmw with jet-siphon pump system.

The sedan's use a different method to contain the 'surge tank' concept, and the values are different and I can't speak with authority on them other than exactly as x5; you NEED to test the 'down to empty' capability with any car that has a siphon jet system to make sure it's working as it's the ONLY way to test it; you can't test by pressure, volume weight, there are too many variables; it will work down to 0 miles DTE or it won't and only one way to test it; drive it down to zero. (once or twice a year; i recommend when the weather is nice 'just in case').

-awr

In all my years of driving the X5 I have never been stranded by the side of the road, you, however, have been stranded twice. My X is currently at 158,000 miles with the original fuel pump.

Besides, if I do get stranded there's always AAA. :bustingup

Perhaps once the weather is warm enough to work on the X, I will replace the original fuel pump with another fuel pump. Before replacing the fuel pump I will probably run it down so there will be less gas in the tank to contend with. Like Best4x4xFAR the OP I will probably not buy an OE fuel pump since I don't plan on keeping the X for another 16 years. :bustingup

Surprise that you didn't come upon this article in your many Hours of researching electrical fuel pump failure.

https://www.yourmechanic.com/article...-cheryl-knight

or this one

http://www.consumerreports.org/cro/n...stly/index.htm