Fuel pump recommendations

[andrewwynn]

E39 not like e53. Completly different system.

There is absolutely no difference in how deep the fuel pump is submerged once the tank has > 5L. The design is completely different from road cars. It's designed to keep the pump submerged when going up and down hills and keep the pump submerged when low on fuel.

"Below 1/8 risky" is absolutely incorrect when referring to the E53. In road cars that may still apply. Last time I checked this is the E53 forum where that rule does not apply even a little.

In addition, should you follow that rule (1/4 or 1/8 rule) you INCREASE your chances of being stranded. I know this from first hand experience!

My wife used to use the 1/4 tank rule. It masked the fact her fuel pump was worn out and left me stranded. The ONLY ways to test the function of the siphon jet is to either drive down to single digits DTE occasionally or add a fuel pressure gauge to the return line from the fuel filter and confirm you have enough pressure.

A siphon jet not working will cause a fuel starvation problem with fuel in the tank but it will not damage the pump UNLESS you ignore the problem and try to nurse the situation by keeping the tank full enough (again a case where keep 1/4 tank will cause a problem)

I've seen hundreds of posts about siphon jet and fuel pump failure. I've spent about 20 hours researching how the E53 fuel system works.

I found not one single page that describes the fuel system accurately for the E53 so I literally "wrote the book" with the singularly unique but accurate depiction of how rhe fuel system works on the E53. Literally the only accurate description online that I've seen.

The sedan fuel tanks are different: the lobes are similar left and right. There's a baffle to keep fuel near the pump on hard g-forces but completely different from the x5 which has an actual sub-tank that holds about 5L of gas and will hold exactly that from 30L of gas until 5L unless the main pump or siphon pump have failed. What that literally means is that the x5 does not know the difference between 5 and 30L of fuel.

There are no moving parts in the siphon pump, the only failure points are either a seal or the over pressure relief valve.

After reading hundreds of posts about such failures I determined that the electric pump failing is nearly universally the cause.

90% electric
5% siphon
5% something else (Filter/FPR)

Even when there is a problem with the siphon (leaky seal) once the weak electric pump is replaced, the siphon will work again.

That said, when I ever replace an electric pump I will check for leaks on the siphon side because it's a crappy design with one joint having no actual o-ring seal.

To repeat: zero advantage of keeping more than 1/8 tank of fuel in the E53 only adds inconvenience and more likely to mask a failing fuel pump and increase the chance of being stranded.

If you "always" fill at 1/4 (1/8) tank you will absolutely get stranded because of the practice eventually because you will mask the failing pump and the DTE at engine stall will slowly get higher until it rises above the percentage you arbitrarily decide to fill.

If you on the other hand as I do, drive to the low fuel light you test the siphon jet every tank and will know right away when your pump dies.

My wife's pump was broken for about 9 months before I found out at 6°F on the freeway because she used the 1/4 tank rule. Had she not followed that bad advice I would have known in April not December and could have changed the pump when it was 60°F vs 0°F

e53 Fuel Supply Detailed (fuel pump / siphon pump diagnostic help)

https://r.tapatalk.com/shareLink?sha...6&share_type=t

[Crowz]

Low fuel levels on ANY vehicle with a submerged electric fuel pump is baaaad.

The E53 may not suffer the transfer issues the others have but the keeping the pump cool rule still applies.

On my vehicles that never run low on fuel (translation : I don't let my wife drive them) the pumps have never failed. My 323i for instance has the original fuel pump in it with over 400,000 miles.

I treat 1/4 tank as empty. Of course your always going to have those once in a blue moon lower deals trying to find a station. But as a general rule I never let the vehicle get below 1/4 tank.

My wife on the other hand thinks the gas gauge is a devining rod that lets you know there is gas around there somewhere and under 1/8th means you should get around to getting gas sometime, maybe, kinda, soon.

She goes thru fuel pumps.

[andrewwynn]

Crowz: you have a conceptual error in how the fuel tank works in the E53: the fuel pump will be entirely submerged until you have zero L left on the gauge. There is about 3-4L fuel that is not reported by the gauge that will keep the pump submerged down to 0.0L on the fuel gauge.

I would have to do similar research on how the other car models work but the E53 fuel tank is different from all others and there is zero benefit from the inconvenience of chopping 100 miles from your range and greatly increasing the odds of stranding yourself the first time you go a little deep into the gauge.

If you always fill up at 1/4, there is nearly a year100% chance the fuel pump will fail without you knowing it as the vast majority of pumps will just get weak vs fail completely fail. That means you can be like my wife, drive for a year with a broken pump that leaves you stranded the first time you try to get to 1/8 of a tank.

400,000 miles would be the AVERAGE life driving 62mph so if always highway miles that is not that abnormal.

Heat is not the primary concern. Especially with the x5 since if you do run it dry the farthest you can drive once the pump starts to be uncovered is about 10 miles. The brushes simply wear out. When they are worn enough the spring pressure drops the resistance rises and the power to the motor drops and it gets weaker.

The wife used to use the 1/4 tank rule her pump made it to about 128,000 I drive until the low fuel light comes on my pump is going strong at 157,000 (miles).


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[Overboost]

Originally Posted by andrewwynn

I drive until the low fuel light

Guilty as charged back in the rough days of 2009...

[andrewwynn]

I did the math once. It has saved me well into the 100s of hours not seeking gas stations and filling up in the nearly million miles of my driving history.

I've had one fuel pump die on me while driving (stranded) and it only happened BECAUSE of the erroneous concept that 1/4 tank rule helps (absolutely does not: prove me wrong you can't)*

* I only drive x5 wife has one I have one so only applying to x5. Supposition and myth does not apply proof requires absolute fact.


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[Crowz]

So where is the part of the e53 tank that makes it unique?

I haven't found anything diagram wise besides the one above.

[Crowz]

As in what does it have that makes it special for offroading angles and such?

[Crowz]

Crap I just went through my files and I cant find the test we did for this. Its been years but I should have it somewhere.

But I have everything to do the test again except a tank and I can even film it this time around. Youtube didn't exist back when we did the test before.

I have my sons old pump from his Chrysler sebring so I can use it to run the test with. I will post the info when it warms up a bit and I can do it. We proved back in the day the effects of pump cooling by testing the following.

1. Submerged or not.

2. Submerged in small trough or canister vs outside fuel present or not.

3. Gallons of gas volume increased in test tank 1 gallon at time (that one took daays of tinkering to get the fuel back to the ambient temp each time)

Temps were measure for gas itself, the pump itself, gas in canister surrounding the pump, and also direct measurements of the canister housing and sending unit (pump holder).

Was fun testing last time so should be fun to do again.

I'll post up the results when I get them done. Was surprising last time so Im hoping it works out that way this time too.

The only difference this time around is I will have to come up with a tank to do the test with. We cut the top out of a trucks plastic gas tank for the test last time.

[Crowz]

Oh and note to self - THIS time around I will NOT use the wifes kitchen probe thermometer.

That part was ugly.

[andrewwynn]

The diagram above is NOT from e53. Read my thread it details all aspects of e53 tank and why it is different from all other fuel tanks.

ALL of the fuel goes into effectively a 5L gas tank. The car is unaware that the tank holds more than 5L of fuel because once there is more it spills out over to the left side. This starts at approximately 27left 1.5L right. Once below about 28L total the right size will report 1.4L or so (the last 3.6L is unreported).

The fuel does go in circles which will cool the liquid more than if it was just the 5L but there is never more than 5L surrounding the pump once the total fuel is about 28L of gas. (30%).

Yes, really. The bottom of the right side of the tank is approximately MIDDLE of the depth of the left side. The surge tank is in the back of the right side and it's a "dent" who's top lines up with the bottom of the right lobe of the tank.

See my diagrams and photos. Like I said, after 25-30 hours of research I found ZERO accurate pages describing the workings of the E53 Fuel pump. They all used inaccurate references based on the sedan designs and were wrong, every single one.

When I eventually figured out exactly how it works (even siphoning out the surge tank to determine it's exact volume) I literally know more about the E53 pump than any accessible resource online so I shared that info with xoutpost because they are deemed by me to be the most worthy of my contribution.