Cooling system runs at 2 bar, thoughts on 1.4 bar?
 

So yea, ever since I developed that retarded leak in the valley pan area. I have been making up a huge part list and doing a shit load of research. Our BMW cooling system runs at 2 bar. Yes, that is nearly 30 psi of pressure. The new BMW cars, seem to be running at 1.2 to 1.4 bar.

Here is why I am questioning this 2 bar pressure cap on our cars.

I did a cooling overhaul as my expansion tank cracked. I couldn't get to all the hoses, and clearly some gaskets. I replaced the damn cap too. I need to find if I still have my old cap, because I am sort of suspecting that it was not 2 bar.

So, I now have a leak.

Now I have been doing a lot of reading, and it seems quite a few people are switching to the 335i cap, which is 1.4 bar, and the system runs fine.

The industry standard for coolant pressure is 1bar. Thew new BMW are 1.2 bar. I think the 2 bar caps are overdose for our systems, and are actually to blame for the catastrophic coolant hose and component failures.

Does anyone have any experience with putting on a lower pressure relief cap on the e53? This just makes way more sense.

how much is the 335i cap?

German Auto Solutions sells a 1.2 bar cap in anodized black and red, as apparently they think the system pressure is too high as well. Its 35 bucks, but I'm definitely going to put a lower pressure cap on my X.

If the 335i cap is cheaper, and fits our expansion tanks, let me know and I'll get one of those man!

EDIT: I don't think the 335i cap fits the M54, but it might cross reference on the 8 cylinder expansion tanks!

Here is the link for the GAS cap:

Buy G.A.S. BMW 1.2 Bar Coolant Cap

The E93 335i cap is $12.00
Home Page Search SiteSearch 17117521071 ES#38106 Coolant Expansion Tank Cap - 17117521071

There must be some factory 1.4 cap that fits the M54. The GAS cap is not that expensive though.

The more I read on this, the more I question this 2 Bar pressure that we are running, with plastic parts. The only reason I see us needing 2 bar vent, is when you shut the car off, the pressure in the system can spike. Pressure will build, and we have a chance to vent, thus spill coolant out with the lower pressure cap.

But, this will spill the coolant out through the cap, and not blow a damn hose out. I think this is exactly why my car has a leak all of a sudden. I replaced a lot of hoses, tank, cap. I couldn't get to two hoses, which I will get to now. So, without really confirming this with a pressure tester, I have a feeling I moved the next weakest link down the coolant system chain, and now either blew the rear manifold hose, or the valley pan gasket.

I agree with all you're saying, basically unless you replace all the parts you are putting stronger parts in the system (new) and leaving older, weaker parts in, and with 30 psi, you're bound to force a leak somewhere.

I'll be picking up a GAS cap to keep my pressure at manageable levels and to pre-emptively hopefully extend the life of my cooling system components. GAS doesn't mess around, their DISA rebuild kits are bulletproof so I don't gather I will have any ill effects from this.

There are a shit load of people on bimmerforums that are running the GAS 1.2 bar caps. The e39 guys too.

I have a feeling the V8 cap, and your cap are the same. GAS doesn't list the 4.8is on the fitment, but it does list the the E65/E66 740 and 750. A quick part search on RealOEM shows us that your cap, and mine are the same.

RealOEM.com * Part Cross-reference

So the 335i 1.4 bar cap should fit your car as well.

awesome, yeah I saw that.

Its definitely a bigger cap than stock though, that might bother me. Either way I think you and I definitely need to start a revolution switching to 1.2 bar caps.

GOSH DARN I AM 2 FOR 2 TODAY, I'LL TAKE ANOTHER CIGAR PLEASE!

Want an OEM looking 1.4 bar coolant cap that will fit the E53 tanks?

E30 cap FTMFW, you're welcome! and it's 15 bucks from BMW

Home Page Search SiteSearch 17111742232 ES#37938 Expansion Tank Cap - 17111742232

I am going to go with the factory e93 1.4 bar cap just to test. First I need to figure out my damn leak, fix it, monitor the KTMP in the OBC with the factory cap, and then switch to the 1.4 cap while also monitoring the KTMP. I don't want to deal with any weird temp issues.

It doesn't make sense why we are running 2 bar, when Ferrari is .9 to 1.1

Industry standard is 1 to 1.4 bar.

No shit BMW recommends you overhaul the entire cooling system when you get a leak.

Even better. Looks like mine. Thanks.

Look what I found. 1.2 bar E30 cap. Whaaaaat

Home Page Search SiteSearch 17114379047 ES#38066 Expansion Tank Cap - 17114379047

Actually the cooling system DOES NOT run at 2 bars. The venting valve of the expansion tank is set to open at 2 bars, which is overkill, and effectively will allow for plastic components to rupture abruptly, loosing lots of coolant in the process. The 1.4 bar venting valve is OK. I use a 1.2 venting valve on the e39, and I haven't had any issues. That car was also designed with the 2 bar venting cap. During the last year I added less than 1 oz of coolant.
Lowering the venting pressure, will allow to loose some coolant through the cap - but you have to be careful. the plastic components probably won't break, but you have to monitor, so you don't loose too much coolant and overheat (in case something goes wrong).
Also, lowering the venting pressure, you have to make sure your coolant level is not higher - it will build up more pressure and you will start venting if the temps go high. If the coolant level is lower, it allows for more expansion of the coolant, but this is also not desired.

It looks so 80's, lol. I'm gonna order the 1.4 bar E30 cap I posted, I have a few parts to gather from the local dealer (oil filter cap, windshield upper molding, strut dust cap) so I'll report in a few days when she is in and installed.

So Doru, effectively replacing with the 1.2/1.4 venting cap will allow for more coolant loss (as that pressure might be reached more frequently) but should avoid ruptures to an extent because the venting pressure is brought down?

Basically the cooling system is going to vent whether you like it or not, and would you rather have 30 psi or 18/20 when that happens?

Yup, I am going with the 1.4 as well, the one you found. I have a huge list of parts that I'm ordering. Going through Craig at Open Road BMW. You can't fine a better price. 15% over cost. Let me know if you want me to post up his info.

To reach 1.2 bar DIFFERENTIAL pressure, the coolant should be above 126°C - that's in an M54B30 engine. That's pretty high.
You should NOT loose any coolant with a 1.2bar or 1.4 bar cap. If you loose coolant, it means your coolant went above 126°C (1.2 bar cap), which in turn is a different problem (stuck t-stat comes to mind)
The 1.2 bar cap I purchased from GAS. here is a short reading about the pros of 1.2 bar cap

And here is a debate about the subject (1.2/1.4 bar vs 2 bar cap). This will shed some light whether to go this route or not.

I read that entire thread and a few others over the past few days. ahahah, funny you found that.

If you haven't already done so, use the BMW ETK (on realoem.com) for your car and VIN number to be sure what your X5 should have. One alternative to suggest, the factory pressure cap on my 2002 X5 3.0 diesel, it's rated at 1.4 bar. Part number is 17 11 1 742 232.

Note that later BMW E30 (facelift from memory) had a specific low pressure cap as part of a US market recall to minimize blown heater cores and the resulting scalding / burning a driver's right shin from the gush of hot coolant. Research this a bit, but from memory it was rated under 1 bar.

Aha! Awesome find guys! The theory sounds plausible and will be getting a lower pressure cap as well.

Been thinking of the cooling system because though I have replaced all my cooling system hoses, I just realized I have a nest of heater hoses I havent replaced yet.

Doru, thanks for translating the vent pressure to a coolant temp needed to vent.

I havd a habit of monitoring my OBC coolant temp and driving I get up to around 92 and spike to 96 at the most briefly. Engine off I've never seen it reach 100.

What temps are you guys seeing in your OBC's?

If you look at post 7, that is the same part number as the one you provided. You sure that is a 1 bar cap.

I would recommend leaving the system as is. And don't overfill.

.02

:iagree:

If we go back to basics, the cap release pressure isn't what the system is running at, but rather when it vents. The highest temperature is probably during a heat soak after a hot shutdown. If the system can't handle 2.0 bar without rupturing, I suggest it should be fixed. Putting a 1.4 bar cap on there is a band-aid solution to a separate problem, either that the vehicle is overheating or that one or more components are aged and weak. All you are doing by using a 1.4 bar cap to avoid the problem is delaying it happening. How many leaks are there that won't happen at 1.4 bar but will at 2.0 bar?

And why risk the chance of having to top up the coolant more frequently due to occasional venting from using a lower rated cap? If all vehicles were having this problem in the first year after product release then there would be reason to consider if there was a design problem. But if it is first happening when the same vehicles are ten years old, then it is a maintenance issue. Just fix it right. My $0.02.

Agreed JCL and like I was telling slick, I don't just recommend slapping a lower bar rad cap on a ten year old cooling system and doing nothing else.

I'm more along the lines of when a cooling overhaul is done, and relevant parts, hoses, Tstat and water pump etc is replaced, and the coolant is flushed and refilled, then if you so chose at that point to replace with a lower bar cap then you can do so with most likely no different operation or ill effects.

I agree with you that the system must first be fully operational, coolant levels correct, etc, before worrying about what cap to go with

It just seems misguided to me. If I had a tire that had a slow leak at 30 psi, I wouldn't consider it to be a reasonable solution to run it at 20 psi. Even if it did hold that pressure without dropping further.

LOL. No. I don't plan on just replacing the cap with a 1.4. I fully plan on fixing it with the regular cap. I am just curious to see why we have a 2 bar one.

So you're sticking with the 2 bar stock cap Slick? I don't think the 1.4 bar cap would give any ill effects, as like Doru said, unless you have some issues where you are overpressurizing the system often enough to be losing coolant, then you probably have other cooling issues. However, with the 2 bar cap I am almost certain you'd be venting less because of the higher pressure, whereas you are more likely to reach the 1.2/1.4 bar pressures in normal operation on hot days etc, and it might be venting more often, which might require additional coolant on more frequent occasions than the stock cap. Personally I have not had to add coolant since I bought the X in 2 years, and I'm ok with that.

I will admit it is funny about the misconception of how the tank cap works, especially in the discussions on BF and the like, most think that it actually lowers the normal running pressure of the cooling system which it does not do at all.


Regardless, I'll be sticking with the stock cap until I have to do some cooling system replacement items and a flush (probably in a year), and normally i'm a "if it aint broke don't fix it" kinda guy, so I might end up with just the same 2 bar cap when I do replace it someday anyway.

No I will put on the 1.4 bar cap for sure. I will just find all the weak links in my system with the 2 bar. I think it is worth a try.

Sounds good man I'm hoping you find your leaks and glad i was able to find "our style" cap in 1.4 bar for you, when i do my cooling overhaul next year I'm sure that will be part of it.

Glad you found the leak! That test kit comes in handy eh?

Just throwing this out there..... if the 1.4 bar relief cap doesn't operate under normal conditions, it will not help the system stay sealed any more than the 2 bar cap. If it does operate under normal conditions, it is not rated high enough for the system. A certain relief cap will not raise the MTBF of hoses / seals / expansion tank / etc. It is unrelated.

reviving an old thread (sry)....

I'm about to change the Expansion tank and was curious to have some feedbacks on long-term testing of the lower BAR caps.....

Should I stick with the original 2bar or go with the 1.4bar?

Thx!

Gio the only difference the cap does is make the "safety relief" of venting pressure if it builds up to 1.4 bar instead of 2 bar, it makes no difference on normal operation of the system.

Assuming your coolant is 50/50, not overfilled, and your system is running at normal operating temps, the 1.4 bar cap will behave exactly as your 2.0 bar cap, except if there is a problem in your system and the pressure builds it will vent at 1.4 bar instead of 2.

Normal operating of the system never gets above 1.0 or 1.1 bar, assuming what I said above is correct. If you have more water in the system than coolant, higher pressures can build. If you have overfilled expansion tank, higher pressures can build.

Personally I'd rather have the "safety relief" at 1.4 bar than 2.0 bar, so I will be putting a 1.4 bar on in the coming weeks. My expansion tank, hoses and T-stat have been replaced about 3 years ago so my system is in good shape.

Thanks Ricky , I'll go that route also. As you've read on some other thread , I replaced the bleeding screw (leaking) but I probably overfilled the tank when I topped it so the next day , the expansion tank now is leaking form a pin hole... I hope I did not damage anything else.

Would you have the part number of the cap you'll be using by any chance?
This one?
Home Page Search SiteSearch 17111742232 ES#37938 Expansion Tank Cap - 17111742232

Then put a gallon of premix coolant in the luggage compartment for any occasions when the system vents at 1.4 bar but wouldn't have vented at 2.0 bar as designed. And keep it topped up.

Or just use the correct cap.

Good point also but thats exactly the debate of this this thread. And thats exactly what i want to know from longer time users. Does it vent abnormally and need to be topped up often because of it?????

Just. Use. The. Correct. Cap.

I. Will. Sleep. On. Your.Words. Of. Wisdom. ;)

I'll be on the hunt for parts tomorrow morning (expansion tank) and will make sure to include a NEW cap.

An analogy would be that if you were worried that driving at very high speeds could wear out your cooling system sooner, you could install tires that had a lower speed rating, but cost exactly the same. They would be identical to the proper tires, but could not handle higher speeds. That way, if you ever actually drove too fast, the tires would fail before you hurt your cooling system. Yeah, that would make sense.

I don't know how often a lower pressure cap may release. But why would you ever want to find out? The vehicle would have boiled over, and be low on coolant. All that trouble to try and save a soft rad hose or cracked expansion tank that was about to fail anyway?

I understand a cooling system. But there is nothing wrong in questioning german engineering once in a while. Recalls are exactly that; admitting something is wrong and replaced by something that will help resolve a repetitive fail.
Ok , granted , there is no recall for the cap but sometimes the majority is right and german engineering is wrong. Not saying this is what is happening in this case and I will probably end up with the 2bar cap this morning.

Expansion tank failure???? What a farce!!!

I am using a 1.4 e30 cap for about a month now. Not worried about high RPM or anything leaking out. Everything is fine. All my hoses are new. New T-stat, expansion tank, all the sensors in coolant. Only thing I haven't changed is the water pump or radiator. I don't plan on changing them till I get over 100k miles.

First of all, the system hitting 2 bar while driving is just retarded, and you have more important things to worry about than a cap venting.

Second, the pressure spikes when you drive hard, then shut the car off. Not one person with has "vented" with an e39 running a 1.2 bar cap and posted about it. There were some, but they overfilled. Once they vented the excess, it doesn't vent any more.

I still have the same amount of coolant in the tank as I did when I put the e30 cap on. I keep it a bit below half plunger. Since I put it on, I checked it about every weekend before I move my car outside to work in the garage. Huge pressure relief sound when I open it up every time. PSSSSSSSSSST. I also have a tiled floor in the garage, so any "vent leak" would be very easily spotted. I mean I found my old drip leak that way too. Porcelain tile doesn't seem to absorb coolant very well, lol. Since I park in the garage after parking, that is when the pressure spike should happen, the fact that it is all dry, means the system will work just fine with a 1.4 cap.

My logic is a bit different. I think BMW is playing a cruel joke on us with the 2 bar cap. I also have this nagging sensation that is is made 2 bar solely for one reason, make us buy more parts. Especially when half the crap in the cooling system is plastic.

Again, chances of you going over 1.1 bar while driving is slim. There is a guy on e39 that ran with a gauge in line, AC, heat, over 100F outside, 1.1 is highest he went. I would rather vent at 1.4 bars when I shut the car off, than cause unnecessary pressure on all the plastic shit in the cooling system.

So I think all is good in the hood.

JCL, lets presume the pressure goes to 1.5 bar, while you are driving. Your cap isn't exactly going to open up and dump all the coolant out. It will open up to reduce pressure, but close once below 1.4. Yea you might lose some coolant, not all. But if you were running 2 bar cap, your neglected hose/gasket that you forgot about, will blow up, and will dump everything you have.

Venting will most likely happen during a heat soak after shutting it off hot. It won't likely happen while the vehicle is operating, because you have airflow, coolant circulation, and so on.

It is unlikely to happen in this weather in any case.

You really open the cap to check the cooling system every weekend? I can't remember opening my hood on any car that often, since a 76 Ford 400 cid V8 that needed valve guides in the early 80s.

I am nervous. I am only doing this till my heart is content that everything is working fine. Few people on here, whose opinion carries weight, have suggested not doing this. YOU, made me nervous. lol.

Wow , I'm sorry I have revived this old thread now. lol

I ended up grabbing the original 2bar cap... New hoses , new expansion tank.
New hoses because when changing the expansion tank , the quick connects did not seal anymore , I was forced to order all new hoses. So basically with that logic , every time the expansion tank fails , the hoses need to be changed????? 200-300$ extra.
How possible is it that it's the cap (vent) that fails and makes it impossible to vent out the pressure? Maybe it's as simple as changing the cap every 2 years as a prevention work. 20$ :dunno: :dunno:

I use the 1.2 bar cap for almost a year now. "0" issues so far, even in hot temps during summer. I checked the coolant level oddly enough last weekend, and it was at the same level it was at the end of summer.

To JCL: if BMW would have placed a 4 bar cap, would you run that one too? Just curious.

If BMW had installed a 4 bar cap from the factory there would logically have to be some other reason for it, since the system wouldn't normally get to those pressures. But if it was factory supplied then I would expect that the cooling system was designed for those pressures and that all components subject to higher pressures were validated during the development phase. So yes, although it is an artificial example, I would leave it there.

I used to lead an engineering product development team for a tier 1 automotive supplier. Automotive components are usually spec'd for a reason. The important thing is to know the reason for a performance spec before attempting to redesign a portion of an integrated system. Always watch out for unintended consequences.

Radiator caps used to be ne of the regular things changed when a cooling system was being repaired, back in the day. They were considered a maintenance item. I used a radiator cap pressure tester as part of every cooling system check, to check the seal and the release pressure.

These days, a cap failure is more likely to be caused by improper coolant, deposits, hard water, and so on, IMO.

BINGO!!!!!!
So they (BMW) have the SAME 2 bar cap for all model range cars built between 1997-2003, but not so for different other years. One more thing to make this confusing is the fact that the 2 bar cap was used on 4 cylinder, 6 cylinder and 8 cylinder engines. Each with different temperature AND pressure related specs for their cooling system. Enter the bean counters, and the result is: use the 2 bar cap for every model lineup, no matter the engine displacement, cooling spec etc. It's much cheaper......
And I think even for the v8 the 2bar cap is overkill. Also loosing coolant slowly might allow you to salvage the engine vs. a sudden rupture of any of the cooling components with a total loss of coolant. The temp needle and the "gong" will be there in both cases.
just sayin'

I don't understand your point.

If a 2 bar cap was used then components like the expansion tank would have needed to be validated against that expected maximum pressure. The operating pressure will be different for each model, as you say, but what does that have to do with designing, building, and testing the expansion tanks to handle 2 bar plus a safety factor? It would be far cheaper to have one expansion tank spec than a different one for each model. The bean counter argument works in both directions.

The system was designed to have a 2 bar cap. It worked that way for 6 years of production, according to your data, and has worked for 10+ years since then. If a failure occurs now, it is not likely a design issue, or a manufacturing issue, but a (lack of) maintenance issue. Latent design issues don't hide for up to 17 years and then jump out to bite you. And putting a lower pressure cap on it is just a band aid designed to cover up poor maintenance practices and low quality aftermarket parts, IMO.

My parts are all new, and OE purchased from Open Road BMW. Even the e30 cap.

Then you should quit worrying.

Again and I'm glad Slick chimed in, as well as Dorin. I understand and agree with JCL that it was spec'ed for a reason, but I still will most likely switch to an E30 1.4 bar cap down the line. My M54 doesn't get run in the Arizona desert, and even after running in the summer and shutting down when hot, my pressures won't rise high enough to 2 bar, or even come close to 1.4 bar.

My hoses, expansion tank, t-stat, are all new and my coolant is filled to proper level with 50/50 mix. The first thing like I said earlier in the thread, be sure your cooling system is up to snuff first, coolant cap pressure should be last thing to worry about.

I'm not gonna argue in here with the others, but there are members running the 1.2 or 1.4 bar (in Slick's case) cap with not a single issue whatsoever, no losses of coolant anymore than before they switched the cap, so this tells us that the system pressures don't go anywhere near the 1.4 bar E30 cap, let alone ever get to 2 bar.

Point is, if the system is getting enough pressure to vent at 2 bar, you better be pulled over with the car off bc you have bigger problems.

Since I would never let my system get up to those kind of pressures, I have no issues using an OEM 1.4 bar coolant cap in the future, or a GAS 1.2 bar cap as well.

It's not about "using the correct cap", its about making sure your system is up to snuff, parts wise, mixture of coolant wise, etc. Like I said prob on the first 1 or 2 pages, REPLACING THE COOLING CAP IS NOT A SOLUTION TO ANY PROBLEM WHATSOEVER. But as Slick has shown, and many many E39/E46 members have shown on forums outside of Xoutpost, there are no negative effects to lowering the "safety valve" on our cooling systems to 1.4 bar with an OEM BMW part.

I respect the 1.4 bar "testers" and good for you if you have great results. I went with the original 2 bar cap (it was in stock , not the other or I would have put the 1.4) , but either way this cap looks cheap and I will inspect and replace more often from now on for cheap cheap insurance. I'm convinced it's the culprit of MOST coolant system problems. IMO

I actually have it for a different reason. I want it to vent, at 1.4 to show me that there is an issue. Waiting for a 2 bar cap to vent, good luck.

Like I said before, chances of you hitting 2 bar while driving is slim to none. But once you pull over, shut the car off, you might come back to a blown hose. I am not sure what the 2 bar cap is supposed to accomplish. The pressure increased temperature difference is negligible. I really do believe that it is meant to abuse the shit out of our hoses when the car gets shut off. Maybe it is BMW way of making sure the hoses fail when the car is shut down. It really is a retarded way to force a failure. I doubt it hits 2 bar, or even 1.4 bar often, but why would the cap be set so high?

If you want to say that BMW is a performance machine, Ferrari uses a system under 1 bar. No one else in the auto world uses a 2 bar system.

I'm telling you, BMW is making a killing on selling all these hoses, expansion tanks, and coolant for every used BMW out there. And it is a lot of cars with the 2 bar cap. A lot, like almost all of them.

Why I believe 1.4 is the way for me. When I turn off the car, and it hits 1.4, enough to vent it, I will know I have an issue somewhere.

If I have a 2 bar cap, and blow a hole in my expansion tank, I might be thinking the tank is old, and not even bother looking if there is some other issue.

If my hoses or tanks start to leak with the 1.4, then I know my components are due for a change. At least I will know I am not blowing them apart.

And we keep talking of hoses and expansion tanks. You guys are forgetting one part that every M62 suffers from. The valley pan. Unless you plan on including the VP gasket in every coolant flush, or system refresh, you are going to blow a hole in that one too.

I've read that if you lower the pressure of a system made to function at a higher PSI , you can create cavitation (surface bubbles) , this can cause the engine to run hotter.... :dunno:

Gio the rating of the expansion tank cap does not change normal operating pressures of the system. Normal operating pressure is around 1 bar.

This is a common misconception with the coolant cap, it only vents at that pressure it is rated for, but normal operating pressure of the system is the same regardless of the rating on the tank cap.

Exactly , if it was operating at 2 bar and we'd lower the pressure valve at 1.4 bar , then there would be a possible problem. But because it operates at closer to the 1bar mark then the 2 bar cap is totally irrelevant .

Makes sence....:thumbup:

Low coolant level gong means shut it down. Same thing you'd naturally do during catastrophic failure. Limping along isn't salvaging but rather risks low flow + localized hot spots. Also the OEM temp needle is a joke.

I know it's a joke. But I'm not driving daily with the KTMP on. There are cases when I do so though.
If you start loosing coolant with a 1.2 bar cap or a 1.4 bar cap, you can check where the problem is. With a 2 bar cap, usually it's catastrophic and you loose almost ALL of the coolant rather suddenly. This is my point.
G.A.S. tested thoroughly the pressure caps and here is their findings:

"So what is the solution? The system does not need to run that high of a pressure. In fact the industry standard for cooling system pressure is 1.0 to 1.4 bar. After doing extensive research and beta testing on several BMW engines, we decided on an optimum pressure of 1.2 bar. This pressure is high enough to maintain OEM pressure specifications up to 126 degrees Celsius (260F), which means that our cap will not alter your cooling system efficiency in any way. Apparently even BMW has seen the light, since most current BMW models now come equipped with a 1.2 bar cap.
Our cap will limit the maximum coolant pressure to 1.2 bar (17.5 psi) instead of the OEM spec of 2.0 bar (29 psi). Even something as simple as overfilling the coolant recovery tank a little higher than the recommended level will result in potentially damaging pressures when using the stock 2.0 bar cap.
We want to be very clear... cooling system components can fail due to cracking even at normal operating temperatures and pressures. Our cap will not guarantee you will never experience a cooling system component failure, but it will drastically reduce the chances of catastrophic ruptures.
The German Auto Solutions 1.2 bar Cooling System Cap uses 100% original BMW internal components that have been recalibrated to vent at 1.2 bar."

In layman words: If your system runs consistently at 126°C or over, the 1.2 bar cap will start venting. Meaning that your car has serious problems and IF you have the 1.2 bar cap, you can shut the car off and check what's wrong.
On the other hand if you have the 2 bar cap, it will NOT vent, the temp raise even higher. The cap will hold 2 bar, but maybe the other plastic & rubber components will NOT, hence a sudden rupture. Checking what's wrong, it's too late now. The damage is there, and the car is absolutely not driveable. This at best. If you are in a spot where you cannot safely pull over, you also run the risk of overheating, because with no coolant driving an additional couple hundred yards to a safe spot might do it.

Hope this clears it up. For me, the 1.2 bar cap (with OEM BMW safety valve) does the job rather nicely. If you are not comfortable with that, you can use the OEM 2 bar cap as designed (and curse BMW, if God forbids you run into a stuck closed T-stat, or whatever). There are people who don't change fluids because they also are designed lifetime (as per BMW), and we know there are arguments about that too. It's your car and you do whatever you please with it. :thumbup:

Well worded. I only like the 1.4 OE cap because it looks exactly like the OE 2.0. Otherwise, the 1.2 is probably a safer bet.

Another good point, If you overfill your coolant by accident, you have a bigger chance of rupturing shit with the 2.0 cap. So in reality, you can have a catastrophic coolant blow out while driving, not just shutting off.

Hey guys,

Any more update on the 1.4 BAR cap? I just ordered all the hoses, expansion tank etc and would like to use 1.4 BAR cap but wanted to see how this is going for you guys.

No negative effects. If your cooling system is tip top shape go for it

I'm fine still. I peeked in there yesterday. Coolant exactly where I filled it a bit below half. 210 mile road trip to poconos, hills galore. No issues. Well except that my pass rear door wouldnt open. But thats a different story all together.

I just had the collapsible coolant pipe installed w/ new O-rings in my '08 4.8i X5.

Coolant was flushed and replaced with Pentosin NF.

I've read that it could be beneficial to switch the coolant cap to the BMW 1.4 Bar Cap used on the 2007 335i. Any reviews on this cap or suggestions for me? Would this 2007 335i cap fit on the '08 4.8i X5?

I changed mine over and have had no loss of coolant since. before I went through 2 coolant tank ruptures and had to top it off every 6 months.

I would suggest it to all N62 v8 owners.

Good to hear man.

So did you buy the 1.4 bar cap from the 335i? I want to be clear on the exact part that I should buy from the BMW dealership

Oh you have an '06 4.8is.. Will the fit be any different on the e70 4.8i?