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Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 5 Series > E39 (1997 - 2003)

E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #1  
Old 03-06-2013, 04:33 PM
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doru doru is offline
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Got the 1.2 bar expansion tank cap from German Auto Solutions

From Gary (German Auto Solutions). It's a thing of beauty. The top is engraved steel and the relief valve is "Reutter" - the OEM supplier for the OEM expansion cap. The beauty is that "if" the temp is getting too high, it will release the pressure much sooner than the OEM cap, thus having a chance for the plastic parts to last longer. I would venture to affirm that if the cooling parts will rupture due to pressure, at a lower pressure the damage could be smaller, i.e. the crack could be just that: a smaller crack, which could allow you save the engine. At higher pressure, a crack will develop very fast in a big rupture, where one could loose cooolant very quickly.

Thanks Gary. Beautiful product.



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  #2  
Old 03-06-2013, 04:38 PM
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LaCrosse540i6 LaCrosse540i6 is offline
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Awesome! I'll be picking one up soon.
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  #3  
Old 03-06-2013, 06:28 PM
black528i black528i is offline
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I have been using the 1.2 bar cap from Gary on my car for almost two months now. No issues so far. It looks much nicer than the OEM one too.
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Old 03-06-2013, 07:26 PM
Schitzo Schitzo is offline
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The consensus over at Bimmerforums is that lower pressure cap is bad and will result in engine failure due to overheating. Are you not concerned about that?
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Old 03-06-2013, 07:44 PM
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Quote:
Originally Posted by *****zo View Post
The consensus over at Bimmerforums is that lower pressure cap is bad and will result in engine failure due to overheating. Are you not concerned about that?
Really! Don't you still have them 1.4 bar on yours Robert? I feel the 1.4 bar looses coolant too often.
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Old 03-06-2013, 08:07 PM
Schitzo Schitzo is offline
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Alex, I did not say I was part of the consensus and yes, I still run a 1.4 bar cap. going on 3 yrs now. I have not noticed issues with losing coolant.
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  #7  
Old 03-06-2013, 09:39 PM
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Quote:
Originally Posted by *****zo View Post
The consensus over at Bimmerforums is that lower pressure cap is bad and will result in engine failure due to overheating. Are you not concerned about that?
No.
Because the 1.2 bar cap holds the coolant pressure up to 126C or 260F. If you ever reach that temperature, chances are your engine has or starts to overheat. And if you reach that temperature, something else is wrong, not the expansion tank cap.
For example, I know 100% that if I see the KTMP going past 98C, one culprit could be a bad fan clutch. And with a bad fan clutch I noticed KTMP as high as 102C. Which is still below 126C. I adressed the issue, the KTMP stays where it should be now. That's for i6. For v8 the normal operating temp is higher.
So, yes, I think it's pretty safe. Thanks for pointing it out though. One can never be too careful.
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  #8  
Old 03-06-2013, 11:21 PM
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bluebee bluebee is offline
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This is a nice thread to cross reference with the following (found by typing /cap F3 in the best links):
- All about modifying the cooling system pressure cap (1)


EDIT:
Quote:
Originally Posted by doru View Post
noticed KTMP as high as 102C. Which is still below 126C.
I know Doru is aware but for others to reference, normal KTMP fluctuations are discussed, in detail, in this thread (found by typing /thermostat F3 in the bestlinks):
- What is the temperature of the coolant & when the thermostat opens under normal conditions (1)
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Last edited by bluebee; 03-06-2013 at 11:30 PM.
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  #9  
Old 03-07-2013, 04:09 AM
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16valex 16valex is offline
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Quote:
Originally Posted by *****zo View Post
Alex, I did not say I was part of the consensus and yes, I still run a 1.4 bar cap. going on 3 yrs now. I have not noticed issues with losing coolant.
Oh, that's good, at least we're on the same page. I don't see how a lower pressure cap is more vulnerable to over heat, to my knowledge it would help the situation. Thanks for the clarification buddy.
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  #10  
Old 03-07-2013, 07:13 AM
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Very lengthy and technical discussion on the M54 engine here:

http://forum.e46fanatics.com/showthread.php?t=948548

I myself will get the E30 1.4 bar cap.
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  #11  
Old 03-07-2013, 08:09 AM
esilvas esilvas is offline
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I also ordered one of the 1.2 bar caps from German Auto and can't wait to get it in my car. But, remembering some of my college chemistry, I don't think it will result in increased overheating. It would probably increase the likelihood of overboiling, i.e. coolant out of the radiator cap due to the lower pressure. But, the coolant would still have to reach a certain temperature before that could happen. In this case, the 1.2 bar cap is still above 1.0 bar or sea level pressure and would work (like the 2.0 bar cap) to prevent overboiling.

Also, the point of antifreeze/coolant is to both lower the freezing temperature and increase the boiling temperature. It just seems like the new 1.2 bar cap will work. Still, there must be a reason BMW is using a 2.0 bar cap.

I will update my experience once I have replaced my current cap with the one from German Auto.
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  #12  
Old 03-07-2013, 08:23 AM
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I think BMW did a mistake with the 2 bar expansion cap, and fixed it on the newer BMW models to 1 bar expansion caps to prabably avoid the catastrophic cooling system failures (ruptured radiator necks, split expansion tanks to name a couple). Pretty much for the same engine (N52 vs M54 - not much different).

Edit: The above statement is wrong. The source I quoted was off.
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Last edited by doru; 03-07-2013 at 08:51 AM.
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  #13  
Old 03-07-2013, 08:30 AM
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  #14  
Old 03-07-2013, 08:41 AM
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German Auto Solutions
Black one is $34.95, red one is $36.95.
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  #15  
Old 03-07-2013, 09:39 AM
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If you choose the lower pressure cap, make sure the expansion tank is topped to the LOWER LIMITS.
Quote from the "Fanatics", real-life test:

Originally Posted by kmulder
Hello everyone,

We've done extensive testing on this subject, and wanted to share some of the results. For testing, we used a 1997 E39 at idle in a garage. The main radiator fan was removed, and the auxiliary fan blocked off in order to force the system into higher temperatures and pressures. We first tried with only the main fan removed, but the auxiliary fan was successful in preventing the temperature from rising above 103 degrees C. It would turn on at 103 C and lower the system temperature to 95 C at which point the fan shut off again. We monitored coolant temperature both through the on-board diagnostics and through external software. Each test began with everything at ambient temperature. The expansion tank was tapped and a low-pressure gauge installed to monitor the pressure in the expansion tank.

Results:

We saw a maximum temperature of 126 degrees C (~260 F) before ending the test. We were unable to increase the temperature above this due to the efficiency of the system even without airflow. Keep in mind that a 50/50 mix of coolant will boil at approximately 135 C (275 F), so we were very close. Pressure at this temperature (126 C) was 20.5 PSI. The temp gauge needle was in the red zone well before this and the coolant temp warning light was on. Pressure never increased above 15 PSI before a temperature of 120 degrees C. We ran the test several times and achieved virtually identical results each time. We also tested the system with purposefully low coolant to see how that would affect the results. At a given coolant temperature, the pressure is lower in a system with low coolant.

During normal operating conditions, the system never operates anywhere near 2 bar. Assuming normal operating temps of 105 C (a bit on the high end), the system won't see pressures above 10 PSI.
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  #16  
Old 03-07-2013, 09:43 AM
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Quote:
Originally Posted by doru View Post
the pressure is lower in a system with low coolant
I'm struggling with understanding all this.

Is it two things we should do?

One, keep the coolant lower (within limits) to keep the pressure lower?
Two, use a lower pressure cap so that it will vent before the radiator blows?
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  #17  
Old 03-07-2013, 10:21 AM
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Quote:
Originally Posted by shaftdrive View Post
I'm struggling with understanding all this.

Is it two things we should do?

One, keep the coolant lower (within limits) to keep the pressure lower?
Two, use a lower pressure cap so that it will vent before the radiator blows?
I think the 2 bar cap was designed to be "foolproof", as in some people overfill the cooling system (the expansion tank gauge at cold sits high). In this case, there is little room for expansion. If the coolant temp is too high, you would develop higher pressure (this leads to the much documented expansion tank cracks).
The high pressure ET cap is a good thing if you track the car, where you have high rpm's in lower gears steady. My car is a DD, and very seldom sees 4-5k rpm's, so the pressure-cooker ET is useless to me. On contraire, it's a ticking bomb.

Quote from the "Fanatics":

Originally Posted by SeanC
Just did a quick calculation. Apparently 1 bar cap is good enough. Take it for what it's worth:

Assuming 96 degree Celcius coolant temperature, which is pretty much the max, the pressure of an ideal gas (e.g. air) is 1.3516 atms. That means you'd need a cap capable of holding 1.3516 bars at the minimum. This would be called a 0.3516 bar cap. This would, however, increase the boiling point of the coolant by a mere 8.5 degrees (Celcius):

So %100 water as your coolant would boil at 108.5 degrees Celcius instead of 100 degrees.
%50-%50 mix would boil at 114.5 degrees Celcius instead of 106.

These numbers are ok theoretically, but they are too close for comfort in real life. Locally, temperatures could be higher than these (e.g. engine block), and your coolant will turn into gas whenever this occurs. Since gas occupies more space than liquid, you'd be replacing your hoses quite often. I am assuming the engine block can take a beating.

On the other hand, 1 bar cap increases the boiling point by about 24 degrees Celcius. So for 100% water, you'll get 124 degrees Celcius as your new boiling point. For 50-50 mix, it will be 130 degrees. Similarly, 2 bar cap raises it by 48 degrees, so your new boiling points for 100% water and 50-50 mix will be 148 and 154 degrees, respectively.

Since the operating temperature of your engine doesn't change, using a 1 bar cap will lower your chances of blowing the head gasket. You'll probably see your car smoking before the temp gauge hits the maximum. But there is more chance of introducing excess air (gas) into the system, which could require you to use heavy duty hoses in lieu of what comes from the factory.
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Old 03-07-2013, 10:36 AM
mifesto mifesto is offline
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people here dont understand the cap doesnt cause pressure, the heat does. heat is produced and maintained by thermostat opening and closing to route water to the radiator. rad cap is simply a safety device to allow pressure to escape if necessary. venting in a car ejects precious coolant and introduces air into the system; this is NOT the solution to lower pressure. lowering temperature is the ONLY way to reduce pressure of a ethylene glycol/water mixture. this total failure of people's understanding may be especially bad for the 540is(as they run hotter) and hit that 1.2 bars sooner then the i6 guys.

Last edited by mifesto; 03-07-2013 at 10:43 AM.
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Old 03-07-2013, 10:55 AM
Dragan Dragan is offline
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Has anyone actually had a pressure gauge hooked up to the cooling system in the following conditions:

Idling when cold

Idling at operating temperature

at 2500 rpm with fan blowing air through rad to simulate highway cruising

I'd be curious to see all the pressure readings under these conditions.
And another thing that hasn't been clarified, is the 2 bars of pressure gauge or atmospheric? I assume it's gauge since that's how we measure everything else (tires, fuel pressure, etc.).
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Old 03-07-2013, 11:38 AM
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doru doru is offline
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Quote:
Originally Posted by mifesto View Post
people here dont understand the cap doesnt cause pressure, the heat does. heat is produced and maintained by thermostat opening and closing to route water to the radiator. rad cap is simply a safety device to allow pressure to escape if necessary. venting in a car ejects precious coolant and introduces air into the system; this is NOT the solution to lower pressure. lowering temperature is the ONLY way to reduce pressure of a ethylene glycol/water mixture. this total failure of people's understanding may be especially bad for the 540is(as they run hotter) and hit that 1.2 bars sooner then the i6 guys.
Never said it reduces pressure in the cooling system.
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  #21  
Old 03-07-2013, 12:20 PM
mifesto mifesto is offline
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no but many are mislead to believe a lower psi cap will help when infact it will either not help or endanger your car of overheating from lack of coolant.
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Old 03-07-2013, 12:27 PM
mifesto mifesto is offline
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Quote:
Originally Posted by doru View Post
The beauty is that "if" the temp is getting too high, it will release the pressure much sooner than the OEM cap, thus having a chance for the plastic parts to last longer
...but your statement here may not be correct. in a rice cooker, releasing pressure is fine. in a automotive cooling system, releasing pressure sooner also releases coolant(and introduces air), which actually will force the engine temp to rise even FASTER. in an overheating scenario, shutting engine down(and breaking the cycle of heat production) is the only way to stop it.
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Old 03-07-2013, 01:20 PM
Mikes530 Mikes530 is offline
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Having read most of the e46fanatics thread and other posts here and elsewhere, I have one question which I haven't seen answered directly - why did the BMW engineers decide on a 2 bar cap in the first place? As noted in previous posts, testing under extreme conditions couldn't get the coolant temp above 126 deg. A 1 bar cap will bring the coolant boiling point up to 130 deg and a 2 bar cap will raise it to 154 deg. The cap has two primary functions - to pressurize the system and to act as the "weakest link" if over-pressurization occurs. So what scenario were the engineers seeing when they decided on a 2 bar cap?

I took a quick look at two ends of the automotive spectrum and found:
Toyota Corolla average 1.2 bar
Ferrari (a couple of models) 0.9 to 1.1 bar

From what I can gather, 1.1 to 1.2 seems to be an industry norm. This seems to be independent of the use of plastic or aluminum radiators. Perhaps someone knows of exceptions? It's doubtful that BMW engines are sufficiently unique to warrant such a departure from industry norms.

BMW has been known for missteps - lifetime tranny fluid (although this might have been driven by marketing), vanos seals, the truly horrible design of the CCV system etc. Could the 2 bar cap be another?
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Old 03-07-2013, 02:17 PM
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I know the e30 had the 2 bar cap, and BMW backed off to 1.4 bar cap a few years back. Guys posted it on the other forum.
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  #25  
Old 03-07-2013, 11:01 PM
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Quote:
Originally Posted by doru View Post
If you choose the lower pressure cap, make sure the expansion tank is topped to the LOWER LIMITS.
Quote from the "Fanatics", real-life test:

Originally Posted by kmulder
Hello everyone,

We've done extensive testing on this subject, and wanted to share some of the results. For testing, we used a 1997 E39 at idle in a garage. The main radiator fan was removed, and the auxiliary fan blocked off in order to force the system into higher temperatures and pressures. We first tried with only the main fan removed, but the auxiliary fan was successful in preventing the temperature from rising above 103 degrees C. It would turn on at 103 C and lower the system temperature to 95 C at which point the fan shut off again. We monitored coolant temperature both through the on-board diagnostics and through external software. Each test began with everything at ambient temperature. The expansion tank was tapped and a low-pressure gauge installed to monitor the pressure in the expansion tank.

Results:

We saw a maximum temperature of 126 degrees C (~260 F) before ending the test. We were unable to increase the temperature above this due to the efficiency of the system even without airflow. Keep in mind that a 50/50 mix of coolant will boil at approximately 135 C (275 F), so we were very close. Pressure at this temperature (126 C) was 20.5 PSI. The temp gauge needle was in the red zone well before this and the coolant temp warning light was on. Pressure never increased above 15 PSI before a temperature of 120 degrees C. We ran the test several times and achieved virtually identical results each time. We also tested the system with purposefully low coolant to see how that would affect the results. At a given coolant temperature, the pressure is lower in a system with low coolant.

During normal operating conditions, the system never operates anywhere near 2 bar. Assuming normal operating temps of 105 C (a bit on the high end), the system won't see pressures above 10 PSI.
This seems good information. If combustion gas isn't getting in, then the cap doesn't make a difference, it's only a pressure release if a problem. If combustion gas is getting in i.e. cracked head, then the pressure will go the limit regardless of engine or coolant temps, and then a lower bar cap may help by not overpressurizing the system and getting a burst.
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