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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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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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  #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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  #6  
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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  #7  
Old 03-06-2013, 11:21 PM
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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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  #8  
Old 03-09-2013, 09:10 AM
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Quote:
Originally Posted by doru View Post
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.
This is what scares me when someone goes from temperature to pressure. They are in a proportion to one another, but pressure and temperature only have a certain relationship depending on the fluid. Water at 126 degrees C will have a huge difference in pressure than oil at 126 degrees C or a 50-50 mix of coolant, or a 75-25 mix of coolant. Just keep a 1.2 bar cap for what it is. Has nothing to do with temp-only pressure. You make your own assumptions as to what fluid is in the closed system and what amount of air gap exists that the fluid may expand to fill first. Cap will just vent to atmosphere at a lower pressure and that is all. If it does vent and your coolant level decreases, you have less coolant for the radiator to use to cool. Pretend you had a .6 bar cap. You would never over-heat until most of your fluid was all along the road behind you. So, the over-heating would be CAUSED by a cap releasing fluid when the pressure was too low....having NOTHING to do with temperature other than it gettinhot enough to overcome a .6 bar relief valve. Take what you said about a 1.2 bar cap holding the coolant up to 126 degrees. TYour first sentence is already making assumptions you may not have such as absolute mixture. What if your radiator was full of oil? Far fetched sure, but 1.2 cap would hold it just fine.

Last edited by 540iman; 03-09-2013 at 09:15 AM.
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  #9  
Old 03-10-2013, 09:20 AM
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Quote:
Originally Posted by 540iman View Post
This is what scares me when someone goes from temperature to pressure. They are in a proportion to one another, but pressure and temperature only have a certain relationship depending on the fluid. Water at 126 degrees C will have a huge difference in pressure than oil at 126 degrees C or a 50-50 mix of coolant, or a 75-25 mix of coolant. Just keep a 1.2 bar cap for what it is. Has nothing to do with temp-only pressure. You make your own assumptions as to what fluid is in the closed system and what amount of air gap exists that the fluid may expand to fill first. Cap will just vent to atmosphere at a lower pressure and that is all. If it does vent and your coolant level decreases, you have less coolant for the radiator to use to cool. Pretend you had a .6 bar cap. You would never over-heat until most of your fluid was all along the road behind you. So, the over-heating would be CAUSED by a cap releasing fluid when the pressure was too low....having NOTHING to do with temperature other than it gettinhot enough to overcome a .6 bar relief valve. Take what you said about a 1.2 bar cap holding the coolant up to 126 degrees. TYour first sentence is already making assumptions you may not have such as absolute mixture. What if your radiator was full of oil? Far fetched sure, but 1.2 cap would hold it just fine.

Actually I don't make ANY assumptions. It's my car, and I service it. I know what coolant I have, and what proportions of coolant/water I have. Maybe you don't know what you have in your car, but I do know what I have in mine.
And just for your info: it's a 50/50 BMW coolant/water mixture.
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  #10  
Old 03-10-2013, 01:34 PM
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540iman,
Quote:
Gary, we agree on everything, but your statement, as written in #5 is simply not true UNLESS you also include your assumptions! Really not trying to nitpick, I swear! You can't just make a statement like that..It is probably an oversight, but is really misleading as written. You must state what material you are heating to 126 Degrees C to equal 1.2 bar and how much free air space existed. If you want to say that the E39, when filled to the correct COLD level and containing a perfect 50-50 mix of anti-freeze will be at 1.2 bars of pressure if it reaches 126 degrees C then you have a possibly valid statement. I trust your math, but you can't make a statement without specifying the liquid involved and the air gap. Like you pointed-out earlier in a way-air can compress, a liquid can't. Water can only compress if it changes state; like from a liquid to a solid.
Yes, I was making the assumption of a 50/50 mix of water and OEM BMW antifreeze, filled to the correct cold level, and as measured in an m52 or m54 engine. It was a bullet point list and I didn't see the need to get much into the engineering math behind the measurements. But, you are absolutely correct.

Quote:
The single most compelling reason in my mind for the lower pressure cap is for those that over-fill their reservoir on a regular basis. Then you stress the entire system to 2 bar to let the excess coolant out so the system can return to under 2 bar. If you fill the system full, the pressure in the system will exceed 2 bar and release ONLY enough coolant to get the pressure back to under 2 bar...say 1.9 bar for arguments sake. The next time you start and run your car, the coolant level will still be too high and the pressure will likely not reach 2 bar a second time, but may reach 1.9 bar quickly and stay there, in theory, forever, or until you somehow lose enough coolant to create the proper air space.
Thank you for pointing this out as I forgot to mention it. If you over fill the expansion tank, the system can run at excessive pressures for many drive cycles, not just one.

Quote:
It is only an advantage for those who A) like the look and B) over-fill their systems regularly.
I disagree with this statement. Due to any number of reasons your vehicle can overheat. Just a few examples would be broken fan belt, bad clutch fan, bad electric fan, clogged radiator fins due to leaves or dirt, etc. In any of these situations you have ample warning via the dash display and temp gauge that something has gone wrong. I would rather the cap limit the max pressure to 1.2 bar than to have something in my coolant system explode, leave me stranded and cost me much more money.

Quote:
98-104 degrees C iirc
Correct, the m54s run a little hotter at times due to the ECM controlled thermostat which allows hotter temps at part throttle cruise conditions.


Dragan,
Quote:
Thanks for that! Now if someone would do the same for the I6.
That is what all the data from my post was taken from.
.
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  #11  
Old 03-06-2013, 08:07 PM
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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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  #12  
Old 03-07-2013, 04:09 AM
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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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  #13  
Old 03-16-2013, 05:15 AM
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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.
Robert and all,

I just found a small leak in my coolant system, this explained why I've been loosing coolant slowly. The 1.4 bar cap is not the culprit of my coolant lose.

Last edited by 16valex; 03-16-2013 at 05:17 AM.
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  #14  
Old 03-16-2013, 09:46 AM
Schitzo Schitzo is offline
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Originally Posted by 16valex View Post
Robert and all,

I just found a small leak in my coolant system, this explained why I've been loosing coolant slowly. The 1.4 bar cap is not the culprit of my coolant lose.
Thanks for the update, Alex.

It is interesting to learn that BMW has reverted to using a lower pressure cap on some of the newer cars.
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  #15  
Old 03-25-2013, 05:26 PM
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One question arose in a different thread today about the REVERSE of the venting:
Quote:
Originally Posted by rdl View Post
Radiator caps usually have a one way check valve to allow air into the system if pressure falls below atmospheric. I assume the BMW cap does too.

Keep in mind that there is always air plus water & EG vapor in the top of the expansion tank. When the system cools overnight from the temperature during the bleeding process the vapour contracts which reduces pressure, perhaps below atmospheric at which point the cap's check valve opens to allow air to enter and equalize pressure. If the check valve doesn't operate properly, the rad hose collapses. The effect would be magnified if the bleed isn't complete and there is another air pocket in the head or cabin heater circuit.

I think this effect is the reason that many people report having to add a bit of coolant the next morning after bleeding the system. Once that 2nd small fill is done the system is stabilized to ambient temperature and no further addition is needed (at least we sincerely hope
So, I ask: Does the GAS 1.2 bar cap (or the original 2-bar cap) have such a check valve?
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  #16  
Old 03-25-2013, 06:51 PM
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Quote:
So, I ask: Does the GAS 1.2 bar cap (or the original 2-bar cap) have such a check valve?
Yes, The G.A.S. 1.2 bar cap uses all brand new BMW internal components that have been recalibrate to vent at 1.2 bar, and the OEM cap has a negative pressure check valve that opens during cool down if the cooling system pressure drops below atmospheric.

Gary
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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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Old 03-07-2013, 08:09 AM
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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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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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Old 03-09-2013, 06:00 PM
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Quote:
Originally Posted by doru View Post
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.
thats right , E60 has 2 bar expansion cap but their coolant system does not fail like E39
The only complains about WP , all the rest last > 100k miles easy
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Old 03-07-2013, 08:30 AM
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Old 03-07-2013, 08:41 AM
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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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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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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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TMS underdrive pullies - Stewart WP - PSS9 - Beisan Vanos seals - Zimmerman cross-drilled & Akebono Euro - Deka 649 MF - 55w HID headlights - 35w HID foglights - Hualigan double din - ACS (rep) alu pedals - Euro central storage console - Breyton Magic Racing staggered wheels - M5 bumper - M5 steering wheel - Tint
Stable: e39, e53, e46 & Tribby
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