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Another cooling system problem

OK, i have read through as many previous threads as possible to try and figure this out myself, but to no avail. my problem is that there is a high build up of pressure in the cooling system. this started after flushing out the system. the thermostat is ok, the fans come on at the right time, and the pump hasn't seized. i have driven the car enough to know that the hoses aren't on the brink of explosion though. the car does not overheat a single bit, even in stop and go traffic. this has me thinking the head gasket is going south. (no smoke on startup either) can someone tell me if i'm on the right track or if there's something else causing the buildup. i don't want to keep driving the car if it is the gasket. more info available if required.

the more opinions/suggestions the better!
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Old 10-15-2004, 08:07 PM
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where is the pressure seen?
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Old 10-15-2004, 10:49 PM
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Is your radiator cap OK? I'd replace it if its old and see if your problem goes away.
Old 10-16-2004, 04:18 AM
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Yeah...Where is the presure seen at?
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Old 10-16-2004, 06:14 AM
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it has build up everywhere. in all hoses and the reservoir. if the cap were to be bad, how is it able to hold in all that pressure?
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Old 10-16-2004, 09:40 AM
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maybe the radiators plugged.
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Old 10-16-2004, 08:33 PM
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Have you bled air from the system? Does the fluid level in your reservoir drop when the engine is running? I've seen systems where the head gasket leaks forcing an overpressure in the system. As the hoses are the weakest member of the cooling system, they expand and, hence, the level in the reservoir drops.
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Old 10-17-2004, 03:12 AM
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i have bled the darn thing many times and there just isn't any more air in there. i don't think the fluid drops when the engine is running but i'll check more closely. i think i will try a new cap first and see if that doesn't do anything.
and i don't think the radiator is plugged because the system is cooling like it should.
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Old 10-17-2004, 03:15 PM
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Someone out there will correct me on this if I'm wrong but I believe that the radiator cap functions to keep the pressure right for your car/application. The cap can leak, or, not let pressure out to the overflow tank---therefore over pressure. If it gets too high I'd count on blowing a hose or worse.
Old 10-17-2004, 04:33 PM
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thanks newoldguy, now i will definitely get a new cap and see if that works. thats new info to me and thats what i've been waiting to hear. i hope you are right on that. if not, i hope someone will let us know.
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Old 10-17-2004, 06:39 PM
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Porschefreak:

Why do you think you have a problem?

What makes you think that there is a high pressure build-up?

What do you consider "high"?

What pressure rating is the rad. cap?
Old 10-17-2004, 08:06 PM
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the pressure relief is the cap's rated pressure in foot pounds. looks like there is a cap for the early model 944 and the later model, according to pelican parts online catalog.
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Old 10-17-2004, 08:29 PM
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speed:

Foot-pounds is "TORQUE" - as in: "you tighten your wheel nuts to 94 foot-pounds"........

Radiator caps are in calibrated for "PRESSURE" - as in: "POUNDS PER SQUARE INCH"......

If you don't know the answer, PLEASE don't guess...........

Last edited by GUMBALL; 10-17-2004 at 08:59 PM..
Old 10-17-2004, 08:55 PM
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How do you know the pressure is high? What is your coolant ratio, that is amount of water to amount of antifreeze?
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Old 10-18-2004, 03:09 AM
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i know the pressure is high because the reservoir is bulging and all the hoses are a lot firmer than they should be. the cap is 150 psi.(original German part) i have a 50/50 ratio mix.
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Old 10-18-2004, 09:33 AM
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It is NOT POSSIBLE that you have a 150 psi rad cap.

If it is European, I would guess that it is either 1.5 Bar (atmospheres) or 150 kPa, which would make it about 22 psi.

That is not overly high - the reservoir (being plastic) will take on a mild bulge over time, and the hoses at 22 psi, will feel hard.

And for the cooling system to work properly, it MUST build pressure as it comes up to working temperature.

It is possible that the cap is not releasing - if in doubt, just replace the cap. I don't know what the factory spec is, but I would guess at somewhere around 15-20 psi. The parts retailers (Pelican, Napa, Autozone, etc.) will have the spec in their parts books.

From what you are telling me, you DO NOT have a problem.....relax and enjoy the car.

Last edited by GUMBALL; 10-18-2004 at 02:10 PM..
Old 10-18-2004, 09:52 AM
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thats right, it is 150 kPa or 1.5 bar not psi. i will get a new cap and reassure myself that there is no problem. thanks for the help.
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Old 10-18-2004, 01:38 PM
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Old reservoirs bulge out a bit.
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2011 528i
Old 10-18-2004, 02:31 PM
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