Cooling System Problems: What do I look for when buying?

Post four for this newbie; I promise no more for today after this. Also, thank you all for the feedback on my other posts. To recap, I am switching from polishing up 1980s Volvos to mid '90s BMWs and am
trying to learn all I can before I make the purchase of a '91-95 5er E34.
I've heard BMW has something called a 'Pressurized Cooling System.' I do not understand this term. I am familiar with cooling systems that have a pressure sensitive radiator cap, like the old days, to let off steam. My Volvos do not have radiator cap, instead the reservoir cap is the same. I've tried searching this forum and Googling, but cannot find an overview explaining the details of how the system works.
Why this post? I'm reading a bimmer forum (http://www.bimmer.info / forum/showthread.php?t435&highlight=overheating) and this guy has a heating problem in which his headgasket is about to be shot and white smoke is about to come out of the pipes.
It has not YET. What if I am looking at a car that someone has, with a similar problem, and they try and dump it before the obvious signs appear. How do I test for this? Is there a good way to know if a car is about to suffer some head gasket damage or failure?
Please advise. Many thanks!
Jamie
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AFAIA all cars have pressurised cooling systems. Usually done by having a pressure relief valve in the radiator cap. Set to release at around 1 bar. Pressurising the cooling system raises the boiling point of the coolant, because at atmospheric pressure, the ideal running temperature for the engine is near boiling point. Around 180 F if memory serves, and the boiling point is reduced at any sort of altitude. Mike.
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I was curious about this because the way I heard the conversation one time, it was something unique to BMW. So I'm thinking it's like an Air conditioning system or something. Some complex system where you don't just open a cap, add coolant and move on. It sounded like you seal shut the system and if you break the seal you have to do something special to re-pressurize it.
The only pressurized system I know of is when a cooling system gets hot it builds pressure until either something gives relief or you blow something.
Is BMW different?
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JamieB wrote:

No.
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Nothing as sophisticated as that. I don't know of any car cooling system that works in that way.

Prexactly. That's the way they work. If the pressure exceeds the setting of the cap, it releases it. Switch off and as the engine cools, the pressure drops down to atmospheric. Mike.
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Very slightly. In most cars, the place where you add water or coolant is not pressurized. However, where you add water to a BMW is pressurized; hence you need to wait until the car cools down before checking the coolant level.
In this regard, BMW is not greatly different from cars of days gone by.
Jim
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Not in any car I've ever owned. There's not much fundamentally different in BMWs than in any other car. People often seem to think they're they're unique in some way but it's just not the case.
I took a look at the posted thread and couldn't understand why the guy was pressurising the system. I guess he wrote it by mistake or meant something else, or had a pressure check system on hand.
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