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?t=13435&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

"JamieB" <jamiebabineaux (AT) gmail (DOT) com> wrote

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.

On Mar 29, 2:23 pm, "Mike G" <met... (AT) lycos (DOT) co.uk> wrote:
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?

JamieB wrote:

No.

"JamieB" <jamiebabineaux (AT) gmail (DOT) com> wrote

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.

"JamieB" <jamiebabineaux (AT) gmail (DOT) com> wrote

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

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.