Cooling question?

[ArtMan]

Originally Posted by trader4

I haven't analyzed the coolant recovery system in the X5, but in
every other car I've seen, as pressure in the system builds and
exceeds a set pressure, the cap allows the coolant to go into
a coolant reservoir. It doesn't leak out from the cap and wind up
on the ground. And then when the pressure lowers when the car
is off, the coolant flows back from the reservoir into the cooling
system.

The thermostats aren't exactly electronic. They are mechanical
with a resistance heater added. In the wisdom of the geniuses
at BMW, that complication allows them to run the cars hotter
most of the time. But under extreme conditions, ie very hot
ambient, towing, etc, that could allow the engine to get too hot.
So, under those cases, the computer turns on the little heater
in the thermostat, which forces it to open early. If your thermostat
was failing, you'd very likely see other symptoms, including
the temp gauge rising. Yeah, it's not 100% accurate. But BMW
obviously thinks it's accurate enough that it's worth putting on the
dash. And I've never seen a failed thermostat that caused a car
to overheat with the temp gauge still showing normal. Not on BMW,
not on any car.

Given that you now say you've also seen white smoke on occasion,
I agree that the head gasket is a possibility. But again, I'd first
focus on what's clearly not right, which is that coolant is somehow
coming out from the cap. I don't see why you want to just ignore
that, which is the most obvious thing.

Im not ignoring im just building a list of things to check not just one but a list ie brainstorming and i appreciate any and all feedback and ideas trader4

i dont want to check one thing come back chit chat go back check i want to have a list of stuff to look though and inspect.....

so i have a the older cap and i ll grab a new cap as its cheap insurance to see fi that helps

however like i said before why i dont think the cap is the problem is becuase how the upper hose balloons up its out of norm and im thinking its the head gasket but ill check the cap and do the combustion test


ive dont a compression test and while numbers were not off the chart they were ok for a 200K engine and i did my best to do a leak down test and i had moderate leakage in the crankcase so the rings which is another huge issue with bmws use of low tensile rings in the m54 engine its well documented issue......