Hi all, I have a few older threads about my cooling system troubles, but here is a summary.
I am getting air in the system, but only under load\boost. Zero leaks ( was pressure tested)
Car can sit at idle or gentle drive keeping rpms low and not over heat. But if I do heavy acceleration, within 30 sec my heat coming out of the vents will go cold, temps will spike, and bubbles are visible coming up in expansion tank.
I have replaced water pump, friction wheel, thermostat on my own..no external leaks, but could not resolve problem.
I thought ok maybe head gasket, but I have no mixing of oil\coolant anywhere, bought one of those combustion gas testers with the blue liquid, test was negative.
Ok the next step is a real kick in the a$$..
Took car to BMW dealer (no mini dealer here)with the same symptoms..they replaced thermostat again said the one I installed was defective.
Then gave me the car back, problem was still there, took it back..they replaced expansion tank..gave it back, stills same problem, then they wanted to tow it 2hrs to a mini dealer, that is when I said no way and got the car back.


So.. is there any way for air to get sucked in via turbo cooling system when under boost? Can it be a cracked cylinder? or head gasket that only pushes are into cooling system under load?


Please any suggestions, it is sitting in my garage and I have no idea what to do next.


Thanks.

 

This happened to me, it ended up being the expansion tanks pressurized cap which when it no longer is able to hold pressure you'll get air bubbles at first and then the expansion tank will start to overflow. Same thing will happen to a radiator cap once it no longer is able to keep the cooling system pressurized.

I mean if you have ever seen a radiator cap unable to hold pressure you simply replace it, it's astonishing the dealer couldn't figure it out. BMW/Mini dealers are clueless about their own cars, sad!

 

Thanks systemlord, but the expansion tank and cap were replaced already.
My thinking is the bubbling in the expansion tank is causing the coolant to rise in tank and blow out the cap. Are they set to release at a certain pressure as a fail safe?
Maybe I should try replacing the cap again?
Any other suggestions?


Thanks.

 

The turbo does have coolant lines to cool the compressor section. I suppose it is possible for air infiltration under boost.

I doubt that it is anything with the engine itself. The pressures in the cylinder are orders of magnitude greater than the minuscule 15 psi from the turbo.

Do you happen to have the cold weather intake manifold?

 

Any idea how air from turbo cooling system can get in? Aside from the coolant lines, which there are no leaks is there a gasket in there somewhere?


And yes I believe I do have cold weather intake manifold.?


Thanks,

 

I don't know first hand how the coolant seals inside the turbo housing are arranged. But my thinking is that the 15 psi or so of boost could be just enough to push past worn seals or o-rings especially if there is excessive play in the shaft.

Again though, I'm not sure if this is physically possible, depending on how the seals are arranged.

Regarding the cold weather intake, I'm not positive how it heats the throttle body. It uses either coolant or air from the intake tract itself. If it does use coolant then this could be potential source of trouble.

 

I first started noticing air bubbles in my expansion tank, after a while the coolant started boiling over out the pressurized cap. Once I replace the cap all was back to normal. It's possible you got a bad cap and is the least expensive option.