I have an '03 MCS with a coolant loss problem. I replaced the coolant expansion tank about 3 months ago because the old one split in the back. After filling to the max mark the tank is empty after 1-2 days. I have already checked the oil and it was not in there.

Currently coolant is visible resting on the heat shield directly bellow the tank. I have not been able to locate where it is coming from. I first thought it might be the wimpy pinch clamps used to keep the hoses attached. I replaced them with conventional hose clamps. The kind that are tightened using a screw driver. While I was in there I took the entire tank out and did inspect it for cracks in the seam. Everything looked good to me.

A theory I have is maybe the new cap is bad and is letting coolant vapors out. When is it at a light for a while after driving there is a bit of steam coming out of the hood vent directly in front of the driver seat. This could very well be the coolant on the heat shield evaporating. Is it possible however that the coolant in the tank is boiling and releasing out the cap?

Could this be a coolant brand problem? Should I switch back to mini specific coolant?

 

Doubt it has anything to do with coolant brand. While I hadn't lost that much, mine was spattering onto the heat shield below. I replaced the cap and all has been good since then. I would try another new cap and hope that's the worst of it. I'd also recommend placing some cardboard underneath when parked longterm to isolate any other leaks (e.g. thermostat gasket = common problem).

Good luck!
Greg

 

Did you overfill the expansion tank? If you did, it'll puke out the cap until the level equalizes.

 

It should only be necessary to have an inch or so of coolant in the CET (i.e. close to the MIN line). Any more and it will likely vent via the cap as Helix says. If your level stabilizes near the bottom of the CET you should be good.

 

I think I will try a new cap. It is not settling near the bottom of the cet. It is completely empty when I check it. Anyone know where I can get just the cap?

 

Last one I picked up was from Amazon 1 year ago...

 

Also http://www.ecstuning.com/Mini-2002-C...oling/ES37545/

 

I ordered a new cap yesterday. Today after I was out the steam started coming out of the vent. I opened up the hood and that stupid new tank is split at the seam near the power steering tank. I saw it sputtering it out. Looks like I will be ordering an aluminum one. Bummer I will try getting a hold of ECS on Monday to try and cancel my order.

 

happened to me and it turned out to be the water pump. about £316 to fix. Tried a local garage but they said it was too tricky so had to go to BMW directly.

 

If you still can't find it buy some ultraviolet coolant dye and pour it in. Using an ultraviolet flashlight after a few days for the dyed coolant to leak out and you'll likely find it quickly.