I have an 03 Mini with about 82k miles. runs well, but I am slowly losing coolant from the expansion tank. I forgot to check it for a while and then had an overheating problem, but bled the system and no more overheating, but the expansion tank eventually emptys out. I can not find any signs of where its going and we did a check with about 15lbs of pressure and couldnt see any leaks. Any ideas what to check?

 

look at the thermostat housing to the side of the head.
you might see some dried up coolant

ps; i just noticed you posted the same thing twice, please don't do that again its really annoying!!!

 

Lighten up Joey. After all it's only his 1st or 2nd if you count his duplicate post.

 

nothing in the oil? runs good? heat shield over header have dried coolant? could be crack in tank (common) . no white smoke once warm ?

 

My 2003 MCS (120,000 miles) started having the same problem. It also started "revving" when at idle. Check your oil. My oil has water in it which indicates a bad head gasket. Will be changing it out soon. Hopefully your problem turns out to be less "painful".

 

The thermostat housing is a known issue: mine was replaced under warrantee. If there is fluid on the ground under the center-front of the engine, it's the most likely candidate, and should be a fairly cheap fix.

 

I was getting the "slow drip" spot on my garage and found it to be the thermostat housing. Mine is an '03 S with 62,000 miles. It seems like the 60-70K mark is the range for most replacements. The replacement was $50 from Mini (including new thermostat), which wasn't nearly as much as I thought they'd steal from me. It took me about 2 hours to replace and was relatively easy. The hardest part was pulling/reinstalling the hoses because of those silly spring type hose clamps. Cars have been built for 100 years with screw type hose clamps, why do we have to reinvent the wheel ? I also find it incredibly frustrating that Mini would choose a plastic housing instead of another material. Oh well, I guess no car is perfect.

 

On the MCS check the oil cooler under the oil filter housing. They are leakers with age and will mix water into the oil, cheaper fix than head gasket.