Been having an issue with my wife's cabrio, and wanted to get other members' opinions. First - it's a used 2007 Cooper S.


The day after we bought the car and brought it home in early May of this year, it ran hot. Temp gauge fluctuated, but pegged a few times, while sitting still. Rushed the car home, and I began checking things over. As most everyone would do first, I checked the coolant overflow tank - COMPLETELY EMPTY! No problem - got antifreeze in the garage, just fill it up. Worked fine - no more overheating issues and temp gauge registered correctly - for about 2 or 3 weeks.


Then, my wife calls me at work and tells me the car ran hot again. My first thought... what the hell is going on here?! I checked the car over and this time - "looked" for leaks. None to be found, or at least not any leaks that I could see, or find! I remember reading somewhere, that there was an issue with the 1st Gen.'s having a coolant overflow tank leak problem. So, I checked the overflow tank carefully. Can't "see" any signs of a crack, a leak, or for that matter, even any evidence where there might have been a leak, leaving behind coolant residue. Can't see any leaks around the radiator, and there's - NOT A DROP - of coolant on the pavement in our driveway. Don't even "smell" coolant, like you normally would with a leak!


Here's the issue...
I've now filled up that coolant overflow tank - 4 TIMES since early May!!! With that much "added" coolant - if there were a leak - you would certainly think you would "see" evidence by now somewhere, especially on the driveway?! But so far - NOTHING! In fact, a couple of Saturdays back, I had the car up on jacks, to change the brake pads and brake pad sensors, and didn't see ANY evidence of a possible leak "under" the car either?! So where the hell is all that coolant going?! If it were a head gasket issue, with that much leakage, there's NO doubt you'd "see" white smoke coming from the exhaust - even at the very least - a rough running engine! But this little thing is running like a champ and hums beautifully at idle!


I'm literally baffled by this?! Any thoughts or ideas, would be greatly appreciated!

 

I'd bet that the thermostat housing is leaking. It is a common failure point.

 

Even then, wouldn't you "see" evidence of leakage somewhere?!

Where exactly is the thermostat housing located? If you can offer me a location point, I'll check it and let you know.

 

Or even a radiator issue....or a pinhole in a hose...radiator or heater..
Look around for residue...coolant usually leaves a crustly residue where it leaks...looks like dried road salt...

 

As much antifreeze as I've put in the car since May, it seems like it would almost "have" to be larger than a pin hole?! Even if that were the case, by now, I should certainly "see" some kind of evidence on the driveway!

 

A thermostat housing leak tends to get "blown" back....and not leave drips....
Look around the airbox (if you still have it, rather than a CAI)...look...smell...very common issue.
Also there is a oil cooler with a coolant loop....you can see it from above the pax side motor mount or the well...down low...be sure that is dry too.

 

Being new to the Mini family, I'll assume the CAI is the opposite of a box that would hold an air filter. Mine has a mesh-like top, with a plastic housing. Is that considered a CAI?

The oil cooler I should be able to find. From your description, it sounds like it's close to the oil filter on the car. I assume the well, is the space in that localized area.

Sorry to be such a dumbares!