Among other issues, my Mini convertible 2006 will often read excessive high temperature (pinning the gauge) when direct observation of motor and radiator says otherwise.

"Pin the gauge" is unambiguous. What I mean by direct observation is that I may open the hood, and
- bring hand close to motor, with no perception of excessive heat
- place hand on radiator in front of fan (which is running) and feel no heat
- place hand on radiator at right side, away from fan, and feel moderate heat, perhaps 90 degrees F.

Coolant is diappearing, without a puddle on the ground, or is making its way into an engine otherwise starved of coolant. As much as one quart in ten miles.

Any ideas what is going on?

 

Check the thermostat housing and the expansion tank for leak.
If you sure the engine is not that hot then probably the temp sensor faulty / the connector loose / broken wire.

 

Coolant disappearing without a trace. What color is the oil?

 

1) Too much coolant was placed in the recovery tank and the system was not bled properly.
2) Recovery tank is leaking at the seam, fluid is burning off on the heat shield, if so, you will see coolant splats on the heat shield over the exhaust manifold
3) Bad head gasket

 

Recommend get a digital point-and-shoot laser temp reader; and will eliminate any doubt in determining exactly how hot it's getting, and where. Can also read places you can't safely reach with your hand.

Great for deep frying too.

 

You are overheating, the question is why. You need to check the items I listed in an earlier post. I would recommend, NOT driving and further damaging your car.

 

Thanks to all for cogent thoughts. I feel like I have a clue!

 

RedSky455
Safety Third!
Seriously, thanks for the thought. Should have been obvious to me, yet somehow I failed.

 

Just read this part. That's a LOT. As in a leak that *should* be very, very obvious on your garage floor just idling once the car warms up. Further evidence it's either the tank puking it all over the exhaust or a blown head gasket. A head gasket consuming that much coolant by itself seems like it would manifest in cartoon-level clouds of white smoke billowing out the back, if the car even runs at that point. It would also show up as oil that looks like coffee with cream in it and/or sickly sweet smelling exhaust (with burnt coolant in it).

BMW cars are infamous for cooling system weaknesses and we here in the Step Child Nation (MINI owners) are no exception. Dirty secret being, they used cheap recycled plastic in many of its parts -- a German government requirement, to 'help save the environment.'

Expansion tanks are pretty terrible across the board it turns out so +1 for the tank failing, now or soon enough to merit preemptive replacement soon. Try to pick up an aluminum one or put in a new OEM quality one to stop the hemorrhage. .

 

Did you get your problem resolved?