I have done an exhaustive search and found a few interesting things about the low-speed fan, the expansion tank, and the thermostat, but haven't found a clear cause of my own problem. Here's how it started:

Sometime about eight months ago, I had just finished a two-hour highway drive to my girlfriend's parents' house. I parked the car and waited outside for them to come back home, and while I was there the high-speed fan started running after the car was turned off. I was mortified, as it was the first time it had done this. I quickly jumped on NAM when they got home and saw that it was probably a low coolant level. The next morning, I filled it with coolant to the full line and was on my way.

Later on, it gradually got more increasing that it would run the fan after the car was turned off. I estimate that I had to fill the expansion tank with distilled H20, maybe 20oz, every three weeks. Sometimes less thatn 20oz would go in, but every three weeks nonetheless.

Jump to a couple of months ago, when I was sitting at a stop sign in my town for maybe 30 seconds, and the temperature hit the top of the gauge. My high-speed fan went on and I immediately pulled to the side of the road and turned the car off. I opened the hood, but the intercooler nor the radiator felt any more than 150°. I let the car sit about 10 minutes and then started it up to see the temperature gauge at the middle. I idled it for a couple minutes there where I was, and the gauge didn't move. I eventually drove home, passing a few more stop signs and lights, and the gauge still didn't move.

A couple weeks after that, I got to see the gauge in action. I was downtown again at a stoplight and the temperature spiked. This time I was in traffic and couldn't pull over. I was frozen for a couple of seconds before the temperature gauge plummeted all the way back down to the middle of the gauge and held there. I drove it home without another issue and checked the coolant level, which was between the full and empty lines.

Finally, a few weeks ago, I was autocrossing the car, sitting on the grid for a while inbetween my runs, and the temperature spiked again. It was slower to return to the middle of the gauge this time, but nevertheless it returned.

Yesterday was the final straw. I was idling in my friend's driveway and the temp spiked once again. It dropped fast once again as well, though, and didn't have another issue like that last night.

Here's where my questions come:

1. Is this kind of problem indicative of a temperature issue or an electrical issue? I am aware I may have a couple problems. My high-speed fan seems to come on more than usual, which could be an issue with fans or the thermostat.

2. Is the temperature gauge connected to the actual water temperature, or is it connected to the ECU, which takes information from the temperature and spits it out to the gauge? What about the high-speed fan? Is it connected to the water temperature itself, or some sort of controller that tells it when to kick on based on what the ECU says about water temperature?

3. How likely is it that I've hurt my engine with these "overheatings"? Each time it's overheated, I haven't just immediately shut the car off, but it's never illuminating the red light for more than five seconds as well.

4. Where should I start poking around? I will be checking the fans tonight, seeing if the low-speed fan comes on. And I will be taking it into the dealer for an oil change very soon as well, so I guess I'd see if there's coolant in the oil. But anything else I can check? My expansion tank is not leaking, nor do I have any leaks visible on the ground under the car. So I really have no idea where the coolant is going....which is a bad omen I think.

Any help is appreciated. Thanks!

 

Many cars have coolant tanks the leak around the seam.....and many have a leak around the thermostat....with the slow leak you have, the volume of coolant you are loosing seems about right......
Not sure about the other symptoms....if the coolant level was very low, it may have air in the system,and you may need to bleed it...
Most folks seem to be OK for a couple of overheatings....but you could still have a head-gasket fail, or warp/crack a head......I'd look at the simple stuff...and get it looked at fast before some damage occurs.

 

http://massmotoringclub.com/index.php?topic=2490.0

I think your coolant just boiled out through the expansion tank cap.....check out what happened to me. I had all your symptoms but use a scanguage II and was able to turn my heat/ac on before any over heating ocurred.

 

So on Wednesday I checked the fan with the engine running, and not to my surprise, the electric fan against the radiator was perfectly still. I found the problem...I thought.

I took it into Niello Mini for the repair and other service (inspection II), and they called back later saying, and I quote, "the reason your fan wasn't turning on was because the thermostat was bad." It would skip the low speed mode until it heats up and then turns on high speed mode."

Sorry, I don't buy this. First of all, I am pretty sure they only had time for a visual inspection yesterday (they are taking all today to work on it). Can you even test the thermostat without taking it out? Additionally, I don't buy that the fan won't turn on because of some computer knowledge that the thermostat is bad. As far as I can tell, MINI thermostats are still the simple style without any sensors attached, and should only be confirmed if bad when the thermostat is out.

Can someone confirm this? Also, can you suggest any tests that I should make upon getting the car back from repairs? I would hate to have problems even after this, as I have to use it tomorrow to drive two hours to the coast. Thanks!

 

Sounds like the techs are saying the thermostat was sticking until temps reached above 225 degrees, then opens up and temp sensors for fan assembly then kicks on high....

When you get the MINI back, let it idle in the shop and have them demonstrate that the fan is working correctly before you leave.

I ran my climate control 24/7 when my fan's resistor burned out, which is basically like turning the fan on manually. 30 seconds after turning it on, both the cooling fan and the power steering pump fan comes on together and will keep your MINI from overheating.