So ive been reading to find the answer to my problem. I noticed that faulty thermostats was a pretty common issue which leads me to my problem. I have a 2005 mini cooper non S. I started noticing the heat blowing cold then kicking back in sometimes. Also the temp gauge goes up real high like in the red a few times. It only did this when idling at first which made me believe a stuck thermostat. Now it will do it when driving in certain conditions. when i shut the car down after driving the fans run for a while but eventually shut off. My car is out of warranty and i live in Buffalo, NY and i need heat. Im pretty handy with replacing parts on cars but not always so good at diagnosing so all help is greatly appreciated.

 

anyone?

 

First things first, have you checked the coolant level in the system. If its low it will do the hot and cold from the heater. Be sure to check both the expansion tank and the actual system.

 

Tanner55, I think you've been driving my car! I have had the exact same problem recently, and was reading up on posts about cooling / thermostat issues.

Initially my overheating issue was also just at idle, but progressed to become an intermittent issue at highway speeds. There did not seem to be any particular combination of travel time, speed, etc that would make the temp start to rise, which made me think the thermostat was faulty. The high speed fan would stay on after the car was shut off, but I did not problem with the fan never shutting off and killing the battery, like many other have posted about.

So last Sunday I checked the expansion tank, and it was empty, so I filled it back up. I drove for a couple days, checking the expansion tank level, and it stayed right at the point I had filled it to. It didn't occur to me to check the actual system level until mylittlemini suggested it, mostly because it doesn't say anything about the system level in the owner's manual (I suppose I'm an idiot and need to get the shop manual!)

So, Wednesday night I take off the radiator cap and see - nothing. Thursday morning before work I go to fill the system and lo and behold the expansion tank is empty and the system has fluid in it.

So to summarize, I think in my case, and maybe yours, the valve on the radiator cap might be sticking, essentially becoming a one way valve, allowing fluid up and out but never back in, and eventually it's all (or mostly) gone.

When I opened the radiator system cap the first time I think it jiggled the valve on the cap and allowed to it work properly and pull enough vacuum to pull the fluid out of the expansion tank. I will be replacing that cap today, however, as I am told they are relatively inexpensive.

And now that the coolant level is back to nominal, the overheating has stopped and the cabin heater actually blows hot air again.

 

Overheating too!
MC '03
Mechanic says I need to replace radiator, thermastat, etc for $1300
He said there was a leak that resulted from a crack in a plastic part (I was 1/2 asleep when he called).