Overheating 2 months ago I replaced the thermostat. at first it fixed the problem. 15 mins at idle it would start throwing cold air. then heat etc the other day at an accident (not mine) my cpu told met it was hot. 25 mins at idle. check engine light came on, trunk ajar came on, Any ideas.

I think I answered this already, but just because you installed a new thermostat does not mean it is good. Sure sounds like a thermostat issue.

If the thermostat is bad (i.e. stuck open at all times), this would allow coolant to circulate in the engine even when it is below the desired operating temperature. This leads to OVERcooling of the engine. You can either replace the thermostat as a first step or remove it and test it -- closed when cold, open when heated above 190-200F.

sounds like the radiator is blocked either coolant flow or ext air flow through the matrix the thermostat can get ruined when the system overheats so allways change the stat after a overheat problem GET THE RAD CHECKED FIRST if ok check the coolant pump

I have to believe that your thermostat is still sticking....replace it and you problem should go away. Relatively inexpensive fix.

Chanches are it is probably the fan. Anything over 15 miles an hour the fan is no longer needed. I would get a cheap hydrometer and make sure your antifreeze is still good.

unfortunately these engines are known for this condition and for head gasket failure.with engine cold pressurize cooling system with spark plugs removed.look down into holes with flashlight after about ten minutes.....im betting youll see a puddle of coolant on piston...usually its cyl# 2 or 3.i cant think of any other possibility for system repeatedly airlocking other than a head gasket.good news they are probably one of the easier ones to replace.

I'd still check the thermostat. Or basically just replace it. Have you ever drained all the antifreeze and flushed the system? Good time to do both. If the hose's get real hot that doesn't really mean the thermostat open. Wouldn't they get hot even if the thermostat didnt open.? If the thermostat was stuck open you'd would have cold air and low temp gauge. Then maybe hit a pump or something and have the thermostat stick closed and have high temp. Maybe water pump. Check it when you have the belt off. Spin, pull & push the water pump pulley around. I'd replaced my water pump at about 110,000 on a '97 dodge Dakota. My 97 never had a very good heater. Always heated up more after driving. Idle never got it warmed up.

Clarence,
your mini-cooper may just need a new thermostat. if the thermostat in your car is the original, then 4 years is a goodly amount of time for any thermostat to last. Thermostats fail in 2 ways: (A) stuck open, which causes engine to warm really slowly, and (b) stuck closed, causing overheating and
causing the heater to blow cold air - since the heated coolant can't get past the closed thermostat to
circulate through the heater core (a small radiator-like device used to heat the interior of your car).
Your car's thermostat has failed in mode (B).
Your cost: $5-$15 at any auto parts store.
Project complexity: any handy person could teach themselves to replace a thermostat.

It sounds like the the thermostat that was replaced is probably faulty. This being the cheapest and easiest to do I would start there. I can't reply about the air pockets. I have never heard of that before.

2000 jetta warms up when idling, but gets cold as soon as I start driving.