Strange Problem......
After a long run the water temp gauge goes to max - but everything appears ok - although the heater stops putting out warm air.
When the the engine is warming up the heater is set to Auto - it seems to think that it is pumping out hot air (after about 2 minutes the heater comes on) but it's putting out cold air.
The other intresting thing is that I can be sitting in traffic with the temp gauge at normal, and the heater is putting out cold air - when I accelerate again it starts putting out hot air again.
Also sometimes it seems to put out scalding hot air as opposed to the required temp..
Could the water pump be 'lazy' or on the way out..I've had the sensor changed but not the sender unit.
Everything else seems to be ok - even when it is supposedly boiling over..
Any ideas?
Cheers
Michael
STI3 5dr

 

Could it be the thermostat?

 

Could you have an airlock in your cooling system