I've taken the coolant thermostat out to test it - it opens at around 90deg, and will close in cool/warm water, so I'm sure it's working....
Starting from cold, the 'water temp' needle will climb to 90-95, then obviously the therm opens and it seems to plummet the temp to 80 (or below - that's as low as it goes). Then it never heats up again?
I've previously replaced the therm as it was stuck open, but that's not the case now (as it does heat up?)
It seems it doesn't close when it should??
Maybe it's fubar'd and it's only closing when properly cold - does that happen??
DrP
Sounds like its working. when stationry your engine will heat up till the stat opens then it will drop down a little then go up till the fan kicks in to cool it down again.
If its going up and down when on something like a motorway run then you may have another problem. if doesnt get hot when moving or staying hot then you got another problem.
hope this helps.
temp gauge fubbarred
Becoz is brokedificated.
Probably not much wrong, but check that the cooling fans aren't running all the time (or at high vehicle speed). They could be overcooling the engine. \Or that the thermostat is not stuck open (look at the o rings and installation of the thermostat housing - check that there is no way coolant can bypass the t/stat.
When did the problem first start? Was it when the weather got colder?
What car is it? Does the heater work OK?
Most cars will bias the coolant temp gauge around "normal", and the actual temp reading is not the number displayed on the gauge. you'll know if it's too hot, or too cold, but just because it says 80deg doesn't mean it is 80deg.
The other issue could be lack of coolant (air lock or something). If the coolant sensor is in air rather than coolant, it can read cooler than the engine actually is. Take out the coolant sensor, and make sure the coolant system is bled properly and try it all again.
Put thermostat in hot water. allow to cool naturally and use a thermometer to find out how cool it gets before it closes.
is it an oldish beemer ?
don't drive 300 miles away from home for the weekend as you'll end up showering in coolant 🙁