Heater / coolant problem..............thermostat???

[ianess]

Vauxhall Astra [2000W reg] with heater that only blows hot when going uphill, then cools down rapidly. No sign of leakage but topped up expansion tank [ needed 3 pints]. Also temp gauge only works intermittently going fom low to normal....never high.
Any advice most welcome.

[Pies]

Possibly a knackered water pump

[stanleyman]

Does sound like the thermostat, although topping up has possibly been neglected over the summer, loss of coolant could also be the pump or head gasket leaking, this could give the same problem. Change the thermostat first and see if it settles down. Look for telltale water and rust marks from under the pump drain hole to see if the pump is leaking.

[Andy Boz]

Ensure when you top it up there is no airlock in the system, there may be a cooling system vent somewhere. I would change tthe stat anyway.

When you are going up hill, the available coolant is going by gravity to the rear of the engine, and hence into the heater matrix. You say temp gauge intermittant, thats a sensor that should be immersed in coolant, but it will work in steam, at the top of the engine. Both of these symptoms point to water level problem.

[fountain]

I have exactly the same problem on my car (escort) and am convinced it is a failed thermostat. The stat fails open so coolant is always directed thru the radiator. So unless you put the engine under heavy load (ie uphill) or remain stationary, it never really warms up properly. This also explains the gauge problem. Try leaving the car to idle for a while without moving and see if the gauge shows normal and you are able to get hot air through the blowers. If yes it has got to be the stat.

[Adampy]

I have the same problem with my golf CL. I have had it at the mechanics and the thought it was the stat, they replaced it but no difference. Then they though it was the impellor on the water pump? still not luck, then they sais the heater matrix was blocked is that possible. They said they would have to take the whole dashboard out to fix it? I do have to top up the expansion tank about every third day but cant find any leaks when I look under the car? I was about to sell the car as it was too expensive to fix, but if you might know something that would be a great help!

[Adampy]

Oh yes forgot to add, When the heater did work the temp gauge read really low (about 50 degress) while driving. After been in slow traffic for a while about ten mins it reached 110!! But it never boild over and the radiator fan was on. But since the heater stopped working, the guage reads the same while normal driving but as soon as you stop, like in traffic, the guage starts to rise immediately, And FAST! about 2 minutes to reach 110. I have offerd to sell the car to the mechanic, but I am worried I am been ripped off (It is a AA recognised garage if that means anything) Thanks again.