bleeding the heating system on a 1996 vauxhall astra

[mart123blue]

i have recently bought a 1996 astra 1.6 16v sport with the dohc engine. The heater blew warm a week ago but now only blows cold/luke warm which is murder in this weather.

I think I have an air lock in the heater matrix so i tried to bleed it yesterday by unscrewing the bleed screw on the thermostat manifold, and topping up the expansion tank.

Unfortunately the level in the expansion tank would not drop and only a little but regular drip came out by the bleed screw which I had removed fully. This was the case even with the engine running. I expected a steady stream of water once the air had escaped.

I think that the air is still trapped in the heater matrix and I want to undo the return hose to the engine to allow the air to escape. Unfortunately I have not been able to locate this hose.

Does anyone know where it is, or have any other suggestions that don't involve removing the heater matrix?

Thanks for your help.

[stanleyman]

The thermostat is usually the main problem so worth changing it anyway. The heater should clear itself of air if that is the problem. Check that all hoses are clear as air can be held back by a blocked vent pipe to the expansion tank. Heater matrixes can block up just like radiators and have a limited life of about ten years. You don't notice it until it gets cold.

[mart123blue]

Wouldn't the car be prone to overheating if the thermostat was duff. The actual cooling system works perfectly even in a 1/2 hour traffic jam during the week.

I will check the vent pipe to the expansion tank, it sounds like i will have to change the bl**dy heater matrix though.

Thanks for your help.

[stanleyman]

Thermostats usually stick open and over cool the engine.

[mart123blue]

The thermostat sticking open would seem right. Does it control the flow of water to the heater matrix though?

Thanks

[stanleyman]

No but the flow would increase when it is closed and nothing going through the rad.