Heater is blowing hot and cold

[Stuart1971]

Can anyone assist. I have a 97 Golf GTi 8v (AGG engine) and the heater blows hot and cold. Both pipes to the matrix are hot at bulk head and water temperature is normal. I have replaced the stat and water pump, cleaned out the matrix, checked the vent control flaps are opening. What's next. Don't fancy taking out dash to change matrix and garage will charge a fortune. I have spent that on her over the last year already. She's clean, tidy and original apart from this issue so want to resolve if I can or its time to part company. Shes clocked 110k and has history of the matrix being replaced in the past. Heater worked fine when I bought her 18 months ago. Appreciate any sensible suggestions to resolve this.

[tweed]

firstly you need to explains how its blowing hot and cold.

hot in one vent cold out another?

cold then then cold again?

if its the first then its the flaps. If its the latter then you've got a blockage or air in the water system

[Stuart1971]

Thanks.

The heater does not get very hot and takes an age to heat up. Heat does come out of all vents. Sometimes I get hot air when driving but it blows cold when idling or slowing down. My mechanic has checked for air blocks but does not believe this to be the issue. He has blown through the heater matrix and said there was little crud that came out and all appeared normal.

Any ideas?

[trog_nfs]

Thermostat would might be why it takes ages to warm up.

Whats the waterpump doing? Does the car temperature change at all?

[Stuart1971]

Not thermostat as already replaced. Water temp sits nicely on 90 degrees as it should and does not fluctuate. I have read that the golf matrix is susceptible to failure. I have been looking through Haynes and don't fancy taking dash out to replace it but may have no choice.

[tweed]

Well you've had some sh!t come out the matrix and your not getting hot air.


Enough said.

Firstly I would disconnect it and put a garden hose on the return pipe and try and flush it through for 10 mins.

If it still does it then I would replace it