Is it possible that water pump is "weak"? There is an interesting phenomenon in the coolant system which also affects the heating in the winter. When the the rev are up there is enough coolant flow and hence heat inside. When rev are down coolant circulation is poor and the air from the vents gradually becomes cooler. The temp gauge stays in the middle where it should be.Tbelt and water pumpwere done last year. Right now there is an universal yellow coolant which I will be flushed and the original blue G11 coolant will be put in.Any help will be appreciated


96 Audi A4 Q
120K

 

1.8T or 2.8?

 

2.8 12v

 

I would say the heater core is getting plugged up with the "universal" coolant thats in there, even if the water pump was weak the heat from the vents should still be warm if its going through the heater core, plus it would overheat.
What i would do is when you drain out the coolant take out the battery, and take off the two heater hoses going into the bulkhead and used compressed air in one of the hoses and blow out the heater core.
NOTE you might get drenched doing this.

 

Thanks auditech. That's what I think too - plugged heater core. Do you think I should do the thermostat as well? From what it seems to be there isn't a problem with it and it will involve more work, but...

 

You didn't change it when you did the Tbelt and water pump? Yeah i would change that as well cause they tend to not last longer than 80k.