Hi, I am having troubles diagnosing this problem.
99 Audi A4 1.8T quattro.
The problem is as if the thermostat is stuck open.
Runs at full temp in summer with gauge in middle.
Runs cold in winter with gauge all the way at cold. No Heat! No Heater!
I have already changed thermostat with a new Audi dealer part. no fix.
Also changed temp sensor with upgraded sensor.

Is there a problem with the heater core? Blockage?
Is there a problem with a heat valve? Stuck in a bypass mode?

Please help with any ideas.
thanks,
chris.

 

If the heater core was blocked your engine would probably over heat. It sounds like an air pocket somewhere in the system. I had a similar problem with my Jetta. I changed the T-stat and it helped a bit. Try this....unscrew the coolant reservoir so that air can get out but not all the way off. I am sure you have heard the air come out when the cap is half open. Take the car for a ride with it half to 3/4 off for about 15-20 minutes. The turning and bumps may knock the air pocket loose. Then tighten the cap and see if it helps may have to do it a couple times.

Just to be sure....you didnt have oil in the coolant at all did you. Even a small trace of oil means you could have a bad head gasket and you could be getting a very small amount of combustion air in the cooling system. If that is the case then a head gasket is the only solution!

Hope that helps!

 

I know it is unlikely, but I have had new parts be "bad" and give me the same problem that the old ones did. My vote is for the bubble in the cooling system. Experienced it it my corvette as well as just low coolant level leading to no flow through the heater core. No other symptoms of cooling system woes other than no heat.

 

Thank you for responding.

When i replaced the Thermostat I refilled the coolant with a vacuum fill tool.
That tool insures all air is sucked out.
I drove the car and vacuumed again a day later.
No air was present. No additional coolant needed.
Since then it has been 6 months. I did not mess with it since it was summer.
Now that winter is approaching I want to resolve it.
The car has no oil in the coolant, has never needed topping off, and has never smelled like coolant so i don't think its a head gasket.

Please continue to bounce ideas with me
thanks
Chris

 

Just for kicks since it costs no money, do the trick that I mentioned about driving with the cap half off for a bit. Try that a couple times.

 

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thank you.

I think i will try to backflush the heater core next.

We will see what happens.

 

my audi a4 has no heat ...
but i can tell that the heater core is not plugged by touching the two houses coming out of it and they both are hot *** hell....gauges are working fine ....so do you think that there is some problem with the ducts? seems like something does not letting the air go through the heater core... and the buttons on the control deck are getting stuck some times...
t-stat wass replaced along with the t-belt and water pump.pls help

 

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well, i i'm suspecting a problem with the control deck, because it will show the temperature that i choose in this case on HI...and nothing happens, but i can feel the air flows perfect and the ac is in the good shape...so i will get cold air if i want to, bu I won't get the hot one...
I did not have chance to check for the cabin filter because i'm working out of town and i just got to open the thread...if you think that's the case can you tell me where that thing is located?
thanks