REF: 1997 A4 2.8Q Std

I noticed once it got cold and I've needed to use my cars heater, that the system only blows hot air while the car is in motion AND the engine is engaged (so coasting in neutral, it gets cold). When I stop at stop lights or warm-up idle before I leave, it never blows warm/hot air, just 'natural'/cold air. Because the fan still works, I have to turn the system to manual control and turn the fan off because otherwise it just brings in the cold-cold Denver air until we are at a steady speed again...

Once I drive on the highway for about 15 minutes, it is up to its designated temperature and there are no issues...until I get off onto the side streets and have to stop at a stop light, in which case it cools off again.

1) I know that I have a slight coolant leak and have read that a leak MAY be a cause for this. True? It is not a major leak by any means, it is just there...

2) I also read that the cause could be the heater core being backed up. It would be with two hoses that can be found by removing the battery and they may be full of crud - they said to remove them, expecting to get coolant/crud everywhere, and blow them out with a compressor. True?

Any thoughts, explanations or confirmations of this would be great! Thanks!

 

sounds like my buddies VR6, it turned out to be a water pump going. as a temporary fix we put in some bars coolant leak stopper and so far its worked. chances are since oyu have a leak the system isnt pressurizing until theres load on the engine.

 

Sounds like you have air bubbles in your system.

 

It is very important to have your cooling system completely full. Also, check to make sure you have a thermostat installed and working properly.

 

I would look at t-stat as well.

 

Thanks guys! Since it there is not entirely a solid consensus or certain cause AND I don't have the proper space/weather, I will just let my mech look at it a little more in depth when I bring it in for some other work or just deal with it...

Also, how difficult is it to do an O2 Sensor replacement? I've never done that but I am increasing my experience around the engine. My friend said that I just need to diagnose which 'bank' (side) it is and the replacement shouldn't take too long? A little help if you can!

 

I drove home to Oregon over Christmas holiday and my heater stopped working. It happened to be the worst winter storm since 1968. I replaced the coolant temp sensor hoping that might fix it. Nope. $850 dollars later i had to replace the water pump and thermostat. They were original parts with 153,000 miles on them. The thermostat was stuck open not allowing the vehicle to properly warm up. The previous owner replaced the Tbelt but not anything else.

 

So did you have the same issue that I did and your heater only worked while the engine was engaged/in gear or did it just not work all together? Because now I am thinking that it may be my coolant temp sensor because the needle has been acting up a little bit lately, even with plenty of coolant...

For the first time ever, I had the coolant temp light come on last night about a mile before I got home while the needle was up near the "HOT!" zone. I got home, let it sit for a minute and then checked the coolant level. I forgot to post this before, and I don't know what it should be doing, but my coolant is never visible in the tank unless I open it to release pressure...does this seem like it could be an issue?

Basically, if I look at the tank without opening it, I have ZERO coolant...I then open it and it fills up and then it is usually about a quarter inch below the minimum level (because there is a leak somewhere...). All I know is that there is a reserve tank for the coolant somewhere and that coolant expands when it is hot...A LOT! Since the coolant is never visible until I remove the cap, does this mean that there is a pressure issue with releasing the coolant into the system? Because when I started the car up after a while last night and watched it, my coolanat level began to noticably disappear at about a 1/4 inch every minute...

HELP!!!