99 A6 quattro 4.2

well at first I was convinced the thermo was gone and was preparing myself to rip it all apart. not a daily driver so it has sat for a month since it's last boil over. went to move it today and the temp shot up well over half during a 10 minute drive around the hood. turned on the AC and the electric fan came on and then stayed on after I turned the AC off resulting in a cool-off almost back to half. Maybe the thermo worked for a moment or two?
Also I have read several threads on the clutch fan. supposidly you can not spin the fan once the engine is hot and turned off? I can and if I take a roll of paper towels with the engine running and apply presure to the fan (when engine temp high) it stops. is that normal? or is my fan toast. I'd rather start with that if that's the case. also now I have cold on one side, temp turned to lowest and AC fan on, and heat on the other even though temp is set to low. WTF? scrolling back and forth with the temp does nothing!
Thanks for any input!

 

make sure your full of coolant.

Pull your thermostat out and see if it cools with out it if it does replace it if not I would look at the water pump or a restricted radiator.

Even if your fan clutch was failing it sounds like your overheating a lot faster than that. Sounds like a thermostat or water pump or low coolant or blockage but something keeping your coolant from circulating would make it overheat that fast.

 

hey I'd love to just pull out the thermo like I have on many a car in five minutes but according to everything I've read the thermo is burried in the engine. I've read quotes of up to 2k to get at it and replace everything along the way. just did my expo in a few minutes as it was boiling over so I knew it was stuck closed. the goofy thing is i took apart the "t" just below the coolant resivior and hosed forced water through each side of the "t". one side goes through the radiater and the other back into the engine. I disconnected the sensor that plugs the radiator hose (lower pass side) and water came out of it in a rush from both "t's" . If the thermo was stuck closed water should have backed up from the engine side right? but then again it should be closed if cooled? if it was stuck open the engine would not overheat???

 

I'd start by replacing that fan clutch. Your analysis shows that it is not working properly, so you might as well get it fixed first to see if that solves the problem. As you pointed out, the t-stat is not an easy replacement so you want to do that last. Question, when the engine first goes "hot", are the upper and lower radiator hoses also "hot"? If so, it isn't the t-stat. If only the upper is hot, then it is the radiator. If neither are hot, then it is either the t-stat or water pump. It won't matter which as you would replace both at the same time.

Bob

 

hey bob thanks for the reply. yes the hoses are scorching hot all around the t and into the radiater. as for the lower hose are you refering to the hose (above mentioned) that the lower sensor is in that connects to the lower left of the radiater (looking from front to back) ? have you used any other coolant than the g-12 ? I keep reading conflicting info here on what is ok to use. some say "good with any coolant" is fine to use. others say only g-12. I'll order a new upper temp sensor ($20) and fan clutch and go from there.
any idea what could be going if one side is hot and the other cool as I meant to say in the first post heading?

 

Let me see if I understand this:

1 - Overheats under conditions with no/low air flow through the radiator.
2 - Cools down when A/C is turned on. (Electric fan blowing on the radiator.)
3 - All hoses to/from radiator heat up. (Indicates coolant flow.)

I would agree with Bob. Fan Clutch.

The Fan clutch should work like the one on my old motorhome. There is a viscus coupling (like a torque converter) between the driven shaft and fan. The fluid in the coupling is controlled by a thermostat type device (bi-metal spring) mounted on the center/front of the coupling. When the air around the bi-metal spring gets hot, it opens a valve allowing the fluid to be pumped and engaging the fan. On my motorhome is engages with a distinct "roar" sound. I haven't heard this sound from my Audi so I expect the coupling "slips" a little as it engages.

As the fluid is held in place by centrifugal force, it is hard to check the fan when it is not turning. On the motorhome, it shows some resistance to turning when off and cool. When started it should engage for a short time as the fluid gets distributed, then disengage until it gets hot.

 

Only use G-12 pink (which is the old style) or G-12+ purple (which is the updated version of the pink).

You just can't use anything in an aluminum block and if you mix the two it will become corrosive. that sure as hell won't save you money.

Sure there are guys that will tell you the German engineers who design the cars everyone wants have no idea what there talking about, But come on...

I buy mine concentrate from www.blauparts.com but use water till you get this resolved for now. No sense in wasting it on the driveway.

I agree with Bob, check your hoses, and you have to replace the clutch anyway. Sorry I have only done the thermostat on my 3.0 not 4.2 yet, it does look burried but believe me not 2K worth of burried however if you are going in for that do the whole mess and get it all over with. I hear the 4.2 is easier than my 3.0 but won't be able to officially say that till this winter when I do that one.

My 4.2 has electric fans, Yours doesn't?

If you are however experiencing better cooling at high speeds and you return hoses are too hot to touch then I would say it's a fan issue. Problem is the water pump and Thermostat should be ready to fail at 100K. So any way you look at it you may need to do it all.