Overheating while car is stopped
 

So after I replaced the valve cover gaskets I went for a drive to make sure that there was no oil leaks, good news, no leaking oil. However, after my drive we went through a drive through, while stopped the dash light came on and the car started to overheat. The primary fan is running, the small higher one didn't come on. I checked my fluids after it cooled down, the levels are right where they should be. According to maintenance records from the dealer the timing belt was done about 15K ago with the water pump and the thermostat. Could I have knocked a connection loose for the axillary fan? or disconnected a high temperature switch? Once I got her back on the road she was fine, only standing did she overheat. Any advice would be appreciated.

I've been reading up online that most of the time it is faulty thermostats that cause this problem but it is quite a job to replace it. I'd never seen a vehicle with so many componets that needed to be removed to get to a thermostat. It talks about having to lock the cams in place and removing the primary fan and fan clutch....maybe it's time to call up my mechanic..

If this is on your 98 A8 (as I recall?) and it IS the thermostat, you're in luck. It is the ONLY thing that's easier on the 32V than on the 40V engine. It's actually accessible without doing any of that stuff, unlike the 40V which requires almost the full timing belt job to change (I've done it).

Look at this (1st post) :

Thermostat on 32v engines - super simple - AudiWorld Forums

Does the electric fan run at all? ..or just at low speed?

That fan should run continuously if the AC is on...cold or hot motor.

I do have a 1998 A8, I thought it was a 40 valve vice the 32, I hope so. The fan doesn't turn on when the A/C is on, the A/C is kinda funny too, it will work well most of the time but it seems to warm up for a few minutes and then get cold again. The driver's side is never as cold as the passenger side. The engine fan is always on but the axillary fan never turns on. Could it be the relay? a sensor?

First, that fan is absolutely essential to proper AC operation...one of it's main jobs is to cool the refrigerant for the AC...that's why it HAS to run all the time the AC is on...even with cool engine. If it is not running the car will intermittently disable the AC after the engine warms up (esp at hot idle). Warmer air on the driver's side is also a classic indication (in A8's) of low freon level, but that would not disable the fan...that's a separate issue.

The fan also has 3 speeds...upper 2 generally are to help with regular engine cooling. Sounds like the fan is likely the main (only) thing leading to your overheating, since you stated it only happens at idle and cools down while driving...bad thermostat would continue to overheat at any speed...unless you have multiple problems, but the fan has to be addressed 1st.

The fan gets it's power from a 60amp fuse (I believe uppermost fuse in your main fuse panel..it is in later models). The fan is also controlled by a 3 phase control unit (series resister) under the driver's headlight...flat metal unit. There are 3 different relays for the 3 different speeds that send signals to the control unit, also thermal switches, AC etc.
But since the fan is not running at all, I'd start with the fuse, then wiring to the control unit (you may have knocked something loose), then wiring to the fan itself....I don't think any single relay or switch would completely disable the fan.

I checked my fuse box and found that the large fuse had gone out, replaced it, problem solved. I had checked the fuses already but not that large one.

Glad you got that fixed...but VERY unusual to blow that big fuse.

Maybe accidentally shorted the resistor board under the hood or something(?)

running hot in slow traffic
 

Hello all, I just registered but I've followed this forum for years.

I've had cooling issues since July of this year (I've had the my '00 A8 - 40V engine - for 7 years, 135k on the clock, never had it). The car has been running hot in slow traffic. I do not hear the aux fan running when the engine temperature increases to 100°C and after a hot shutdown. No coolant loss and no serious overheating since I keep an eye on the cluster and pull over when my T-gauge comes close to the second thick mark. Infra-red thermometer confirms the coolant temperature I see on the display.

Aux fan is running properly with A/C turned on, but I don't see/hear it coming if the A/C is turned off.
The 2-speed thermal switch is operational - I had removed and tested per silverd2's instructions. Jumping the wires turns the low and the high speed. I take it my relays and 60A fuse are OK, the fan too.

The fan clutch was replaced last week, although this probably wasn't necessary. Serpetine belt appears fine.

I think I can rule out thermostat and water pump as high speed drive is normal, my gauge shows 90°C steady and the temperature goes up only in slow traffic. Appears to be sensitive to ambient temperature too.

Please help, I am at lost.
Thanks,
Steve

No specific theory right off hand...but if you weren't already aware of it, the temp gauge in our cars is basically an idiot light...a little white lie from Audi. I and others have discovered that the gauge is damped to read 90 (1st thick mark) whenever the temp is anywhere within acceptable temp operating range. You can prove this to yourself, plus get a true temp reading (may be much higher than you think?). I found, with the following method that the normal gauge, even though being fed the correct signal, will reach the "90" mark at about 81 C and stay there steady till 99C and then start moving up proportionally as temp goes 100C and up.

The link below will show you how to activate "secret codes" with your climate control buttons. As you'll see, code 102 is the signal being fed to your gauge (I've confirmed this though the wiring from the double coolant temp sensor (rear of motor..Audi G2 & G62)...the other sensor feeds the ECM for fuel/ignition adjustments. When set to 102 on the left CC display, the right display will show the coolant temp being sent to the gauge in Celsius.

http://forums.audiworld.com/showthre...odes+revisited