2001 A8 / 4.2 - erratic coolant gauge?

[Gearhead62]

Greetings - looking for some coolant system assistance 2001 A8L w/ 4.2 (150K miles) has run at consistent normal temp on dash gauge, for as long as I can remember, but lately creeping up, to 1 tick, sometimes 2 ticks beyond normal, then down, back up, etc. I'm in Chicago which sees an fairly extreme range outdoor temps - has no effect - same behavior yearound. Lately, I'll start in any outside temp conditions and gauge hits normal and stays there for short driving period. After 10 minute driving, in city or highway, summer or cold, it climbs as high 2 ticks past norm, but usually runs at 1 tick above norm....The only time I can influence temp is when I downshift and send RPMs up - temp gauge then goes down to normal, until I shift back in auto / Drive, then back up between 1-2 ticks w/ normal driving My other observations: I don't think stat has ever been replaced? No coolant leaking I get normal heat in winter I have NOT checked relays yet If parked and idling, temp hangs at normal or slightly hotter Aux fan kicks on only with AC ("econ switch off") - normal? Any logic from this or what should I check? Thanks - GH62

[silverd2]

Originally Posted by Gearhead62

Greetings - looking for some coolant system assistance

2001 A8L w/ 4.2 (150K miles) has run at consistent normal temp on dash gauge, for as long as I can remember, but lately creeping up, to 1 tick, sometimes 2 ticks beyond normal, then down, back up, etc.

I'm in Chicago which sees an fairly extreme range outdoor temps - has no effect - same behavior yearound. Lately, I'll start in any outside temp conditions and gauge hits normal and stays there for short driving period. After 10 minute driving, in city or highway, summer or cold, it climbs as high 2 ticks past norm, but usually runs at 1 tick above norm....The only time I can influence temp is when I downshift and send RPMs up - temp gauge then goes down to normal, until I shift back in auto / Drive, then back up between 1-2 ticks w/ normal driving

My other observations:

• I don't think stat has ever been replaced?
• No coolant leaking
• I get normal heat in winter
• I have NOT checked relays yet
• If parked and idling, temp hangs at normal or slightly hotter
• Aux fan kicks on only with AC ("econ switch off") - normal?

Any logic from this or what should I check?
Thanks - GH62

First, it's been established that the temp gauges in our cars are actually idiot lights with needles. The instrument processor "filters" the signal to the gauge to read dead steady normal from 81-100C, making us believe that it's actually always at 90C (what that mark is "supposed" to mean.

So, if the gauge climbs above the "normal" mark, the temp is actually well above normal range...2 marks up is seriously high.

Running high rpms will cool down a motor with a failed thermostat...Mine is on it's 3rd, installed at 100K miles...very prone to failure in these cars for some reason. High rpms seems to force coolant through the bleeder hole in a thermostat stuck closed. Running max heat and max fan will also cool down the coolant.

I'm guessing a failed thermostat over a coolant temp sensor...judging by your mention of cooling things down with high rpms...a failed coolant temp sensor would not respond to that, but a stuck closed thermostat always will.

You can read the true temp of your coolant with a climate control trick in the link below...it's code #102...easy to do and a useful tool built in that most D2 owners don't ever know is there.

Check it out >>>

http://forums.audiworld.com/showthre...t=secret+codes

[Gearhead62]

Silver

Thnaks for info....Any estimate on what I am looking at ($$) for stat replacement?

Also, shouldn't that Aux fan kick on periodically? It only runs when econ switch is off

Thnaks......GH

[sonata54]

Originally Posted by Gearhead62

Silver

Thnaks for info....Any estimate on what I am looking at ($$) for stat replacement?

Also, shouldn't that Aux fan kick on periodically? It only runs when econ switch is off

Thnaks......GH

From what i've noticed, my aux fan turns on everytime i turn on the a/c or heat.

as far as the price goes, I don't think its cheap. The thermostat is in the front of the engine(I think behind the timing belt), which means you will have to have the timing belt removed using special tools and what not to get it off/on.

[sonata54]

Also, the thermostat itself should only be 20$-30$(with the O-ring)

[silverd2]

My local dealer quotes people about $500 for the thermostat change...it's buried deep. Some "skilled" home mechanics have slightly shortened the procedure, but not by much...still very involved, requiring a good deal of knowledge.

The aux fan always runs with climate control in "auto" regardless of temp. The fan kicking on by itself (due to heat) is controlled by a switch at bottom right of radiator...coolant IN radiator must be well over normal range temp to kick it on.

[Gearhead62]

Thaks all - good info

OK - seems a stat issue - to be replaced

As for the elec aux fan - seems it should kick on, based on temp sensor, only in Auto mode?

I don't ever see it engaging when climate control is in "econ on" mode - is that a faulty sensor or normal?

Im in econ mode all year except summer

[silverd2]

Originally Posted by Gearhead62

Thaks all - good info

OK - seems a stat issue - to be replaced

As for the elec aux fan - seems it should kick on, based on temp sensor, only in Auto mode?

I don't ever see it engaging when climate control is in "econ on" mode - is that a faulty sensor or normal?

Im in econ mode all year except summer

Fan always runs in auto, but not eco...normal.

It's possible for the motor to overheat, with radiator water remaining cooler...a closed thermostat is preventing low temp coolant from getting into the block and unloading overheated coolant into the radiator.
The coolant temp sensor is on the back of the motor...and the thermal switch for the fan is mounted on (and reading coolant in) the radiator.

[Gearhead62]

Silver

Earlier in the thread you said temp needle showing 2 ticks up is very high. When I say 2 ticks, I mean needle is at 12 O'clock....Doesn't go past that. Keeping in mind your comments about the needle is not a good indicator, just curious if that needle reading is very hot. I will also try the codes you suggested - good stuff

Thnx

[silverd2]

Originally Posted by Gearhead62

Silver

Earlier in the thread you said temp needle showing 2 ticks up is very high. When I say 2 ticks, I mean needle is at 12 O'clock....Doesn't go past that. Keeping in mind your comments about the needle is not a good indicator, just curious if that needle reading is very hot. I will also try the codes you suggested - good stuff

Thnx

That's still above normal, unless you were standing still and idling for a long time in very hot weather.

The "secret codes" are REALLY easy to use...I do constantly.
With climate control on, simply press the recirc and upper vent button drivers side at the same time (2 fingers at same time)..then use the drivers side temp button(s) to scroll to "102". The passengers side temp window will show the true temp (Celsius) constantly, so long as the temp sensor is working properly. You'll notice that the temp gauge will hold dead steady at normal mark (90C) while temp is actually 81-100C, and will not increase until true temp goes over 100C. Normal temp should be 87-93 in most cases...esp with car in motion at any outside temp.