[s-cars] Local, intermittent overheating !???!?!

[Mark Strangways]

There just might be some air in the head, not likely though.
With a thermostatically controlled oil cooler it will get to 100 C or so and 
hold there if it can.

My best guess would be to get that thermostat out ASAP. Don't wait as you 
risk trashing your head, the aluminum one, not the French Canadian one.

Mark
----- Original Message ----- 
From: "Vincent Frégeac" <vfregeac at sympatico.ca>
To: "'audi s-cars list'" <s-car-list at audifans.com>
Sent: Wednesday, December 15, 2004 7:57 PM
Subject: [s-cars] Local, intermittent overheating !???!?!


Hi all,

Once again, my S6 is puzzling me. On my way to work, this morning, I noticed
the check light was on. I started to look at gauges to see if something was
really going wrong and, no, every needles are right where they should be.
Huh? Every needles? My car is one of those who shows 70 something as coolant
temp on the highway when the channel 51 displays a very stable 89-90C. This
time, the coolant temp on the dash is right on 90C. So I started to play
with the HVAC controller and channel 51 shows 112C! How! The next exit is
within reach. In less than 500m, the channel 51 reach 118C. Something really
goes wrong. So I took the first exit - to notice that channel 51 dropped to
111C during the exit ramp, probably because I'm coasting - park the car in
the gaz station parking lot and pop up the hood. Coolant everywhere, one
boiling inch remaining in the bottom of the coolant tank and electric fan
working. That's the first time I see it working and I notice it's out of
balance or rubbing somewhere as it's massively vibrating.

So, first step, let everything cool down, the engine and my head. Towing my
car is the last solution I want to think of as I'm in the middle of nowhere
and it will probably take two hours before I can have the required flat bed.
I'm 30 min. from home. If I drive 10 min, stop 10 min, I can probably reach
my trusty 90Q20V and be at work before the second meeting. So, I look for
water - no way to find the pink stuff in the middle of nowhere - feel the
coolant tank, wait until the channel 51 display a confortable 92 and start
the trip back to home to see how long it will take before I reach 105C, the
point where I've decided to stop and let the car cool down again. After 1min
of driving, the car have cooled down to 89C and stay there. 5km later, it's
still at 89C. So, as I'm not so far from work, I decided to take a chance.
And the channel 51 temp stayed at 89C, perfectly stable, when the dash
displayed the usual 70C. Some shit happened, I don't know what, buit now
it's gone. Good news.

So this evening, back to home. I took no chance and tuned the HVAC on
channel 51 from the beginning. Temp is climbing at it's usual pace,
everything seems OK and when I reach the highway, 5min later, the channel 51
just reached 87C. 10 seconds later, it reach the usual 89C while the dash is
still at 70C, everything is as usual. But it doesn't stop there, 90, 91,
92... Up to 99C where it seems to stabilize, probably because I'm going at a
slow 55mph to try to slow down the temperature raise. Looking at the dash,
the water temp is right in 90C, oil temp is just below the first thin mark
as usual. And I start the drive-cool down cycles until I arrive home. At one
point, while driving on the highway, the channel 51 suddenly fall from 104C
to 92C while the dash temp was falling from 90C to the usual 70C. Then, it
started to climb back to the 105-110C which was the maximum I allowed before
I stop the engine for cool down.

Now, in my mind, all that point to an intermitently stuck close Tstat,
especially the temp falling down from 104 to 92 while cruising on the
highway, but I've still some points I would need your usual wisdom:
- Why the dash temp is right on 90C and very stable when the channel 51 says
it's overheating and displays temperature from 92C to 118C.
- Why the oil temp stays perfectly stable, just below the first thin mark,
where it has always been - except during very spirited driving - when the
water temperature is everywhere between 89 and 118C.
- Why the dash temperature is stable (independant of speed) when the channel
51 fluctuate (overheating) and why the dash temperature fluctuate (depending
on speed) when the channel 51 is stable at 89C.

Besides, I've never heard of a Tstat stuck close, intermitently or not. Any
BTDT?




Vincent.

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