Strange coolant temp guage movement - 98 A4 V6

Could be the Tstat or sensor but it could also be low coolant and a bubble in
the system.

Ed H. wrote:
> This just started happening. On cold mornings the engine takes a while
> to warm up - say 4-5 minutes after driving. Used to be much quicker.
>
> Now the really odd thing is the water temp gauge (no degrees, just
> marks) used to be just to the left (cool side) of top dead center when
> warm. Now, it will go straight up, then in a few minutes, actually
> fall to almost where the "C" is and then move up again. Would a bad
> thermostat cause the needle to swing wildly like this? I originally
> thought it was the thermostat until the gauge did this strange
> maneuver and now I am wondering if is the sensor out of whack.
>
> The oil temp seems to be fine.
>
> 98 Audi A4 V6, 2.8l Quattro, 5spd. US model.

It's probably the sensor. I had to have mine replaced on the same car -
around $200 at the dealer IIRC. Thermostats usually fail by sticking in some
position so the behavior you describe is unlikely. .

Ian writes:

>Thermostats usually fail by sticking in some
>position so the behavior you describe is unlikely. .

I agree. But, on the chance it *is* a thermostat, while you down and in there,
ya might as well replace the timing belt and the water pump.

Dave
RS6

"Dave LaCourse" > wrote in message
...
> Ian writes:
>
> >Thermostats usually fail by sticking in some
> >position so the behavior you describe is unlikely. .
>
> I agree. But, on the chance it *is* a thermostat, while you down and in
there,
> ya might as well replace the timing belt and the water pump.
>
> Dave
> RS6
Yes, definitely, if you're replacing the thermostat, the TB and WP should
also be considered unless they've been recently replaced. I still think the
OP will discover it's the sensor.

The easiest thing to replace is the temp sensor. I just had an issue
with my 2001 A8 where my needle used to run about 1/4 on the gauge and
then started going to half, and eventually 3/4. The car had plenty of
heat and although it never overheated, it would run high enough so the
electric fan would click in on high speed. It turned out to be a
thermostat. If it were a Chevy, it would have been about 4 bucks and a
15 minute job but seeing how it's an Audi, it was $2026 and 2 days. It
was about time to do a timing belt so that service, along with a water
pump, pulleys, thermostat, tensioner, serpentine belt, and antifreeze
were all replaced at once. Just the thermostat would have been about
$1000 due to the labor involved in getting to the $14 part.

If your car has around 80k on it and the timing belt hasn't been
serviced, you should get it done. I had a 98 A6 that I did the timing
belt on and it wasn't that difficult. You have to buy a couple of
special tools though. One tool locks the crankshaft at the top dead
center position for the number one cylinder and the other holds the cams
in place so you can keep them aligned with the crank shaft. I think they
are about $140 for both. The parts you will need will cost you about
$200-$300 Wich will include thermostat and gasket, water pump and
gasket, timing belt, crankshaft seal, serpentine belt, tensioner pulley,
and idler pully.

Good luck! Dennis

Ed H. wrote:
> This just started happening. On cold mornings the engine takes a while
> to warm up - say 4-5 minutes after driving. Used to be much quicker.
>
> Now the really odd thing is the water temp gauge (no degrees, just
> marks) used to be just to the left (cool side) of top dead center when
> warm. Now, it will go straight up, then in a few minutes, actually
> fall to almost where the "C" is and then move up again. Would a bad
> thermostat cause the needle to swing wildly like this? I originally
> thought it was the thermostat until the gauge did this strange
> maneuver and now I am wondering if is the sensor out of whack.
>
> The oil temp seems to be fine.
>
> 98 Audi A4 V6, 2.8l Quattro, 5spd. US model.

In message >
Ed H. > wrote:

> Well, I hope it is the sensor. I described the behavior to them Friday
> and they agreed with the general opinion. I had the timing belt and
> timing belt tensioner replaced in December.

You /did/ have the water pump and thermostat changed at the same time,
didn't you?

> I'd hate to go through much of that expense again if it is the
> thermostat. :-|

Indeed.

--
Peter Bell (Note Spamtrap - To reply, replace 'invalid' with 'bellfamily')

On Sun, 30 Jan 2005 17:59:10 -0600, Ed H. >
wrote:

>Well, I hope it is the sensor. I described the behavior to them Friday
>and they agreed with the general opinion. I had the timing belt and
>timing belt tensioner replaced in December. I'd hate to go through
>much of that expense again if it is the thermostat. :-|

Funny you mention this because my own A4, identical model and vintage
as yours, does/did the same thing after getting a whole new TB/TB
tensioner, and water pump at 69k miles. Before this work was done,
the coolant gauge would stay rock solid right on the middle hash mark,
and afterward it would wander up almost to the next hash mark and back
down and back again. This wandering behavior has stopped for the time
being (our temps are freezing right now, with lots of snow and ice on
the ground, reaffirming the perfection of the A4 for my driving
needs). The gauge never passes that next hash mark except when the
engine is turned off and the car is hot; once I get the engine started
and the radiator cooling, the gauge moves back down again. I've lived
with this now for almost $15k miles and just keep my eye on it for the
reason you state: I really don't want to fork over the labor $$ to
change out the sensor/thermostat.