1.8T: Slowly oscillating temp gauge

2002 Passat GLS wagon, 1.8T, automatic.

Starting just this morning, the car warms up to the normal indicated
190F but from then on slowly drops to about 150F, slowly climbs back to
190F, and continues to do so, apparently unaffected by any external
conditions.

Until now, it warmed up to 190F and just stayed there.

Any suggestions?

--
Bert Hyman St. Paul, MN

Likely it is the thermostat.
Possibly the coolant temp sender.
Both have high failure rates.
Best of luck.

"Bert Hyman" > wrote in message
. ..
> 2002 Passat GLS wagon, 1.8T, automatic.
>
> Starting just this morning, the car warms up to the normal indicated
> 190F but from then on slowly drops to about 150F, slowly climbs back to
> 190F, and continues to do so, apparently unaffected by any external
> conditions.
>
> Until now, it warmed up to 190F and just stayed there.
>
> Any suggestions?
>
> --
> Bert Hyman St. Paul, MN

On 4/4/2011 2:07 PM, LM wrote:
> "Bert > wrote in message
> . ..
>> 2002 Passat GLS wagon, 1.8T, automatic.
>>
>> Starting just this morning, the car warms up to the normal indicated
>> 190F but from then on slowly drops to about 150F, slowly climbs back to
>> 190F, and continues to do so, apparently unaffected by any external
>> conditions.
>>
>> Until now, it warmed up to 190F and just stayed there.
>>
>> Any suggestions?
>>
> Likely it is the thermostat.
> Possibly the coolant temp sender.
> Both have high failure rates.
> Best of luck.
>
>

In addition to the above (personally I don't think it is the sensor, but
the thermostat was my first thought) check coolant level and make sure
there is no entrapped air in the system.

With the heater on, do you notice these temperature swings affecting the
heat from the heater?

--
I'm never going to grow up.

In PeterD > wrote:

> On 4/4/2011 2:07 PM, LM wrote:
>> "Bert > wrote in message
>> . ..
>>> 2002 Passat GLS wagon, 1.8T, automatic.
>>>
>>> Starting just this morning, the car warms up to the normal indicated
>>> 190F but from then on slowly drops to about 150F, slowly climbs back
>>> to 190F, and continues to do so, apparently unaffected by any
>>> external conditions.
>>>
>>> Until now, it warmed up to 190F and just stayed there.
>>>
>>> Any suggestions?
>>>
>> Likely it is the thermostat.
>> Possibly the coolant temp sender.
>> Both have high failure rates.
>> Best of luck.
>>
>>
>
> In addition to the above (personally I don't think it is the sensor,
> but the thermostat was my first thought) check coolant level and make
> sure there is no entrapped air in the system.
>
> With the heater on, do you notice these temperature swings affecting
> the heat from the heater?

Coolant level's OK and the heater behaved as well as ever though the
recent nasty winter. No noticeable fluctuations in heater output,
although the weather's finally starting to get to the point where the
heater's not on full all the time.

There's one thing I only just noticed, which wasn't obvious because of
the way I usually use the car.

If the car's been allowed to cool by being parked for a few hours or
more, or if it's only been stopped for a few minutes (like when buying
gas), the temperature seems to behave as always, rising to 190F and
staying there.

It's only when it's been stopped for an intermediate period, maybe
between a half-hour and an hour, that these temperature swings occur.

Since I don't usually do the sort of multi-stop errands that involve
these intermediate-length stops, this problem might have existed
un-noticed for quite some time.

Anyway, I'll look into replacing the thermostat when I have the time.

--
Bert Hyman St. Paul, MN

The thermostat is a fairly simple replacement. But, make sure the engine is
full cold before removing the plastic housing. Less likely to warp if all is
cold.

"Bert Hyman" > wrote in message
. ..
> In PeterD > wrote:
>
>> On 4/4/2011 2:07 PM, LM wrote:
>>> "Bert > wrote in message
>>> . ..
>>>> 2002 Passat GLS wagon, 1.8T, automatic.
>>>>
>>>> Starting just this morning, the car warms up to the normal indicated
>>>> 190F but from then on slowly drops to about 150F, slowly climbs back
>>>> to 190F, and continues to do so, apparently unaffected by any
>>>> external conditions.
>>>>
>>>> Until now, it warmed up to 190F and just stayed there.
>>>>
>>>> Any suggestions?
>>>>
>>> Likely it is the thermostat.
>>> Possibly the coolant temp sender.
>>> Both have high failure rates.
>>> Best of luck.
>>>
>>>
>>
>> In addition to the above (personally I don't think it is the sensor,
>> but the thermostat was my first thought) check coolant level and make
>> sure there is no entrapped air in the system.
>>
>> With the heater on, do you notice these temperature swings affecting
>> the heat from the heater?
>
> Coolant level's OK and the heater behaved as well as ever though the
> recent nasty winter. No noticeable fluctuations in heater output,
> although the weather's finally starting to get to the point where the
> heater's not on full all the time.
>
> There's one thing I only just noticed, which wasn't obvious because of
> the way I usually use the car.
>
> If the car's been allowed to cool by being parked for a few hours or
> more, or if it's only been stopped for a few minutes (like when buying
> gas), the temperature seems to behave as always, rising to 190F and
> staying there.
>
> It's only when it's been stopped for an intermediate period, maybe
> between a half-hour and an hour, that these temperature swings occur.
>
> Since I don't usually do the sort of multi-stop errands that involve
> these intermediate-length stops, this problem might have existed
> un-noticed for quite some time.
>
> Anyway, I'll look into replacing the thermostat when I have the time.
>
> --
> Bert Hyman St. Paul, MN