Temp guage fluctuating

Golf 1.8 MkIII 1986.

Since I've owned the car, the temp guage has risen to the centre line
as the car warms, stays there, bang-on, until the engine is swtiched
off and the car cools down.

Recently the guage is, on occasion, fluctuating slightly below the
centre (never above). I *think* this only happens when the cabin
heater dial is anywhere above off (cold), but not 100% sure.

The car is behaving normally otherwise, and the guage is still well
within the safe zone. I guess I should check it out though.

Does anybody have any suggestions as to why this is happening?

I dread that it may relate to a small quantity of stop-rust that was
added to the system.. (I know, I know...).. does that sound likely?

As always, TIA..







--
S i g n a l @ l i n e o n e . n e t

On Feb 28, 10:15 am, Signal <sig....DeleteThis@lineone.net> wrote:
> Golf 1.8 MkIII 1986.
>
> Since I've owned the car, the temp guage has risen to the centre line
> as the car warms, stays there, bang-on, until the engine is swtiched
> off and the car cools down.
>
> Recently the guage is, on occasion, fluctuating slightly below the
> centre (never above). I *think* this only happens when the cabin
> heater dial is anywhere above off (cold), but not 100% sure.
>
> The car is behaving normally otherwise, and the guage is still well
> within the safe zone. I guess I should check it out though.
>
> Does anybody have any suggestions as to why this is happening?
>
> I dread that it may relate to a small quantity of stop-rust that was
> added to the system.. (I know, I know...).. does that sound likely?
>
> As always, TIA..
>
> --
> S i g n a l @ l i n e o n e . n e t

Seems pretty normal to me. But if the fluctuation is new and the
swings wide, it may be that your thermostat is getting a bit long-of-
tooth, and is not closing all the way. As long as you are not going
over the top, your engine is safe. But if the temperature remains too
low, mileage will suffer.

With that in mind, and the recent thread on brake discs, one more
thing I do with "new" thermostats is drop them in hot water and make
sure they open when they should, and close when they should. This is
simply managed. Boil some water, pour it in a cup, drop in stat,
observe behavior. Add cold water, s-l-o-w-l-y, observe behavior. If
you have a candy thermometer to verify actual temperatures, even
better. Given how much of a PITA it is to flush and change coolant,
much less get to the stat in the first place, the proverbial ounce of
prevention is a good investment.

Peter Wieck
Wyncote, PA