Geza Polony <gezapolony@SBCGLOBAL.NET> writes:

> Here's my idea. When you're coasting downhill, you're using the
> engine as a brake. This means that above 1500 RPM, with the idle
> switch closed, the engine isn't getting any gas, as the ECU has shut
> the injectors down. If it isn't getting any gas, it also isn't
> producing any heat. The engine is functioning as a brake, but there
> isn't any combustion, and so, after a period of 10 minutes or so in
> freezing temperatures, the coolant loses temperature, and your gauge
> is way off the edge of the scale.

Makes sense.  Not only is there no combustion but you are flushing
cold outside air through the cylinders, which has a further cooling
effect.

> I tested this by going downhill, engine warm, and taking my foot off
> the gas to coast. I could see the gauge move colder before my
> eyes. Give it a little gas, and the engine warms up. This is kind of
> tricky from a driving standpoint, but it works.

Now, repeat the experiment with the clutch in, so the engine is
idling, not being overrun.  See if it stays warmer.

Allan