Since we are talking about temperatures again, I thought I would post the interesting results of the SDL in cooler weather.

When warmer, the temperature gauge would function like a boost gauge. If I used boost for 30 seconds or more, the gauge would climb right up from 90 or so and head toward 100. Would never go above 100, with the one exception of a five mile upgrade in West Virginia when it made it to 105 under full boost and 80 degree ambient.

So, now, when colder, it behaves in a very similar fashion, only a bit cooler. It typically sits at 87 or so, under limited or no boost. Under heavy boost, it does its usual climb up to about 95-96 or so. Remove the boost and it returns to its typical 87-89 setting in the colder weather.

I'm now convinced that this behavior is normal for this engine and there is a differential between the thermostat and the guage. The function of the thermostat must allow slightly higher temperatures under heavy loads and that is what the guage is showing. I conclude this because the cooling system has ample capacity to keep the engine precisely at 90 degrees if the thermostat would allow it.

The only other possibility is that the thermostat is defective and is not able to precisely control the outlet temperature anymore.

Thoughts?