Originally Posted by Waste_Gate

This relates exactly to the lower mgp's I've been getting since winter started. I'm pretty sure my thermostat is partially stuck open. Last summer I only had to fill up about once every 4 weeks. At that time, I was reaching 85 degrees every time I was driving in the city. Since winter, I've been averaging about 75 degrees and have to fill up about every three weeks now.

I'm a constant gauge checker and last summer I always maintained 85 to 90 degree coolant temp on the interstate but this winter, I can only max at 85 and when I go from 80 mph in the interstate to 60 on back roads, it quickly drops to about 75 degrees, sometimes down to 70 (ambient temps of about 50).

I have a new 85 degree Behr thermostat and am about to install it with some zerex. I'll let ya'll know what effect this has on MPG. FWIW, I thought my temp gauge was inaccurate so I hit the thermostat housing with the IR gun and it was close to the gauge temp, then I ohm'd the temp sensor on the head and it matched the gauge so I know the gauge is reading correctly.

Willson,
85 300CD