I was on a long trip yesterday and was thinking over coolant temperature vs. mileage.

As some of you know, for no apparent reason, my mileage dropped from the traditional 20+ MPG recently to the 16-17 range. No CEL, no dirty plugs, no vacuum leaks.

However, I did notice that my temp gauge was indicating low compared to the reading I got with my laser heat gun. I swapped out the temp sender last weekend and the reading on the gauge returned to normal.

Previously on trips, my MPG was around 22 at a constant 80 MPH, and 20 MPG around town.

I had a 400 mile trip yesterday, same conditions, and pulled 25 MPG.

Since the Series II PCM apparently take it'* coolant temp reading from the gauge indicator as well, I have to wonder if a more accurate reading to the PCM resulted in the mileage increase.

Thoughts and opinions?

I know around here it can make a difference. As an example, gas mileage drops in the colder months, and I don't believe that it is all due to changing the gas formulation. It takes longer for the torque converter to go into lockup, the shifts are different, the idle is too, all due to a change in temperature. Will the change that you had be enough to make up the difference, especially in California temps., I don't know.

I would think so. Sounds like a logical explanation to me in addition to what Archon stated in his reply.