I was finally able to put some miles on it today. Did about 90 miles, mostly highway, with about 10 on a gravel road.

I'm pretty sure I still have some sort of cooling issue, but it kept the temperature within +/- 4* of the target temperature.

I have a 180* thermostat installed, and a target temperature of 203*. Outside temperature was in the mid 60s.

On the highway, it would creep up to 203, then fan would turn on, and by 206ish the fan was at full speed. It would pretty quickly drop to 203, and the fan would be back to idle by 201*. Wait a few more miles for the temp to creep up and it would cycle again.

On the gravel road the fan was at idle most of the time, staying right under 203*.

I'm going to tweak the algorithm again tonight, as I need to drive the same loop again tomorrow.

I think I'm really close to having an algorithm that should work well on most all cars. The problem I'm discovering is that my truck has an incredibly slow feedback time between when the fan speeds up and the temperatures respond. Andy's car is apparently the opposite; the fan comes on and the temps drop. I think I've found a way to adapt to either case automagically