Fine-tuning engine temp using the heater control valve.

[ThermionicScott]

This may fall into the "well, duh!" category, but I thought I'd pass it along anyway:

It's common knowledge that you can take the edge off an overheating engine by cranking up the heater. While on the way home from running errands today, I noticed my FWT reached 204°F. Not wanting to trigger the radiator fan(s) but also not needing to heat my person, I tried just moving the temperature slider to the "hot" end of the scale without turning on the heater fan. FWT went back down to 196 or so, aided by a short (engine-on) coast down a mild hill. Neat. Just for fun, I moved the slider back to the halfway point, and the temp rose back up to 200 or so, and I was able to keep the temp right around 200 the rest of the way home.

When I got back home, I did a little more research and learned that the slider control adjusts how much coolant is flowing through the heater core. When the slider is all the way on the "cold" end, no (or almost no) coolant is making the trip through the heater core, and on the "hot" end, you get full flow through there. So without turning on any energy-sucking devices, I was able to give the hot coolant a little more opportunity to shed heat.

Just the thing to keep your engine in the sweet spot without activating the radiator fan, then. And also a reminder why, even if you don't have the cabin air fan engaged, it's good to have your temperature control all the way on the "cold" end when starting and warming up your car.

[oil pan 4]

It depends on the vehicle. Most use a valve. Some run full flow though the heater core and block air flow. Those are the ones where the heat never seems to fully turn off. Old GM vehicles mainly.