Best possible mileage?

Go Duggie go, you're on the right track!
Get yourself an IR gun and verify your thoughts on the heat thing.

Thanks for the guidance! When I did the head, mains, and crank seal, I popped the freeze plugs and flushed out sand from the water jacket. Replace the radiator too. The old radiator leaked everywhere. When the 180 deg. thermostat opened, the engine stayed at 180. I used the wife's meat thermometer in the radiator neck to confirm the stat now opens at 195. The needle didn't move on the dash for yesterday's trip but its 40 deg F outside right now.

@YY1, I love reading your stuff man! :thankyou: Without this forum, there is no way this car would look or run as good as it does. A 318 'aint happening man. I've caught the slant sickness. There is something nostalgic, and just plain fun about tinkering on this 6. That warm glow that comes on while driving this antique out of a clover leaf onto the freeway onramp is partly due to how this little motor purrs. :rolleyes: