[Jamo]

Steve...Southern's on the money in my book. Always harder to cool them down after they get hot.

I run a switch for the two pushers and the puller, and they get switched on once the car gets to about 75-80C on first warmup. They stay on unless I get on the freeway. I run a 160F thermostat and just a 13# cap.

In extremely hot (100-110F) Fresno summer days in stop and go traffic, the motor never gets above 85-90C.

I had a 92 Vette that I used to drive into XXXtreme heat (120F not unheard of...ask flipper) in Imperial Valley for work years ago. I put in a switch for the fans on that beast as well and never had a problem, though many Vette and F Body cars couldn't take it with their t-state controlled switches and bottom-sucking air flows. Learned this from the CHP which used Z-28s down there.

Glad you found the cause (the cap not sealing).

I also run very little coolant. Mostly Water Wetter and water. Learned that from autocrossing, where you run flat out for 1-2 minutes and then sit idling in the hot sun for 10 minutes waiting for your next run. Water is still the best cooling fluid...WW and a little coolant just add some essential lubricants.