F-head thermostat issues

Anyone else encounter this:

When I bought my 62 it would never warm up. I pulled the thermostat out, and low and behold, it was bad. It was also the original which is pretty cool looking. Like a butterfly valve. I saved it because it is just 'cool'.

Anyway, I installed a new 180 degree thermostat and noticed something with the temp gauge. As the engine warms up, it warms up past 180 degrees. You can watch it warm up hotter and hotter and see when the thermostat opens up, the temp drops right to 180 and holds 180 degrees constantly, no problem.

If I start it up and immediately floor it up the long hill out of my neighborhood, my coolant temp gets REAL high before the thermostat opens up. Once it opens up that first initial time, it regulates the temp to 180 solid as a rock. So the thermostat is good, but looking at the design of the F-head, the thermostat is forward of the rest of the motor a decent amount. It is just taking forever for the heat to hit the thermostat so it starts flowing coolant.

So I figured I'd drill a small hole in the edge of the thermostat to get a little bit of coolant flowing so the thermostat doesn't have to wait for heat soak to open the first time.

I drilled an 1/8" hole in the lip of the thermostat. Well, it works great. A little too great. Now the jeep won't stay at 180 degrees when idling or going downhill (i.e. low/no load situations). So 1/8" is too big. It's amazing that a 1/8" hole will flow enough coolant to cool down this motor so much.

I looked at the original thermostat again, and guess what I found? A 1/16" hole in the thermostat to flow just a small amount of coolant.

So I picked up another thermostat and drilled a 1/16" hole in the lip of it. Now the jeep warms up fairly quick, gets to 180 degrees and holds that temperature rock solid.

Maybe it's just this brand of thermostat I'm using that seals up too well when closed? It appears just a little bit of coolant flow to make the thermostat aware of coolant temp really works well.

Hope this helps anyone that has also experienced this trend.

Anyone else experience this with their F-head motor?

 

I am a firm believer in a tiny hole in the thermostat but the reason I like it is so air doesn't get trapped in the system.

 

what Glenn said
just means an "active" thermostat is doing it's job.
some are more "active" than others