Heater pipe thread pitch?

jagplates

Can anyone confirm whether or not the threaded hole in the cylinder head of a 212 splasher engine is 5/8 18 thread?  I am installing an electric fan and I want to use the heater pipe hole, since I don't have a heater & the hole is just capped.

Frankvintagefullflowcom

It's actually a 3/8 NPT thread which shares the same thread pitch with the 5/8-18 machine screw thread. At a glance, they may appear identical.....but they aren't.

Frank

jagplates

Thank you.  It looks like no one mass produces a fan switch for 180 degrees anymore.  Aftermarket choices from Hayden and Derale received bad ratings for rapid failure and coming on at too high a temperature. I guess the best choice is a more expensive one from Ron Francis Wiring (through Summit Racing. Part # AR-33  comes on at 176 degrees. 3/8 NPT threads. Ron Francis products are said to be high quality. Pricey at $45, but what're ya gonna do.