I was having trouble with my '72 Chevy C-10 six-250: while driving from a cold start, the temp gauge would go way over to the hot mark (within one mile of driving), then suddenly the 'stat would open and the gauge would drop back to normal.
Needless to say, this got my attention. I replaced the 'stat several times, with the same result each time.
Finally, a friend suggested that there was an air pocket, so I drilled a 1/8" bypass hole in the 'stat flange, figuring that would allow enough circulation to bleed any air bubbles and release any trapped steam.
So far it's worked great, although that little 1/8" hole adds a surprising amount of time to how long it takes the engine to reach "operating temp". But, it's a nice gradual rise
, no nasty spikes to hot accompanied by the unmistakable aroma of anti-freeze!
