Quote Originally Posted by 1bigdually View Post
First, the facts
1970 Nova
th350 w/shift kit
95 2 blot main short block
world s/r torker heads
isky 270 cam
edelbrock performer intake
pete jackson gear drive
holley 850
manley guides and valves
3 row aluminum radiator w/ 16" electric fan
8 qt moroso oil pan
moroso high volume/ high pressure oil pump
15" ralley wheels

After I put this motor together, i had an oil pan leak. I had used the one piece seal from felpro. I lifted the motor up enough to get the pan off (along with removing the steering linkage). I removed and replaced the seal with another one piece from felpro. I finished after dark so I couldn't read the temp guage. On the way home, there was a good sized BOOM along with a lot of smoke. The motor shut off. I finally got it restarted (in the dark) and got to the nearest gas station. I saw the distributor was not completely down. I assumed that was the problem, fixed it, and got home. I usually run around 190 degrees, but it started running hot. My aluminum fan had quite a few holes over the years, which I "fixed" with bars leak. I changed out the old two core for a new 3 core and larger fan. I also changed to a 165 thermostat.

Prior to the changing of the oil pan, I had no overheating problems. After I changed out the radiator, it was still overheating, only when picking up speed or under a load. I could stop and let it idle and it would cool right down. I susected a blown head gasket. I had it tested and they found C02 in the overflow tank and said it was a blown head gasket. I spent the last two days changing out the head gaskets. I filled up the fluids and went for a test drive. Nothing changed. I get up to 250 degrees rather quickly when I am going over 45 mph or when I climb a hill. As soon as the load is taken away, it cools back down.

Any Ideas?
A blown head gasket can be tested for without chargning into swapping gaskets but you are past that point...

Check your oil and coolant, condition and levels. Oil will turn a milky green if there is antifreeze in it and antifreeze will get dark and slimier with engine oil mixed in. If your coolant level is too low you can experience flash heating issues, but your cooling system may be "saving" you

Tell us about your electric cooling fan, how is it controlled?
Do you have a water temp gauge or just an idiot light and where is the sending unit installed?

Regarding your thermostat, 165 is quite low... I would think 185-195 would be better...

Not sure about the big boom you mention, need more details to "guess" but usually there are consequences of such noises. Have you done a compression test on that engine since the boom?