Temperature spike on rebuilt 235 on initial warm up

[blackbeard]

I have a question for the experts. I have a newly rebuilt 235 in my 1959 Chevrolet truck. I have only put a couple hundred miles on it since the rebuild so I am still breaking it in. It is running great. The one issue I am seeing is when I initially fire it up and start driving down the road the temperature gauge will gradually rise until it pegs on hot. This only last for a very short time maybe a couple minutes then the temperature goes back down to normal and stays in the normal range for the duration of the drive. This only happens when I initially start the truck when the engine is cold and last for a very short period then the temperature stays in the normal range. I have removed the radiator cap and let it warm up in the driveway to make sure there is no air in the cooling system. I have also changed the thermostat. I am running a 180 degree t stat. I am not sure what else to check. The water pump is new and water is circulating. The temperature gauge is a factory aftermarket gauge from our host. Thanks for all responses!!

 

[coilover]

If you still have the old T-stat you pulled out try removing the middle plunger which leaves about a 7/8 hole. Test with this as it will absolutely confirm or disprove it being T-stat related. I don't like to completely eliminate the stat as this lets the front and rear of the head run at two different temps which a 235 head sure doesn't need.