The 455 I have in my cutlass is not a 1970 and I am not for sure what year. I do know it came out of a big car such as a 98 and I know it is a low compression 455 with dish pistons! Should it have a bypass hole in the thermostat? The temperature gage is a positive gauge that comes off of the front of the intake manifold. But it will fluctuate between 190° and 220° back-and-forth pretty often! Any replies are greatly appreciated!

 

First things first, are you sure there is no air in the cooling system? No leaks? Does the heater blow hot air consistently? Are you positive the gauge is accurate? There is no need to drill a air bleed in the thermostat, the bypass hose will allow trapped air to go around a closed thermostat.

Jack up the passenger corner of the car as high as possible with the radiator cap off. Let it sit overnight, if the coolant level dropped any there was air trapped in the system. Once the simple stuff is checked out, put a new thermostat in it. That’s the cheapest/most likely culprit other than low coolant level.

 

No air in system, probably sticky thermostat then. Heater is always nice and warm, never blows cool or cold! Thanks for the reply!

 

If it is not a rapid fluctuation, I agree its probably a bad thermostat.

 

is a 10 year old thermostat from Autozone! That probably tells the rest of the story! Thank you for the reply!

 

How old is the coolant?

 

@3 years old