I have a 327 in my 66 Chevelle and it seems like it doesnt want to heat up. I have the stock radiator with a 180 degree thermostat and a flexfan. At cruiseit only gets up to 150-160 degrees. I doesnt even look like the thermostat is even opening. When I got the car it didnt have a thermostat in it. Is the flex fan the problem? Should I replace it with a clutch fan?

Thanks
Steve

Either your temp indicator is defective or your thermostat is defective. If it was me, I'd drive 5 miles on the highway, pull over and carefully feel the upper radiator hose engine off. If its tight the coolant is hot. If not tight, I'd CAREFULLY remove the radiator cap, restart the engine, and stick a thermometer in the coolant. If it was less than 175* I'd conclude that the thermostat failed, in which case I'd drive over to the parts place and get a new 180 thermostat and gasket and replace thermostat. Fan got nothing to do with it

My $0.02

Hmmm, I am pretty sure you don't want your themostat to open until it reaches it's designed temp. That is it's purpose, to stay closed until the anti-freeze in the engine reaches running tempature and then it opens to allow the cooling system to open the flow of cooler fluids from the radiator. It helps the engine get to running tempature quicker and helps it maintain tempature then if no thermostat where there at all.

I would highly suggest you run by a radiator shop and ask them if they have an I/R gun. That will give you the most accurate reading of your temp.

Here is a thread that talks about what you might be experiencing:

http://www.chevelles.com/forums/showthread.php?t=115910&highlight=running+cool


Might want to boil test your thermostat as well.