I tend to agree it's probably a dirty or clogged radiator causing the poor cooling, but best to be sure before going to the expense of replacing it.

You can simply remove the thermostat to check if that's the problem, it should run cool after you take it out.

And you can drive it without the T-stat, but best to replace it as soon as convenient so the engine runs at optimal temperature.

If not, most likely it's the radiator (I like the rockauto part, great price and no tax, plus excellent service).

But first you should make sure the cooling fins are clean on the outside. Blast it really well with a garden hose and pressure nozzle and see if that helps.

If either of these work you've fixed the problem for free with about 15 minutes work.

If they don't work and your radiator is original and/or looking pretty old, it's probably time to replace it.

 

I am pretty sure you should not run without a thermostat. If I remember correctly, this has a bypass around the radiator that is open when the thermostat is closed. This ensures that there is some flow through the engine (to let the water and thermostat heat up so it will open). When the thermostat opens it closes the bypass. If you operate without the bypass much of the water will bypass the radiator and you will lose cooling capacity.

The only way to operate without a thermostat is to plug the bypass opening. I think you can thread it for 1/2" pipe plug and install a plug. That is what is done on my ITA race car.

If you want to see if it is the thermostat, just buy a new one and test it in a pot of boiling water to make sure it opens. Then install it and see if your temperature is lower.

The most likely problem tho is a dirty radiator.

Carl

 

I should have added that you need to make sure that the thermostat you install (or have installed) is a bypass style. See attached pictures.