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My M38A1 will run all day around 140 deg at 30 mph. Once I speed up to 45 mph, the temp climes to 200 deg and above. It is the original radiator so I know (at the least) I need to re-core it, but before I spent too much on that or worse, a new radiator; I ask the following:

A) What should the normal operating temp be?
B) Will it take the same thermostat as a CJ5? (NAPA THM 530090)

Thanks,
Nate

160 to 180.

Sounds like you either do not have a thermostat installed or it is stuck open.

With the engine hot and running and the radiator cap off check and see if you have any indication of water flow (movement) that changes in amount with throttle changes.

Let us know if you also see a lot of bubbles during this check.

Check your timing also. The cooling system should still be able to make up for the timing being off though. Mine was pretty far off on a road trip last year - the temp climbed to around 200 deg on a long hill and didn't vary much for the rest of the trip (stayed between 190 and 200). I got back to camp and realized that I didn't tighten the distributor clamp down and the timing had changed. I re timed by ear because I didn't have a light and everything was close to normal after that.

Not saying that's your problem, but maybe it's time to check the timing anyway - worth looking at while you're checking the circulation in the radiator.

Thanks guys. I will give these a try tomorrow and let you know how it works. Thanks for the help