TOPIC: Thermostat question

1958 Johnson RDS20 35hp. Bought the motor for a song and put in a new water impeller. I've done a couple hundred of these without issue so everything is installed right. turning right direction tubes all connected etc. Ran the motor for about a minute and it was starting to get quite warm to the touch and no water coming out of the exhaust so I shut her down. Removed the lower unit again just to check all my work and it's all good. Flushed water lines and there were no obstructions. I removed the thermostat only to find that the 60 year old part was stuck and rusty. Go figure, thing should have lasted over a hunnerd yrs. The poppet ball is nice and springy and sealing good. Would the old thermostat cause the overheating? Reading online and I really should not run the motor without the thermostat so I ordered a new one.

Yes - a thermostat can be stuck open or closed. A closed one recycles the water through the engine and blocks or restricts fresh cooling water from going into the engine. Also possible that there are chunks of debris or broken impeller plugging up the works.

Thanks Bruce. I flushed out all the lines and they were all clean and clear. Just waiting for the new stat to come in the mail.