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Running without a thermostat 74 70HP

R

R F

New member
I have a 74 70 horse jet drive that I just go back in the water. I have ether a stuck open thermostat or no thermostat. Just how important is a thermostat ? I do not run in cold sea water.
 
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(Thermostat Purpose)
(J. Reeves)


Many engines are considered high performance engines and demand a thermostat(s), and many smaller hp engines also require a thermostat for the following reason. The pistons actually distort/twist off round when running. The thermostat is required to keep the outer wall surrounding the steel cylinder, and the cylinder wall itself at a temperature to compensate for the distortion.


With the thermostat removed, the difference in temperature between the inside the cylinder and the water jacket quickly reaches a point whereas (in effect) you have a oblong piston running up and down a round cylinder, or vice versa. Bottom line is without the thermostat, the piston and cylinder wall could be damaged in a short period of time.

The thermostat in your car isn't there simply to have the heater function properly..... think about it.
 
R F said:
I have a 74 70 horse jet drive that I just go back in the water. I have ether a stuck open thermostat or no thermostat. Just how important is a thermostat ? I do not run in cold sea water.
Click to expand...

Just wondering, how do you know it is missing or stuck?
 
I put the boat in 52 degree sea water----start the motor cold--plenty of water output right off the first second. I was going to stay at the dock until I was sure the thermo opened but with that much output even at idle I shoved off. I've run other jets and you have to wait a bit before you get output--but maybe I'm not familiar with the cold start water output of this model---if so then the thermostat tests okay as I was running for more than 1 hour.
 
At such cold water, the thermostat may never open at idle speeds. It simply isn't producing enough heat to raise the temp up to 140 degrees.

Besides, it should always discharge water any time it is running, whether 'stat is open or closed.
 
Thanks for that bit of news--I was worried that it was just such a case (always puts out water even cold idle)-but don't worrie she was running sometimes at 70% throttle and going just shy of max speed for miles-you just saved me an unessisary r&r
 
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