Overheating After Thermostat swap

[sub2010ss]

Good morning,
I got my boat all ready for the lake and was running it on the muffs. I wasn't seeing temperature come up above 100 after about 10 minutes of running so I picked up a new thermostat and temperature sender. The sender I found was an automotive sender. I get it all installed and run it again on the hose. Temperature comes up to 175, right about where I remember it running last year and I shut her down and load up for the lake. I get about 300 ft out of the no wake and temperature is up over 200. I give it a moment to settle down and it keeps climbing. I shut it down about 230. After cooling down and limping back to the doc between cool downs I get it loaded up and home. Now the only thing I can do to keep it cool is no thermostat. I tried both of the new and old thermostats again and temperature just keeps climbing. Without it doesn't hardly budge off of 100. Also note that my raw water pump was replaced last year, it's ran amazing all year, and my exhaust manifolds were cool even on the lake.

Today my plan is to
- test both of the thermostats in boiling water
- buy a new thermostat if needed
- pick up an infrared gun and check the block temp

Any other ideas or input would be much appreciated!

 

[Bt Doctur]

you either installed it improperly or the impeller is toast,unless your fresh water cooled 175 is a bit too high for a 160 deg stat

 

[sub2010ss]

Those were my first two thoughts as well. I double checked installation of the thermostat by looking at the drawings. Would the exhaust manifolds stay cool under load and motor stay cool without a thermostat if the impeller was bad?

 

[Bt Doctur]

the impeller is what sends water to the motor and manifolds . If the manifolds and risers were cool to the touch and the motor was hot ,either the therm was installed wrong or the engine circ pump shaft has broken

 

[Alumarine]

You mention you changed the sender.
Maybe that's the problem.
Have you checked it? What was wrong with the original sender?

 

[sub2010ss]

I was thinking possibly the circ pump as well.

I just bought a temperature gun, with the gauge reading over 200 the block was only reading 130. I open up the thermostat housing and the water is 130 as well. I'm now thinking the new themperature sender is bad. I assumed an automotive application would be the same. Maybe my assumption was wrong. My thermostat opens right about 170.

 

[sub2010ss]

Thanks for the replys!

The culprit was a bad temperature sender. Luckily this was an easy fix and I'm guessing I was never near 200 ever. After installing a new new sender, the temperature gauge is fluctuating between 175 and 130 and so is my temperature gun.