89 Mercruiser 3.0 thermostat replacement

[natsgrampy]

Replaced my Alpha one out drive earlier this season. Still "breaking" it in.
Have run it for about 5 hours without any issues with water cooling the motor.
Today I ran it for about 15 minutes and watched the temp gauge climb right up to almost 200 degrees before I shut it down.
Have never had an issue with temp It always ran about 145 degrees.
Am going to replace the thermostat. Hope that's the cause. Any other causes possible?
When I replace it, do I need any gasket cement/sealant or does the new gasket go on dry?

 

[Bondo]

Replaced my Alpha one out drive earlier this season. Still "breaking" it in.
Have run it for about 5 hours without any issues with water cooling the motor.
Today I ran it for about 15 minutes and watched the temp gauge climb right up to almost 200 degrees before I shut it down.
Have never had an issue with temp It always ran about 145 degrees.
Am going to replace the thermostat. Hope that's the cause. Any other causes possible?
When I replace it, do I need any gasket cement/sealant or does the new gasket go on dry?

Ayuh,..... Did the new drive, have a new impeller pump,..??

I'd start there anyways,....

If ya do the T-stat, the gaskets go dry, the little rivet needs to make ground for the gauge,...

 

[Fishermark]

^^^ Yep. And when you check the impeller, if there are any pieces missing, the chances are good you will find them in the thermostat housing.

 

[natsgrampy]

Ayuh,..... Did the new drive, have a new impeller pump,..??

I'd start there anyways,....

If ya do the T-stat, the gaskets go dry, the little rivet needs to make ground for the gauge,...

I hope so! It was installed by a marine mechanic. It was an SEI 106, I was under the impression it was complete.

It ran with no problem for approx. 5 hours prior to today.

I'll start with the T-stat