Thermostat and gasket - Mercruiser 350 Magnum

[mattias]

I started my 240sd last weekend and got an alarm after about 15 minutes that the engine was running hot? I shut it down immediately and now troubleshooting to find out why - was told to replace the thermostat. I'm in the process of doing this - check out the picture of the "old" thermostat, looks old and pretty rusty to me. What are you opinions of this being an issue. Also, I have never changed a thermostat before - are these gold colored tabs just part of the old gasket? Can i just scrape them off?

 

[Lazy Daze]

Has this always been a fresh water boat? What year 240SD? When was the last time it was replaced? Same question about manifilds/risers.

Why the "?" about running hot? Are you not sure? What troubleshooting have you done so far? Telling us that will help.

The rust is not from the t-stat - it's brass and SS. The rust (and the debris seen there) is from the engine. And, sure, that can affect it. Check the operation of the t-stat in a pot of water on the stove (google for more info). That will at least tell you if it is operational or not and give you more guidance.

The brass contacts are part of the gasket - they electrically mate the housing to the block side. The surfaces (both) must be completely clean and smooth before reinstall.

How does the impeller look? That's another very common maintenance item that can cause the same issue.

 

[mattias]

It is a 2005. We just bought it after the sea trial in Oct. (all was fine). Boat was a 1 owner always on the Ohio river (fresh water). I am not sure the last time this was replaced - may be the original one.

Where is the impeller for me to also check out?

 

[Bt Doctur]

located on the front of the engine