1992 SN overheat - tried everything

Yes.

Check t-state in pot of heated water with thermometer. Observe at what temperature it opens up.

Check the electrical connections (especially) grounds between sending unit and temperature guage.

If the impellor had blades to break off, there is a good chance you have some stuck in the block restricting water flow. When mine broke off I found three in the exhaust manifolds and one in the bypass fitting behind the thermostat. They can't pass down the veins in the exhaust manifolds.

I'm thinking upside-down t-stat. Is it possible, dimentionally?

I'm pretty sure I got that t-stat in correct. The pointed end goes up - correct?

Get a 142 degree t-stat. That will bring your temperature down.

79nautique:

The part I didn't bother to mention at the onset of this post was that this whole thing started because my temp was soaring up over 200. The old t-stat that came out was shot (and I had some old impeller parts in the t-stat housing from the previous owner). It was so old that I couldn't read the temp markings on it to know what it was. I put in a 160 because that is what skidim recommends, as well as many people on this forum and PN forum. So I agree, if it ain't broke don't fix it, but this was "broke". Chances are that everything is fine now, but it still makes no sense to me that I'm running a 160 t-stat and the gauge is showing 180? Until I know why, I'll always be a little suspicious that something else isn't quite right.

ccskier16:
Good idea to go to a 142, but that will just mask the problem and doesn't fix it (if there is one).

Thanks for all the input from everyone. I have learned a lot from this forum and PN. I also learned a lot more about my boat and how the cooling system works. If anyone else has more ideas, please send them my way.

Chill99,

It was news to me, but I was told by the dealer that the 143 degree thermostat is what is recommended for our boats. I believe it should allow the motor to run ~160 degrees.

Your 160 deg thermostat is whats causing you to run warm. I think 180 degrees is just fine for the motor if you dont want to bother changing it again.

It does sound like there is blockage, not a thermostat prob. No reason it should run that hot with a 160 thermostat.

Try taking off every hose in the cooling system and running water through them with a hose backwards, it may dislodge something which is positioned just right where it will not pass though.

If this doesn't change anything I would pop out all of the freeze plugs and see what is in the cooling jackets around the bottom of the motor. Sand and rust can accumulate there and really screw with cooling issues, and maybe some of the pieces from the old water pump.