CAT 340 Overheating/Running Hot

Greetings:

I have a 2008 Supra Launch 21 SSV with a CAT 340 Assault engine. I put in water this week and not long after launching the temp ran over 200 degrees which triggered a warning on the dash. I shut the bout off and checked the engine.

This happened once before when I sucked some muck up when I parked the boat on a beach and it worked itself through after alternatively running and cooling the engine.

I took the approach to running and cooling the engine this time and it has helped to a point where I can see the engine temp rise up to about 180 degrees then drops to 155 degrees then back up to 180ish and back down. After doing this for a while, I now have the engine stabilized at 160 degrees (which has typically been the engine temp on the hottest of days). However, the water is 58 degrees and the engine should be running in the 145 to 150 degree range.

I changed the impeller approximately 5 years ago but this doesn't seem to be the issue as the engine was alternatively heating and cooling. I'm thinking it might be the thermostat. I'm not sure where the thermostat is and hope it is accessible. Anyone have any other thoughts on what the issue could be?...thanks in advance...John

Five years on the impeller?? No way Jose, that would be the first thing I would check. Then the T-stat.
Two 25 hour seasons on my Rider and I found parts of the rubber impeller lodged in the T-stat. That’s a routine maintenance thing like changing the oil.

Especially if you don't remove the impeller over the winter months. First thing to check and also the cheapest to replace.

Replace that impeller. Betting that is your issue. I replace mine at the beginning of every season. Make sure you never dry start your engine. I see people start their boats on trailer before launching to make sure it starts and runs. That will kill the impeller very quickly. I run my boat on the trailer from a rubbermade tub with a connection for the raw water hose. This allows me to check and make sure impeller is working properly. If working properly it will just about rip a finger off. Good luck!

Thanks for the responses.

I replaced the impeller today and it seems to have helped. However, I think it is running a little warm still. The air temp was 80 degrees today and the water temp was 63 degrees. After installing the new impeller the engine temp fluctuated between 167 degrees and 153 degrees as I varied my speed from 3200 rpm to idle. However this still seems a bit warm...anyone have thoughts on this? The existing thermostat is a 160 degree thermostat. I may change the thermostat for good measure. Could anyone point it out in the picture below.

Also, I took off the engine cover (is this the manifold cover) and in order to do this I had to unplug the electrical connection shown at the bottom of the picture. I was hoping to get a better view of the where the rubber hoses come together at the top of the picture to see if this is the thermostat location. I put everything back together and went out to test impeller. At one point I idled down and the engine sputtered and stopped. it has never done this. I took a look at the engine and realized I did not plug the electrical connector back in. I reconnected it and started the engine and got a Service Engine warning on my dashboard...UUGGG! I continued to test the impeller and the boat ran fine however the warning didn't clear. Does anyone know what the electrical connector is? Could this have caused the error code? Is there anyway I can clear the code?...thanks for any help...John

I would not worry about your temperature or the thermostat at this point. Your engine temp is well within limits and you are looking for an issue to solve where there isn't one now. The thermostat is working and functioning properly if you are seeing a temperature swing like you posted above.

Attachment 18608

Here is thermostat location.

Mine runs 160 all day long.