TAMD41P over heat alarm

I've got a 1997 Mainship 350 with twin Volvo penta TAMD41P engines. When I bring the engines up to WOT or close to it the starboard engine over heating alarm sounds and goes out when I bring the engines down to 1/2 throttle. The temperature on both engines are equal around 140-150 *. Where are the temperature alarm sending units? What temperature does the alarm supposed to sound? It doesn't appear to be overheating. Suspect a faulty alarm sending unit. I was going to swap sending units from engine to engine if they are easy to get to. Any thoughts? The water pumps have new impellers. Thank you. Dave.

What you are experiencing sounds like a cooling system that is working properly, but is being deprived of sufficient sea water. Suggest you check the seawater intake for obstructions.

If it's not the sending units, I would suspect a cooling system clog issue. I would start by circulating Barnacle Buster through the RW side of the cooling system and see what that does.

Do a search for this. Flyright did a good write up on his successful coolant system flush.

Have a play with a infrared thermometer gun,compare the two engines,hopefully that should show up your problem.If the temps as similar I'd do the sensor swap thing.It's happened to me a couple of times.

There are two relevant sensors: Gauge transducer and alarm switch. Both up on front of cylinder head in a housing for thermostats. Can't remember exactly where they are.

The alarm going off at high power may mean you do have a real overheat, and that gauge is the one that is off. Shoot tstat housing with temp gun, should be 180-190 at high power, tops.

Alarm setpoint I think is 100C, but memory is foggy. Often side of sensor is stamped with setpoint.

Post some pics of front of engine.

I'm with previous post that your engines both should read around 180. The engine alarm may be real. Your water temp readings are probably bogus.