Question to watertemp of a Diesel

[ak5609]

Hello.
My catamaran has 2 Westerbeke Diesel engines, each with 42 horses, maybe less cause they are old.
But they run ok and they sound ok, except on 1 an alarm goes on after more or less 10 minutes.
Both engines were not in use for about 6 months and my boat was in the water that time, when I cranked the Diesels for the first time again.
Now I realized that the water temperature of both engines thru the exhaust is quite different.
The water of the engine, which has the Alarm going on, is still cold after 10 minutes, basically has the same temp of the ocean water and is not getting warmer as the other engine has a Temp of 35-40°, which I consider normal.
My suggestion would be, that the heat exchanger might be clogged?
I still haven't used Muriatic, what some people suggested Prior as I am still too afraid of.

Otherwise there's nothing wrong with the engine. All belts are good, it sounds good and solid, but Off course there must be a reason for the Alarm going on.
The engine is not overheating regarding my impression ... which might be wrong.
Thank you for your help.

[boris]

I assume it is freshwater cooled?
I would start with a new thermostat

[a64pilot]

First determine the reason for the alarm, I believe it can be either oil pressure or coolant temp.
Buy an IR point and shoot thermometer and use it to see if the engine is overheating.
If your heat exchanger is clogged, it is clogged on the fresh water side and that takes disassembly to clean. If it were clogged on the sea water side, then you would not get water flow out of the exhaust.

It does sound like a stuck closed thermostat though, easy to change. A stuck closed thermostat is essentially a clog.

[Cheechako]

I doubt its a clog if the engine runs too cold! That would be just the opposite. I lean toward thermostat, although a bad one is pretty rare..... and it would have to be stuck wide open if the engine isn't overheating.
I second getting an IR thermometer and finding out if anything is really too hot or cold. One boat I had spent half way thru transiting the Caribe trying to diagnose an overheating issue. Turns out the sender was bad and the engine wasn't overheating at all. How does each engine compare if you test the block for heat with your hand?

[four winds]

Indeed it sounds like a thermostat stuck closed.

The freshwater side not circulating, getting hot and then the alarm.

The saltwater side flowing normally but not removing any heat.

Since the sender is in the freshwater cooling jackets it gets hot and trips. Yet the exhaust water is cool since it could not remove heat do to lack of flow in the exchanger.



I suppose the freshwater side of the exchanger could be plugged but that seems less likely than the usual salt water side.