Volvo Penta MS 2V Overheating

[d-p]

I have an 84 C&C sailboat with a 27 horse, 3 cylinder diesel. It has started running hot after 2 or 3 hours of use. I have checked the thermostat, heat exchanger and the prop turns freely. Has plenty of raw water coming out of the exhaust, new inpeller 1 year ago. What else could it be? thanks
engine MS 2V

[Faster]

What specifically did you check about the H/E? are the tubes clear/clean? No impeller bits on the intake end? Odd that it takes 2 - 3 hours to manifest the problem... Mixing elbow clear? Any suction hoses aging and starting to collapse/pinch off flow? FW coolant levels OK?

[johnnyquest37]

How did you check the thermostat?

[Silvio]

I would replace the thermostat (cheap and easy) and open up the HE and clean it out as others have already suggested. Might help to know roughly where you are at also.

If your RW side is working you are likely either not exchanging heat or not circulating FW through the cooling system.

[d-p]

Tubes are clear. Still looking at the mixing elbows. If i run water in one elbow it comes out the other but won't filll any tubes up if I close the one and fill the other. Don't seem right?

[d-p]

pan of Hot water and thermometer

[d-p]

replaced thermost last year, checked it this Morning. I Am in Isla Mujeres, Mexico right now.

[d-p]

Is it correct that only raw water runs through the tubes?

[Faster]

Typically RW goes through the tubes and the FWcoolant surrounds the tubes, but it's possible to be reversed.. it would work either way if so designed. I believe most run RW through the tubes.

If your RW flow is adequate then the thermostat and the coolant level are the first things to ensure are correct. You could confirm your FW levels are good, then run without the thermostat as a trial and see if it stays (likely too) cool... If it still heats up there's a problem with your circulation, or the H/E is likely fouled or ineffective in some way.

Also possible that your temp indication is faulty and you're not indeed heating up.. but that's a risky assumption to make...

[sony2000]

Could it also be a sign that the raw water system has developed a layer of salt crystals, impeeding the transfer of heat. Desalination with various acids is the only way I think, but I'm a fresh water sailer.