Slow Overheating

[Moody46CC]

I have a 6kw Mastervolt Genset. The engine is a two cylinder Mitsubishi. Over the last several years, it has given me a lot of problems with overheating. It has coolant and exhaust sensors that shut it down when it reaches a safety point. That would occur once the engine warmed up--say 10 minutes. Back flushed it, checked the usual (impeller, thermostat), even had the heat exchanger bathed in some sort of acid solution to get rid of scale and build up. In putting the boat in commission last week, I installed a water temperature gauge on the Mitsubishi engine, cranked it and watched. Engine started immediately and ran well. I did some other work but every 5 minutes or so went and observed the gauge. Slowly but surely the temperature rose. After an hour and a half the temperature reached boiling and the engine shut down.

90 minutes so a real slow boil. Any ideas why? Oh---I never turned on anything that drew a load, so the rise in temperature was not affected by a load. Had there been one, things would likely have boiled sooner given the extra work.

Thanks.

[Bruce K]

Sounds like the raw water side of your heat exchanger needs a descale.

[Wotname]

Originally Posted by Moody46CC

......
90 minutes so a real slow boil. Any ideas why? .......

Well nothing specific but to say, the cooling system relies on three factors - go though each one until you find the culprit.

1. engine coolant circulating (engine water pump, thermostat, fresh water side of H/E etc).
2. Sufficient raw water flowing (RWC water pump, salt side of H/E, plumbing, inlet strainer, discharge point etc)
3. Heat exchanger (clean both sides and sufficient size).

As the problem is long term, what there a time when it did work OK? Perhaps something is undersized and worked OK when perfectly new but as time goes on, a small reduction in performance might be causing this slow boil.

[robert sailor]

All good advice, my go to on overheating is to look at my salt water flow out the exhaust, if I have lots of water I know the impeller is working. I pull the core and give it an acid bath, that usually solves the over heating. If that doesn't work it's not a waste of time because that core needs semi regular cleaning anyways. So you'd be left with the fresh water side.

[Moody46CC]

Thanks for advice. I'm going to have to measure the water discharge.