Yanmar 3GM Overheating. Three Comments/Suggestions

Engines, Drive trains, Propellers, Steering, Ground Tackle and other mechanical system
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Knevins
Posts: 25
Joined: Sat Jan 10, 2009 1:38 pm

Yanmar 3GM Overheating. Three Comments/Suggestions

Post by Knevins »

Temperature sensor. Several years ago I had trouble with the temp buzzer sounding even at moderate RPM. Changed the fresh water, inspected the heat exchanger (OK) and replaced the water pump. Nothing helped. Finally, a more experienced neighbor explained that if you can touch the engine block, and if you don't hear water boiling, the engine is not overheating. Replacing the temperature sensor cured the "overheating".

Recent overheating at RPM over 3000 (after about 20 minutes) led to two other suggestions.

Flush the fresh water side. After draining the water/antifreeze I filled with fresh water, ran the engine to heat it up, and drained again. Did this three times until the drainage was almost clear. I think the engine to hot water tank holds a lot of coolant. I don't know if this really makes a difference, but it is easy to do.

Descale the raw water side. Rydlyme is a non-toxic weak muriatic solution. Will not burn skin, harm gelcoat, etc. Used a submersible pump in a 5 gallon bucket and one gallon of 50/50 Rydlyme/water. Pumped into the hose just after the water pump and recovered from the hose at the mixing elbow. I used garden hose and hose to 5/8 inch barb adapters to attach to the engine hoses. I ran the pump for 90 minutes. After completion the exhaust water was noticeably increased.

I should mention that the mixing elbow was replaced a year ago. After the above measures I ran the engine at 3400 RPM for an hour without overheating.

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Michel
Posts: 546
Joined: Sun Dec 07, 2008 5:48 am
Location: Zaanstad, the Netherlands, EU

Re: Yanmar 3GM Overheating. Three Comments/Suggestions

Post by Michel »

I used caustic soda to descale the fresh water side and there was a lot of dirt coming out. The PO's have probably fed seawater with lots of sealife from Mobile Bay to the freshwater system. With just flushing with clean water I would not have gotten the debris out. The caustic soda in my bilge also took off the greasy layer there.
Michel Capel, Freedom 44 #4 1981 'Alabama Queen', NED8188, cat ketch with wishbones, home port Enkhuizen, the Netherlands, 52*42.238'N 005*18.154'E.

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