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post #1 of 6 Old 07-06-2011 Thread Starter
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Yanmar 1GM10 Thermostat and Temp Sending Unit

I have a 1GM10. I replaced the strainer, thermostat, impeller, and all hoses after purchasing the vessel last fall. For 3 weeks this season, the motor ran fine at 2400 RPM for extended periods. It was negelected and sat in salt water prior to my purchase. I flushed the engine continuously prior to replacing all the parts. The exhaust elbow appeared slightly corroded, but sound. I started overheating last weekend after running at 2000 RPM for 10 minutes. Pulled the thermostat to check for obstruction (none) and the temperature sending unit to check operation. The thermostat opens fully at 125F. The sending unit switches at 150F. Are these temperatures too cool? Automotive thermostats generally are 160F to 180F (although they are pressurized systems and the Yanmar is raw water cooled and not pressurized). I have ordered a new exhaust elbow to try next. Any other suggestions?
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post #2 of 6 Old 07-06-2011
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The thermostat for a raw water cooled Yanmar should be 140 F. Any warmer and salt deposits will form in the cooling passages.
Fresh water cooled engines run at 160 to 180.

You say the exhaust elbow seemed corroded. Did you remove it to see if it is clogged?

Brian
Living aboard in Victoria Harbour
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post #3 of 6 Old 07-06-2011
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How clean is the bottom and the prop? That can cause an extra load

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post #4 of 6 Old 07-06-2011
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As Brian says, raw water cooled engines are designed to run at about 140F to minimize scaling of the engine cooling passages. Do you have a good water flow out of the exhaust? If not, you have a restriction somewhere in the cooling circuit.
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post #5 of 6 Old 07-06-2011
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It could well be the injection elbow,and obviously you've checked the strainer but make sure the skin fitting is not blocked with seaweed,plastic bag old condom etc.etc. Good luck.
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post #6 of 6 Old 07-01-2012
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Re: Yanmar 1GM10 Thermostat and Temp Sending Unit

when engine is cold a closed thermosat limits water to engine sending majority of seawater out through exhaust. when engine is at operating temp the thermostat opens closing off water flow through exhaust and sends all seawater through engine then out through exhaust but on older engines the seal is not that good and some cooling seawater leaks past the thermostat were it seals against the engine and is allowed to flow through the exhaust circuit instead and starves engine of some cooling water and resulting in overheating at high loads or speeds. Being in a moderate climate my fix was to block water from entering the exhaust and removing the thermostat. Hindsight
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