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Old 11-07-2015, 17:47   #1
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Location: Cambridge MD
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Yanmar runs hot

My Yanmar runs hot. It started doing it around 2800 RPM then slowly dropping the RPM to now being down to 2200 when it starts to over heat. If you drop the RPM's 200 to 2000 the temp will drop back to normal. New raw water impeller new anti freeze. I am thinking the mixer may be clogged. Anyone have any other ideas?

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Old 11-07-2015, 18:17   #2
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Re: Yanmar runs hot

Hi DL,
Is it down on power? Is it making oil? Is there plenty of water coming out of the exhaust?
Start at the easiest part and work your way through it.

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Old 11-07-2015, 18:37   #3
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Re: Yanmar runs hot

Power is good oil good hard to tell about water when running at 2200 RPM. Today it dropped from 2500 to 2200 in about 5 hrs. as long as I stayed at 2100 it was normal which according to book is 165.
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Old 11-07-2015, 18:55   #4
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Re: Yanmar runs hot

Verify that the raw water is not blocked and that the raw water passage in the discharge elbow and the 90 degree fitting connected to it (if you have a U bend) is cleaned out.

The water passages on the discharge elbow get limed up with "stuff" as the water hits the hot exhaust. I use a bike spoke to clean out the passages.

Could also be the thermostat or the raw water impeller. . But I'm betting its the discharge elbow as your symptoms tend to lend towards that.
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Old 11-07-2015, 19:55   #5
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Re: Yanmar runs hot

Very easy to miss an obstruction in the raw water intake. I spent days unsuccessfully cleaning filters, replacing the impeller, testing the thermostat, doing flat-out runs to test etc etc. Then I finally found a bit of hard marine growth right inside the inlet hose. I had back-blown it and prodded through with a screwdriver etc, but the little bugger was still in there.

Cheers, Graeme
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Old 11-07-2015, 20:45   #6
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Location: Saskatoon, Canada & Eastern Caribbean
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Re: Yanmar runs hot

A Lagoon 420 we chartered with 40 HP Yanmars was overheating on the port engine. The charter company told me they solved the problem with an acid flush on the raw water side of the system they told me later.

Same scenario, it would behave when running lower RPM's and the water flow out of the exhaust seemed normal amount.

Best of Luck.
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Old 12-07-2015, 04:00   #7
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Location: Nelson NZ; boat in Brisbane
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Re: Yanmar runs hot

New impeller.......New impellar may not be doing the job properly.
Could swap it over and see if anything changes.

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