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Old 09-25-2018, 10:09 AM   #1
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Onan Coolant Leak

I have been pulling my hair out trying to find a coolant leak in my 8kw Onan genset. Recently, I pulled the heat exchanger and had it cleaned out at the local radiator shop. Replace a bunch of hoses at re-install, ran it for hours and all was good. Put sound shield back on and proceeded to use as normal for the remainder of the season. On our last trip, I opened it up to check oil and noticed some coolant in the bottom tray. I mopped it up and added some more, fired it up and checked for any obvious leaks, found none. I chalked it up to maybe I filled it too much and the coolant was from expansion. Left it and all was dry. 2 weeks later, was down at the boat and decided it was time to change the impeller, opened the sound shield and there was at least a quart or more of coolant in the tray. So, it's leaking from somewhere while not running. Checked all the hoses, connections, water pump, etc. and nothing.
I'm thinking that I need to pressurize the closed side of the system and check for leaks, just like a radiator in a car. Any suggestions, comments, advice?
Thanks!
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Old 09-25-2018, 12:22 PM   #2
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Probably a wrong answer, have the same genset. Thought I was leaking coolant, but no color. The pipe under the rear of the engine that moves sea water had rubbed through on the floor of the case. JB Weld to the rescue.

Possibly water pump? Most have a weep hole that begins leaking when the seals start to go.
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Old 09-25-2018, 12:39 PM   #3
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Yes, Pressurize it. I also vote for the weep hole in the coolant pump. Usually it means the bushing behind the seal is getting worn and the wobble wears the seal.
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Old 09-30-2018, 04:38 PM   #4
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Place some absorbent rag under the genset. run it, then look at the rag and see where on the engine it is leaking.

You do have a recovery tank correct?
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Old 09-30-2018, 05:44 PM   #5
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Also check the heat exchanger end caps. They can drip some.
Don't let any fluids remain on the floor of the enclosure. If they get blown into the windings of the generator, it can cause a total loss.
You don't want first hand knowledge of this, as I have.
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