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Old 03-24-2014, 04:54 PM   #2
DavidM
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City: Litchfield, Ct
Join Date: Aug 2012
Posts: 6,785
I just did a coolant change on my Yanmar 6LY. You are right, there is no mention of a drain point in the service manual that I could find. But boatdiesel was helpful.

On mine there was a petcock on the main heat exchanger and one low on the starboard, aft side of the block. The one on the heat exchanger drained easily, but the one on the block was plugged with coolant residue and since it was hard to get to to clean out I ignored it. The gurus on boatdiesel said that the heat exchanger drain would get 80% of the coolant out- 4 out of 5 gallons. So that is what I did.

The heat exchanger drain on your 4LH should be obvious so if that is all you can find then like me you should be alright.

It will take a while to get all of the air out after you refill. I filled as much as I could, ran it at the dock until the coolant was warm and topped it up as well as the overflow tank. Then went out for a run. When I got back the overflow tank was half full and when I removed the cap there was coolant up to the top, so it was good and full.

David
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