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Old 01-28-2019, 11:13 AM   #1
City: New Bedford
Join Date: Sep 2015
Posts: 20
Transmission Cooler Change


I have a basic and general question. My boat (05 Mainship 40 Trawler, twin Yanmer 240's) is on the hard and winterized. I'd like to pull one or both transmission coolers. Of course, they are part of the raw water circuit. When I disconnect the raw water hose from the inlet/outlet of the cooler, some/all of the antifreeze in the raw water circuit will drain. Is this a problem? The engine will be left cooler-less and potentially drained of antifreeze for a few weeks minimum. Is it bad for the other components in the raw water circuit (other coolers, waterpump/impeller, etc) to be dry or not completely filled? The worry would be about losing any corrosion inhibiting benefits of the antifreeze. This seems like an easy cooler to get my feet wet with, but before proceeding I need to have an understanding of whether or not leaving the system drained/partially drained is a problem.

Thanks for any info!

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Old 01-28-2019, 01:01 PM   #2
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City: Litchfield, Ct
Join Date: Aug 2012
Posts: 5,863
Well, I am a little confused. You must be speaking of a winterized raw water system left filled with antifreeze for winter, since you are in New Bedford, Mass, right?

So don't worry. Let whatever antifreeze will drain out, drain. The raw water components are made of robust metals and won't be harmed a bit. Do make sure that you elevate or plug the tranny oil hoses so they won't drain oil.

You say you are jumping into the tranny cooler first. Yes, that is one of the easiest but also probably the one least likely to need service. If the after cooler never has been serviced it needs it the most as the consequences of failure are severe. Search for articles on this forum about after cooler servicing (I originated one on the Yanmar 6LY) and read Tony Athens articles on servicing the Cummins aftercooler at Here is a thread on the 4LH:

And if you are ok removing the after cooler but are leery about disassembling, cleaning, reassembling and testing them then Seaboard Marine at will do them for a reasonable fee.


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Old 01-28-2019, 01:05 PM   #3
City: New Bedford
Join Date: Sep 2015
Posts: 20
Yes David. You understand the situation correctly. Thanks for reassurance on letting the antifreeze (in the raw water system because it is winterized) drain. I'll check out the info you pointed to regarding the intercooler.
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