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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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Diesel This is a forum dedicated to diesel engines and their applicable accessories.


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Old 01-05-2014
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Going from Fresh Water Cooled to Raw Water Cooled

I have a Yanmar 2QM20H RWC that was converted to Fresh Water cooled. It has about 2000 hrs on the meter. The thermostat was never changed over to a FWC thermostat so it has always been run at a low heat temp. I don't believe that the FWC and RWC thermostats are the same and it occured to "why not just switch it back to Raw water cooled?" The plusses would be:
Having only one ready accessible water pump impeller, right now I have to remove the Altenator and brackets to get to the RW pump to change the impeller, more room in the engine compartment, ie, fewer hoses, no HX, not having to clean out the HX and possibly less maintenance.
What's the downside? Thanks.
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Last edited by Froggy; 01-10-2014 at 01:56 PM. Reason: Photo added
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Old 01-05-2014
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Re: Going from Fresh Water Cooled to Raw Water Cooled

The main downside is a raw water cooled engine simply will not last as long as a fresh water cooled engine, everything else being equal.

More so in a salt water environment. Less so in a fresh water environment.
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Old 01-05-2014
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Re: Going from Fresh Water Cooled to Raw Water Cooled

Given that someone went to the effort at some point, I'd assume the boat is in salt water.. if so going back to RWC makes no sense and can lead to corrosion of cooling passage walls to the point of failure.
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Old 01-05-2014
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Re: Going from Fresh Water Cooled to Raw Water Cooled

Many/most diesels "from the factory" come equipped with a heat exchanger. Unless you are always in fresh water, suggest you keep the fresh water cooling system. Salt is nasty stuff.

Paul T
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Re: Going from Fresh Water Cooled to Raw Water Cooled

Agree with everyone else...leave it FWC. Just leave the current T-stat in.
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Re: Going from Fresh Water Cooled to Raw Water Cooled

Four out of four.
The FWC stays! Thanks for the imput.
I think I'll switch the hoses for FWC water cooled pump to the RWC pump that way I can at least change out the RW impeller in a hurry. Thanks again.
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Old 01-08-2014
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Re: Going from Fresh Water Cooled to Raw Water Cooled

I would keep the exchanger as well. But I would certainly change the thermostat to the proper one for a fresh water cooled engine. Engines should be run at 170 to 180 degrees F. If raw water cooled the thermostat is 140 F so there is no salt build-up in the passages but it is a compromise and not ideal. With fresh water cooling there is no reason not to change it.
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Old 01-09-2014
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Re: Going from Fresh Water Cooled to Raw Water Cooled

Just adding. I watched a 15 year old Chevy 454 Crusader, that had been salt water cooled, get torn down once. The block was so corroded, it wasn't even rebuildable (hard to do for a Chevy 454 block). The mechanic doing it, who was a car racer, didn't even want it as a gift.

And, it had been running just a few weeks before that.
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