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Old 08-11-2012, 17:41   #1
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Convert Yanmar Raw Water to Fresh (upgrade?)

OK... I've got another thread going about a raw water exhaust manifold rusting through in the Maintenance forum... but:

I've just learned that there is a Yanmar 3GM30F in the boat yard here and has the freshwater cooling system that (in theory) bolts right onto my 3GM30 raw water engine block. I checked it out and it looks right.

Obviously I'd have to add the fresh water pump and some extra stuff (but it's all there on the other engine) and it seems to be in working condition.

So here's the rub:

I could spend $700 (plus duty if we're unlucky) getting the new raw water manifold and cover from the US and getting them to Mexico (where we are on the hard) or we could try to do this conversion to freshwater with what's available (used) here for far less money and perhaps is a better cooling system? The new system is more complicated (an extra pump, more stuff to break and to check on) and I like the simplicity of my old system.

Add to that: we have a 2 year old and are in a dusty toxic cheap boat yard and want to get away as quickly as possible (the new parts will be at least 2-3 weeks).

Anyone had both? Pros ans cons? Would this be a a true upgrade or just a lateral move to something different?
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Old 08-11-2012, 17:46   #2
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Re: Convert Yanmar Raw Water to Fresh (upgrade?)

Old raw water cooled Volvos seem to last. My gut says the fresh water cooling is a plus in the long run....
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Old 08-11-2012, 18:05   #3
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Re: Convert Yanmar Raw Water to Fresh (upgrade?)

I have a fresh water 3gm, but no experience with a raw water version.

Still, I think it would be an upgrade and you should consider the conversion. If you have confidence in those doing the work and the used parts are serviceable. For example if you need new replacements for the used parts that's going to gum up the process. Could be smart to disassemble the donor engine first. Also the hoses for fresh water might not be in the best shape and they are form-fitting so it's best to have the proper parts there.

I have an old factory service manual with an entire section on conversion from raw to fresh water. If there is any info there that might help I'd be happy to pass it along or scan a page or two and email them.
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Old 08-11-2012, 18:36   #4
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Re: Convert Yanmar Raw Water to Fresh (upgrade?)

I feel confident doing the work... no problem. I will make sure the parts are in working order tomorrow before I buy them. There are plenty of places to get hoses and clamps here in Guaymas (large port with a commercial boating industry). I would LOVE a few scanned pages on the conversion (though it looks to be quite straight forward).

Mostly it will come down to the condition of the new (fresh water) parts compared with waiting for new (and hugely more expensive) raw water parts from the US.
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Old 08-11-2012, 18:49   #5
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Re: Convert Yanmar Raw Water to Fresh (upgrade?)

An upgrade for less than the price of a repair. Could be a win-win.

Tomorrow I am demolishing a tile bathroom with a portable jack hammer. What fun, though I did go for a sail yesterday so it's all good.

In the evening I'll look at the manual for any info that might serve as a guide or warnings about process. And see what pages might prove helpful. I've looked at it before and recall it did look to be rather straight forward.
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Old 08-11-2012, 19:13   #6
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Re: Convert Yanmar Raw Water to Fresh (upgrade?)

The down fall of converting over once the motor has been run in salt water is age. The insides of a raw water system over time builds up little chunks of rust (iron oxide) which can plug up a heat exchanger core.
How many hours on the motor?

Before you install the fresh water system I'd take a look inside of the engine cooling capillaries to see if there is a rust build up. Either way you would want to do a major chemical flush of the salt water system w/o the thermostat before installing a heat exchanger. And I'd check the bearings in the engine water pump. See if there is rust coming out the bleed hole, between the bearings, on the bottom side of the pump.

And then you need to put the right antifreeze in for Yanmar so it doesn't eat the aluminum. And go full strength (50-70 mix).
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Old 08-11-2012, 19:46   #7
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Re: Convert Yanmar Raw Water to Fresh (upgrade?)

Thanks delmarrey. I did a vinegar wash and physical scrub of the raw water cooling cavity in the cylinder block this afternoon... hard to see in with the access to see if there is rust flakes. I'm sure there are some.

Question: when you reference the 'engine water pump' do you mean my raw water pump that I already have... or the additional fresh water pump that I would install during the conversion?
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Old 08-11-2012, 19:47   #8
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Re: Convert Yanmar Raw Water to Fresh (upgrade?)

Oh. and there are about 1500 hours on the engine. 200 of them are mine and everything was well looked after in that time.
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Old 08-11-2012, 20:10   #9
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Re: Convert Yanmar Raw Water to Fresh (upgrade?)

Probably the fresh water pump being referred to.

The weep hole on the bottom can indicate a seal going bad or worn bearings if water is weeping out.

The raw water pump, if like my Johnson, has no weep hole.
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Old 08-11-2012, 20:14   #10
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Re: Convert Yanmar Raw Water to Fresh (upgrade?)

Yes, I've never noticed any weep hole in my raw water pump.

Unfortunately the 'new' engine is far from mounted and working so I won't see any 'weeping' in the freshwater pump... but I will give it a thorough look over.
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Old 08-11-2012, 20:29   #11
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Re: Convert Yanmar Raw Water to Fresh (upgrade?)

The pump that came with the engine will be the fresh water pump after the conversion. The new raw water pump will be attached externally.

By pulling the original pump you'll be able to see into the cooling system a little using a flashlight.

If you have or know someone with a flexible wand inspection camera you could get a really good look. They're great for all kinds of tight spots on boats. I can even inspect my zincs without getting wet.

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Old 09-11-2012, 10:50   #12
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Re: Convert Yanmar Raw Water to Fresh (upgrade?)

Every post I have read regarding a conversion warned not to if the engine had over 3 years in salt water. Would I make a conversion if it was my boat??? Maybe!

A potential problem is salt saturates in the outer cast iron that causes a problem with antifreeze. What I have read claims the antifreeze turns to mush. I suggest you search for others who have actually traveled the conversion road to get real life experiences.

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Old 09-11-2012, 11:17   #13
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Re: Convert Yanmar Raw Water to Fresh (upgrade?)

I once purchased a boat which had an Atomic 4 converted from raw to fresh. PO said it worked great. I could not get over 3kts before engiine would over heat from day one. When I finally pulled the engine for replacement when my bank account came back to life after buying boat, I pulled the engine plates and block was full of rust scale. I would be very careful about converting from raw to fresh cooling. You don't say how far from US you are located, but why not just sail the boat back to US and get new parts here. What do you need the engine for anyway if you got sails?
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Old 09-11-2012, 12:57   #14
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Re: Convert Yanmar Raw Water to Fresh (upgrade?)

Turns out the guy wants more than I anticipated for the whole engine (he doesn't want to part it out even though its sat in a corner for 4 years).

I won't be doing the conversion. Thanks for all of the advice.
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