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fresh/salt water heat exchanger on Yanmar for V-42

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Joined: 27 Jun 2006
Posts: 14

PostPosted: Tue Oct 02, 2007 12:19 pm    Post subject: fresh/salt water heat exchanger on Yanmar for V-42 Reply with quote

Good day all. Was wondering if someone has some info that may be able to help me.

Have the 44hp Yanmar with about 1300 hours and noticed it started consuming fresh water. Have been putting fresh water in the overflow container, about half a quart per hour to keep it from overheating. Had to let is sit a while as have been busy and when I went to open the cap, it had black slugde in the heat exhanger.

The house water heater, which can use engine water to heat drinking water is about 15 years old, but do not see any water leaking around the water heater, No leaks around the Yanmar itself either.

Have been told not to put anit-freeze in the heat exhanger as if the water heater exhanger breaks, you could get anti-freeze in your drinking water.


Is their sometime of anti-freeze material you can put in the Yanmar fresh water to keep it from rusting, but also not harmfull in case the water heater fails?

Is it much of a job to take the Yanmar heat exhanger off and have it cleaned up? If so any sugestions where to send it?

Has anyone seen a slow leak like this, with no visable seepage?

The Yanmar runs like a top, so do not think it is a cracked head or anything.

Thanks for any and all suggestions.

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Mathew Shankweiler

Joined: 04 Jan 2006
Posts: 56
Location: FL

PostPosted: Wed Oct 03, 2007 7:29 am    Post subject: Reply with quote

Taking the heat exchanger off should be relatively easy. Don't force anything and always use a WD-40 like rust inhibitor to loosen the bolts before trying to remove them. Any good yanmar certified shop will do a good job and it will cost about $100 for them to descale and refurbish the unit. I did mine along with my exhaust elbow and exhaust manifold about 1 year ago with great results. They did a wonderful job. I used Hawk Diesel in St Pete FL.

For yourself, take a picture of the engine and hose layouts before you start disassembling, so you can put it all back together. You might as well change all the hoses/clamps and bolts in that area when putting it all back together.

Black sludge in the heat exchanger? Is that black sludge in the salt water part or the fresh water part. You can tell this if you open your cap. The cap is for the fresh water/coolant and the zinc nut is for the salt water. If it is the fresh water side then you have seperate issues. First off, check your oil to see if it has mixed with water. It will look milky. If so, then get a mechanic. If not, then start by trying to run the hoses that go from the engine to the water heater, so that the hose bypasses the water heater and goes directly back into the engine. Drain your water and replace with fresh water and coolant, about a 80/20 mix should be fine. Run the engine for a while and see if the fluid turns color. if this works then you know it is your water heater.

You should always add some antifreeze in the coolant to prevent rust and if your water heater is in good condition, no antifreeze should mix with the fresh water due to the fact that they are completely seperated, no mixing occurs. On the other hand if your water heater is that bad off, it may have made the whole system black or at least rust colored. My water heater was severly rusted, but still work. When I removed it, its weight was about triple the new one and it was empty. Must have been all the rust!

If the salt water is the side that is bad, then you could have a serious back up in the exhaust elbow or a hole in the exhaust manifold or several other issues.

Good luck!
"Living on Earth is expensive, but it does include a free trip around the Sun every year."
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Joined: 17 Nov 2005
Posts: 103
Location: Deltaville, VA

PostPosted: Wed Oct 03, 2007 12:49 pm    Post subject: Reply with quote

Whoever told you not to put anti freeze on the fresh water side of the heat exchanger should be hunted down and beaten.

Do not worry anti freeze getting into your hot water. You should have a check valve on the water heater inlet that will keep it from contaminating the tanks anyway, and the anti freeze is detectable in very small amounts - way less than the toxic levels. If you are still worried, use the non-toxic propylene glycol type.

You need antifreeze (a 50-50 blend) for 2 reasons: Elevating the boiling point of the solution and inhibiting corrosion of the engine. In fact, it should be changed periodically to keep the corrosion protection active.

By running pure water in the heat exchanger, you are corroding the engine and it's parts. That's what the black crud in the HX is.

The tube bundle is removable without removing the whole exchanger: Drain the fresh water sdie down, take off the cover plates on each end and push out the tube bundle. You can then clean it with Marsolve or some other descaler/cleaner. Replace the orings when you put it back together.

As to where the water is going, it is either leaking into the engine (is the exhaust white at all?), boiling off through the radiator cap, leaking into the boat, or leaking into the water heater. You can get a pressure tester for the system (Auto Shack and Advance Auto will loan one to you) and find out where it's leaking to.
Frank Timmons
V42 Magic Dragon
Deltaville, VA
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Joined: 22 Aug 2006
Posts: 25
Location: Kansas City

PostPosted: Thu Oct 04, 2007 4:34 am    Post subject: Reply with quote

One possible location for your leak is the hoses that run between the engine cooling system and the hot water heater. If one of them is chafed through somewhere between the two ends, the water would find its way to the bilge and you might not see the leak at either the engine or the water heater.

If your leak is through the tube assembly, you will either have to replace it or have somebody locate and braze up the holes where it is leaking. I would just replace it if that is the case.
Patrick Harrington
S/V Stolen Child
Tayana 42 Hull #92
Web: www.patrickandnancy.net
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Rich Hampel

Joined: 15 Aug 2005
Posts: 391
Location: Chalfont Pennsylvania

PostPosted: Thu Oct 04, 2007 8:54 am    Post subject: Reply with quote

Sorry to say ... black sludge in the heat exchanger and loss of coolant = high probability of blown head gasket.
Easy enough to find out.... get a mechanic who can do 'black light' analysis of the cooling water. You dump in the 'flourescing chemical' into the water, let engine run for a few hours, use 'black light' on the water. If it fluoresces (to show high concentration of CO or CO2) ... you have a blown head gasket.
You dont need the mechanic to come to the boat to do this.... first find one who has the black light equipment, get the compound from an auto supply store (NAPA, etc.) dump in, run, etc. then take a 'sample' in a CLOSED container to the mechanic who can do this.

Diesel marine engines should have their head bolts routinely and periodically re-torqued .... saves replacing head gaskets. Has been this way ever since asbestos containing head gaskets were banned.

Such leaks are usually in two directions ... so I wouldnt wait too long in case water is also backdraining into the combustion chamber. At the least when shutting down th engine, remove/'crack' the 'radiator cap' to remove the pressure so that when the engine cools down you down 'suck' the cooling water into a cylinder, etc. (Dont get burned/scalded when 'cracking' the cap.)
Ty37 #423 "Aquila"
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