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Old 01-07-2013, 13:17   #1
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Yanmar Heat exchanger leak??

I have a 1996 4jh te (serial #12285) and think the heat exchanger may be compromised. Hereīs what happened. Started with a big mistake - we tried to fill the hot water heater heat exchanger lines at the hot water heater using a hose and a T fitting. (hot water heater is above the engine). We heard fresh water running into the exhaust system at the water muffler. As soon as we heard it, we turned off the water and realized there was a serious problem. Ended up pulling the injectors, shutting off the fuel and then slowly turning over the engine. Sure enough - water was forced out of the injector ports. Since it was all the ports, not just one, Iīm assuming the head gasket is OK and the water got to the cylinders via the exhaust valves.

Reinstalled the injectors and then started the engine. Ran fine. Let it run for 1/2 hr, shut it down, then repeated a couple times to make sure all the water was out and everything is running OK.

My guess is the heat exchanger is compromised allowing fresh water to cross over to the raw water side and into the exhaust system. I canīt think of how else water got into the exhaust system. By using a hose (~30psi) I forced fresh water across to the raw water side, into the water muffler and then back up into the engine through the exhaust. Dumb, but inadvertently found a problem I didn't know about.

Other data:
- coolant level in the heat exchanger does not drop
- no visible leaks into the bilge
- no water in oil
- no detectable levels in any of the fluids (water, oil, transmission, etc)
- engine runs fine, does not overheat

Questions:
- how do I test the heat exchanger?
- what else could allow water into the cylinders
- if itīs the heat exchanger, do I need to replace the core or the whole assembly?
- If just the core, what else should be checked/replaced at the same time?
- what am I not asking that I should be asking?

Thanks!
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Old 01-07-2013, 13:49   #2
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Re: Yanmar Heat exchanger leak??

City water pressure could be as much as 50 psig. But having said that I find it at the edge of credibility that a leak in the heat exchanger would pass that much water. It must take several gallons to fill up the lift muffler and back up into the exhaust manifold.

But having said that, I don't see any other explanation.

First pull the end cap, the one forward. It is easy to get to and look inside. If ok then pull the aft one, harder to get to. One or the other should show severe corrosion.

If that doesn't show anything then do a pressure test of the coolant side.

Go to your local autoparts store. Buy (or rent- Advanced Auto rents a nice one) a cooling system test kit. Pressure up the coolant side. With that much leak you should hear it immediately. Then pull the heat exchanger and see what is wrong. I suspect that it is severely corroded at the tube sheet and the whole thing needs to be replaced. Won't be cheap as that exchanger is part of the exhaust manifold.

David
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Old 01-07-2013, 13:56   #3
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Re: Yanmar Heat exchanger leak??

Yeah - right at $2k for a new heat exchanger assembly. It doesn't make any sense to me either, especially since I'm not apparently losing any coolant. Unless the raw side is high enough pressure to only let water flow from raw to fresh. But then it would seem the bilge would fill up as water ran out the HE overflow (no expansion tank, just an overflow tube).

How hard is it to replace the assembly?
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Old 01-07-2013, 14:35   #4
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Re: Yanmar Heat exchanger leak??

There are O-rings on the ends of the heat exchanger core that form into a chamfered edge of the HE/Exhaust manifold body. The city pressure could have pushed past these O-rings temporarily. How you got water into all the cylinders is the real mystery as not all of your exhaust valves will be open at the same time. Maybe 2 of the 4 but no more.

Are you sure your hoses are correctly connected? Also, cannot really see how water would get into all the cylinders if not. Is this boat new to you?

BTW, you need to install an expansion tank above the water heater so your system will naturally bleed itself. This also will allow you to properly fill the system.
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Old 01-07-2013, 14:43   #5
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Re: Yanmar Heat exchanger leak??

Hmm. I wouldn't bet the ranch on all 4 cylinders. When the engine turned over, we held a cushion over the top of the ports to try and prevent water from spraying all over the engine room. That didn't work. Water sprayed all over bouncing off the bottom of the cushion. So I assumed all cylinders were full. Maybe only 2 were?

I have been questioning if the hoses from the water heater are hooked up right. Came this way from the PO and it's been too low on the really long refit list. We've finally reached that point of the list so started looking into it.

Am really glad I didn't screw it up so badly that 'new engine' was the next entry on the list.....
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Old 01-07-2013, 14:55   #6
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Re: Yanmar Heat exchanger leak??

Ok. Not all cylinders is good. I would buy new O-rings for the HE. They are cheap and fairly easy to replace.

I can tell you that unless the HE/Exhaust manifold has recently been replaced you will need to soon. The wall thickness in those original HEs were very thin and would corrode. Symptoms include AF smell from exhaust and a very slow usage of coolant over the span of weeks.

BTW, never use external pressurized water directly on any part of the cooling system.
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Old 01-07-2013, 15:02   #7
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Re: Yanmar Heat exchanger leak??

What's AF - antifreeze?

I don't think the exhaust manifold was ever replaced. Don't know for sure since we only bought the boat 2 yrs ago.

Sounds like my winter list for '13-'14 has started already!
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Old 01-07-2013, 17:40   #8
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Quote:
Originally Posted by Paperbird View Post
What's AF - antifreeze?
!
Yup, it is.
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