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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 11-09-2009
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Yanmar Heat Exchanger

I hope someone can help me with some tips to pulling the core from my heat exchanger.

I have a 2gmf that appears to be lossing anti-freeze from the closed side of the exchanger. So I figure it's got to be leaking from the closed side into the exshaust side. There's no water in the oil, no steam in the exshaust, and the water will disappear over the week, can't find an external leak anywhere.

So it has to be the heat exchanger right?

Right now I have both end caps of the exchanger off and the core will not move. I have left it attached to the engine. I'm hoping not to have to pull this off the engine.
I've tried tapping with a dead blow hammer (rubber tipped) The info I found said to push it out from the back to front. And to tap it will said hammer if stuck.
Is there something I'm missing?

Does anyone have any tips for removing the core without removing the exchanger from the engine.

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Old 11-13-2009
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Well since I didn't hear from anyone with any tips I pulled off the heat exchanger. Here's how I did it.

First you have to undo (loosen off) all 6 hose clamps. Make sure the anti-freeze is drained

Then the fuel line from the primary fuel pump to filter had to be removed.

Next I undid the throttle linkage. You can leave the mixing elbow on if you like.

After that it was just a matter of undoing the 6 bolts and pulling the exchanger off the block.

The core wasn't as easy to pull out as I was led to believe. I had to use a brass drift and drive it all the way to get it out.
Now that it's out i can replace the o-rings and gaskets.

Last edited by Hunterdon31; 11-14-2009 at 10:38 AM. Reason: included instructions for removal
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Old 11-13-2009
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Thanks for the update, Don. Could you keep us posted on how this goes? I've got a 2gm20f and might be facing this in the near future. Always good to hear the details from someone doing it.
Tom K

2000 Beneteau 331
Northern Chesapeake Bay

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Old 11-17-2009
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Thanks YachtDavits
Just priced out a new core from Yanmar. 1000-1300 USD Ouch. I'll call around and see if anyone can test this one for me. The boat will be sitting on the hard for the next 6 months until the lakes thaw out.
Thanks Don
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Old 11-17-2009
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Very doubtful there is anything wrong with your "bundel" it is all copper construction and built very well.
Have it pressure tested at a radiator shop that also works on marine heat exchangers.

They well soak it over night in a mild acid to descale it before they work on it and the whole process should be less then 75 bucks if no repairs are needed.

Heat exchangers being aluminum will suffer over the years from electrolysis and should be fitted with a sacrificial zinc. many however will drain down and not hold much of any raw water so as mentioned by a previous poster his has had no ill affects after 20+ years.

I had to rebuild on mine this year but the bundle passed with flying colors...mostly around the hose barbs which we cut off and replaced one of them completely and some exhaust gas erosion unrelated to electrolysis around the exhaust flanges which needed attention.

If you look close you can see the new hose barb welded on the far end...the others were serviceable but probably dew in another 10 years if the engine makes it that long...welding on pitted and contaminated aluminum is difficult so you don't want to if you don't have to.
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Last edited by Stillraining; 11-17-2009 at 01:54 PM.
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Old 11-24-2009
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2gm20F leak into heat exchanger unlikely

Don, I've had my boat and it's 2gm20f for over 20 years, and once I thought I had the problem you describe. Note that raw water goes through the core tubes, and fresh water circulates around the tubes--inside and outside of the cylinder. I think it unlikely that there is a leak in these components which could result in fresh water loss. The leak would have to be in either a tube itself or one of the two end plates that the tubes go through. As already said, the tubes are solid copper, and they are pretty thick. There could be a leak where a tube goes through one of the plates, or in a plate itself, but you would probably be able to see this.

A simple test of the core seems possible since it is out. Drain and dry the core completely. Add water where the fresh water would go (inside the outer cylinder, not the tubes), tape up the big holes where freshwater enters and exits the cylinder, and let the core stand in various positions for a week or so. If you see any water coming out of a tube, you have a leak. If there is no water coming out of any tube, your problem is elsewhere. (I don't think a pressure test is necessary for the kind of problem you describe).

A thought on what might be your problem: If you had drained, cleaned, and refilled your freshwater system (which is a good idea every couple of years or so), you might not have removed all the air out before you restarted the engine. Air is a particular problem when the fresh water system has a long run to a water tank heat exchanger. The freshwater moves with very little pressure, and there are lots of bends in the whole system, so it can be hard to force all the air out the top. So, after the engine has run a bit the air may only have moved around. You can even have an "airlock" which causes the system to overheat. The reservoir is empty and no water is visible when the cap is opened--it is easy to mistakenly think water has leaked out.

Note that if there is a freshwater leak that is not in the heat exchanger there should be evidence under the engine or elsewhere in the bilge. (If water was leaking inside the engine it probably would have caused a fatal event by now--and you said the oil and exhaust looked free of moisture). So if you don't see anything outside the engine, it's pretty much has got to be an air problem.

A final suggestion. Scale (particularly if your boat sits in salt water) will accumulate whether you use your engine or not. The accumulation may actually be worse if raw water just sits in the tubes for long periods of time without moving. The scale can be hard to see since the inner diameter of the tubes is small. A cleaning with acid and a checkup at a radiator shop is a good idea after about ten years. I think I paid $125 the last time. I have also poured muriatic acid through the raw water side a few times, and you don't have to remove the heat exchanger to do this (disconnect both engine connections, use two pieces of an old cut garden hose long enough so you can stand at the dock, a funnel, gloves, and eye protection; use one of the hose ends to force tap water through as a rinse after 15 minutes or so). Either way, it does make a big difference.

Good luck.
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