Yanmar 2GM20F, Leaking Antifreeze, Heat Exchanger

Jun 1, 2016
156
Hunter 28.5 Lake City, MN
A couple weeks ago, I had the temp alarm go off on my 88 Hunter 28.5 with a 2GM20F. Found the antifreeze was low so I filled it up. I've been checking it and it keeps going down. (This is my second year with the boat.)

So, today I went up to the marina armed with a cooling system pressure tester and found that the system won't hold any pressure. I filled the anti-freeze up to the top of the neck and put on the pressure tester and the level of antifreeze goes down as I pump the tester handle. :-( I checked below the engine and there is no antifreeze that is collecting, and when running the engine, there are no bubbles or change in the level of the fluid as I watched it. I don't think it's a head gasket issue.

It seems to me that the antifreeze must be leaking out the heat exchanger into the exhaust, apparently out the back as there is no antifreeze that comes down the front inlet hose (raw water input). I was trying to study the installation and figure out how it is put together, to have a better idea of what I have to do to fix it. (I'm a fairly good mechanic, been rebuilding cars and even an Evinrude outboard V6 once!).

I'd like some coaching if there is someone that has been into this before, I'd really appreciate some advice. I found the coolant drain on the starboard side of the engine, mostly comes out brown!. I also found the lines that go back to the water heater (currently empty, I don't use it). What was in the water heater is clean water, no antifreeze.

Question 1: There is also two 5/8" lines that go from the heat exchanger outside of the engine compartment to some sort of white plastic vent valve, and back into the exhaust manifold mixer. What is this for??? (No apparent leak here either.)

Question 2: Will I need to pull the head to get the heat exchanger off? It doesn't look like it, but it is attached to the head. Also, will I be able to seal up the heat exchanger OFF THE ENGINE in order to find where it's leaking??? I'm not sure how to find the leak once I get it off.

Question 3: Will I need to remove the whole heat exchanger in order to fix it? Or can I remove an end?

I found a manual on line in another thread: https://sbo.sailboatowners.com/downloads/Hunter_gen_25628785.pdf

The boat get's pulled out of the water in about 2 or 3 weeks (our water will get this hard crust on it, way up here in the Minnesota!) I'll just keep refilling it until then. It doesn't go down too fast.

Mike
 
Nov 6, 2006
9,884
Hunter 34 Mandeville Louisiana
Best case is a really bad seal between the heat exchanger bundle and the tank. A big o-ring on each end .. easy to accesss.. pull the covers and they are there..(Page 104 in your manual link, part #5, Yanmar 24311-000700) ya need two.. the other gaskets for the cover are part # 128695-44070 two of those too.. (they would not cause this problem but will need to be changed) .. Worst case .. The tube bundle has corroded through and will need to be either rebuilt or replaced; part # 128290-44400.. Hold your breath when you check the price of that part! There may be some aftermarket folks who can provide one at a better price; I don't recall who they were.
The line leaving the cap on engine aft is seawater leaving the heat exchanger.. It goes to an anti-siphon loop on the back there before going into the mixing elbow to cool the exhaust.. The little thing on top is a spring loaded valve to break any siphoning that might get sea water into the engine
EDIT You Tube of working the heatex: He never pulls the tube bundle, but it just slides out.
 
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Jun 1, 2016
156
Hunter 28.5 Lake City, MN
Claude,
Thanks for the input, that was really helpful. In looking at what's facing me, the biggest problem I'm going to have is to get access to the engine. I can remove the front cover (lower part of the stairs) and there is an access panel on the port side, about 10 x 14 inches), but there is a board on the back that doesn't allow access to the exhaust and the back of the heat exchanger. I'm going to have to see if I can find a way to remove that panel to that I can get easier access to the rear bolts on the engine.

You're right, the price of the tube bundle does take your breath away!

My biggest fear is not being able to find the actual leak, once I start taking things apart, but I'll have to see what happens.
Again, Thanks.

Mike
 

SG

.
Feb 11, 2017
1,670
J/Boat J/160 Annapolis
Before you spring for a new heat exchanger, wouldn't it make sense to plug-up the "fresh water" (anti-freeze) loop in and out, then do the pressure check?

Then you can more likely be confident that coolant is being lost in the heat exchanger. It's possible that you have an aneurysm in the tubes between the antifreeze and the raw water where the coolant is leaking. It's possible that it's the seals at each end (I don't know what yours size Yanmar looks like).

I just replaced a heat exchanger bundle on our Yanmar 4JH2-DTBE - I recall there was only one left in the U.S. and it was over $700 for the parts and shipping. The full exhanger assembly is a multiple of that and has to "come from Japan".
 
Oct 22, 2014
352
Pearson P303 #221 RockPort Maine
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SirMichael Just did mine last year 2GMF same thing. 1. I found fluid coming out my heat exchanger bottom. Antifreeze does go to your hot water heat exchanger too. 2. Buy a cheap GUN 22. cleaning kit from wally's and use brass bristled cleaner to clear the tubes. then use the swabs and dip into CLR and rifle each tub. Don't worry about CLR or cleaning the back end just do the front. when your done and start the motor the water will flush out any left over CLR and crud. to eliminate the hot water tank just loopback hose on engine. There are 2 hoses to hot water exchanger. Call me if you like 603 312 5216. you don't have to take but the off of the Yanmar exchanger but to remove you need both ends off. Capt. Rob

All things said, I would start from the outlet exhaust to the elbow inspect and clean elbow, remove clean hose to the elbow from back side of heat-exchanger cap..etc. However, Make sure to replace ALL gaskets with NEW ones though. Hope this helps! You could have just bad gaskets too.
 

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SG

.
Feb 11, 2017
1,670
J/Boat J/160 Annapolis
Better to send it to a radiator shop and ultrasonically clean it. There is a coating that you can't reasonably remove with the routing out method.
 
Oct 22, 2014
352
Pearson P303 #221 RockPort Maine
This first picture shows a shutoff valve to prevent raw water going to the elbow until engine starts and is running for 20-30 sec. What I found was the water will backup elbow if the engine does not fire quickly enough. So knowing the engine is protected anyway with antifreeze why not eliminate water all together till the engine is started! So if my motor needs more cranking no problemo' shut the valve closed.

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More photo's
 
Jun 1, 2016
156
Hunter 28.5 Lake City, MN
Capt Rob,

Thanks a lot for the pictures and the explanation, that does put my mind at ease. I will probably give you a call sometime later today. I'm beginning to understand from those pictures just how the gaskets are laid out with the tubes.

I did figure to replace all the gaskets and in all likelihood the thermostat, just for maintenance. I had figured on bypassing the water heater output as you suggested. Considering the color of the antifreeze in the engine, I am also planning on trying to clean out the engine block with some radiator cleaner. As I mentioned, we really don't use the hot water heater. I already have the AC disconnected and the water input valve shut off.

I think I understand the shutoff valve you added, but would hope it's not necessary.

SG suggested taking the tubes to a radiator shop to have it cleaned out. I got to talking with a friend yesterday and we were discussing that we don't think there are radiator shops around here anymore, not like what they're used to be. I'm assuming that once you get the front and rear in caps off and pulled O-rings, that the tube assembly just slides out the front.

Again, my thanks for your help!
Mike
 
Oct 22, 2014
352
Pearson P303 #221 RockPort Maine
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Stargazer II installs fresh water engine flusher. By adding this I am able to flush out all salt waters out of the exchanger by allowing the boats fresh water tank to supply water to the RWPump. However, This also allows me to winterize all systems at the same time too! Even could add white vinegar to the mix too. At the end of a trip, before I shut down the engine I shut down salt water flow and open fresh water flow to flush salt out before turning off engine. This I believe is a good thing. Cost to make parts aprox. $20.00 Capt. Rob
Valves are GAS from Home Depot.
 
Jun 1, 2016
156
Hunter 28.5 Lake City, MN
Capt Rob,

I noticed the crack in the picture your exhaust elbow from your last picture.
Did you replace it?

Mike