Broken coolant line Yanmar 2GMF

[Daniel Hoffman]

A coolant line broke, the engine overheated and ran away.

I did get it to stop, but it wasn't easy. I thought it was a clogged filter at first.

Getting towed back now. I'm very worried about the engine.

[darin doherty]

That looks like the actual exhaust elbow broke off.

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[Daniel Hoffman]

The "Joint" broke. The hex part stayed with the elbow and the U-type elbow has the stub.

It looks close to be able to spin the U-Elbow on, but i think the elbow needs to come off too. I measured, and it's close.

The dipstick showed black oil a bit low, but no foamy stuff. I hope the engine survived. I'll change the oil and filter and am not confident about getting the broken part out of the U-elbow without damaging the internal threads.

Dan (the other one) 

Fourth and Goal

P 31-2

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[darin doherty]

A compression check should give you an indication of the condition of the pistons/rings and valves.

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[Daniel Hoffman]

Would you do a compression test before attempting to start the engine? I'm thinking broke is broke. But the engine did overheat and run away. 

It's hard to evaluate next steps. Buying parts or tools to do a compression test on an engine that needs major work is a tricky decision.

I'm thinking about starting it up and running it for a couple of minutes against the dock lines. It won't overheat since the anti freeze side is good.

Dan (the other one)

4th and Goal

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[Dave Cole]

How do you know it overheated? 

If that's the case, you likely have more than one problem.  A broken exhaust and something else.  The way that broke, you should have had sea water being pumped over the engine out of the broken off fitting.

Did that happen?

Was the cooling water valve open at the thru hull?

[darin doherty]

I would do a simple compression check turning the engine over by hand.  If a valve is damaged, burnt or the cylinders or rings are damaged, you can cause more damage by starting it.

If it turns smoothe and the compression seems to be ok, even in the ball park then change the oil and try starting.

Darin

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[Daniel Hoffman]

Yes, the engine had seawater pumped all over it. I'd been running the engine at about 2400 rpm and water was being pumped out of the stern the whole time, even after the speed dropped.

I thought it was the fuel (That's another story.). The engine wouldn't stop with the fuel cutoff pulled way out. That's a sign of a runaway diesel.

Steam filled the cabin and the smoke alarm went off. There was water all over the cabin sole. I don't grasp the concept of how that works because the mixing elbow is on the downstream side of the heat exchanger.

The antifreeze and engine oil looks good.

Dan

Fourth and Goal

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[Daniel Hoffman]

Thanks. 

I'm thinking damaged cylinders or rings are game over for the engine. Wouldn't it be easier to just replace than have repaired?

Dan

Fourth and Goal

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[darin doherty]

It is probably a lot easier to replace but a lot more expensive.  Depends on the extent of damage.

Runaway diesel is usually from the diesel buring the oil on the compression stroke once the fuel is gone.  Are you sure the fuel shutoff could not be leaking by ?  For a runaway diesel, IIRC, the engine has to be really hot to burn the oil, and there needs to be enough oil leaking into the cylinders to do that.

How did you get it to shut off.  For a runaway diesel,  I believe you need to stop the air flow by blocking the air inlet and choking it out.

Darin

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[Jeff Griglack]

There is a plumbing wrench/tool that fits inside the pipe to unscrew a broken pipe like that. You might be able to find one that large online or at a plumbing supply store.

------------------------------------------------------------------
| Jeff Griglack             "Jabberwocky" P-365 #269

------------------------------------------------------------------
| "Don't take life so serious, son, it ain't nohow permanent"
|                   - Walt Kelly
| 'Years ago my mother used to say to me, she'd say, "In this
| world, Elwood, you must be" – she always called me Elwood –
| "In this world, Elwood, you must be oh so smart or oh so pleasant."
| Well, for years I was smart. I recommend pleasant. You may quote me.'
|               —James Stewart as Elwood P. Dowd
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[Dave Cole]

Id repair the exhaust and fire it up.  Make sure the oil is clean and the antifreeze full.  

Be prepared to block off the air intake to kill the engine.  Diesel smoke, water splashing all over the place will make a mess.  

If your engine was starting ok, chances are the compression is ok.  

Engines are serious $$.  New or rebuilt. 

Dave

10M #26

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[darin doherty]

The do make internal pipe wrenches, but depending on how hard it is you can take the elbow to a weld shop and they can weld a bead on the inside of what is left of the fitting.  This will cause the  fitting to shrink and you should be able to get it out.,  The welder can even weld some tabs to the fitting to get a wrench/bar etc to turn it out.

Internal pipe wrenches that size are about 90.  

If you are careful with a die grinder and a burr, that is another way.

Good luck.

Darin

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[Daniel Hoffman]

Thank you, Dave, that's my thought, except I'll also change the impeller too. 

My temp indicator never alerted me and that's concerning too. It's a smaller issue, but dependability is nice.

Pulling the hoses off now...

Dan

Fourth and Goal

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[Daniel Hoffman]

I've done the sawzall blade on a handle and chisel trick with success in the past. It's risky.  My internal wrenches only go up to one inch, but they yave jever worked on heavily corroded fittings because they tend to expand the stub.

It's a bit of a surprise to me that this failed. Water still was pumping out astern. The concept of how this works escapes me. The cabin was filled with steam and exhaust and still stinks.

Dan

Fourth and Goal

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[Daniel Hoffman]

Actually, I'm not sure the cutoff couldn't have been leaking by. It never failed before. 

I pulled the fuel shutoff really hard and the engine stopped. Given your comments, I'm not convinced it ran away, but this was a first for me. 

This is the replacement and it might be the best way to go.

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[Last Resort]

check out the new upgraded SS version....had one for over 10 years and no issues!  And alot cheaper!!!

https://www.ebay.ca/itm/305551407808

[Daniel Hoffman]

Thanks Dave. You're asking good questions. The engine was running at about 2200 RPM and the speed was just above 6 MPH on calm seas with no wind when it suddenly slowed down, to just above stalling speed when it ran rough.

1) I assumed that it was the fuel filters because I had algae treated with Biobor JF, a diesel biocide, and Star Tron Enzyme Formula. Star Tron breaks sludge into smaller particles which the filters pick up, clogging them. The replacements are onboard already 

2) When trying to start the boat, a friend adjusted the full shut off thinking it wasn't opening. The issue was bleeding it at the injector pump because it didn't even make it to the loosened injectors. A different friend with a 2GMF20 took a 10mm wrench to bleed it at the iniector pump and it started right up.

3) I gave it more throttle.

4) Because I want to run the fuel out, I've been running the engine in the slip-- and not checking the strainer even though we can see the sea grass near the surface. The filter had a lot of grass in it when I checked it last night.

5) When the engine slowed, I saw water coming out the stern with the exhaust.

6) Then came the smoke....

7) The pipe failure may have just been a fluke of timing, or somehow related to a slower flow of seawater coolant. Perhaps the vibration at stalling speed took a corroded nipple over the edge.

Dan

Fourth and Goal

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[Daniel Hoffman]

Thanks. I have the type in the box in the upper right and not the other style of mixing elbow.

I'm going to replace the U-elbow and nipple and am not sure about the lower elbow. The plan is to put it in a vice and use a big pipe wrench. There's enough meat protruding on the broken part tondo the saw and cold chisel trick. That work and the risk to the threads and the thought that the corrosion won't let a new nipple seat properly if it needs to go a bit deeper vs the price of a new one is the balance. It's unlikely with teflon tape and pipe dope.

Dan

Fourth and Goal

On Fri, Oct 3, 2025, 7:38 AM Last Resort <lastre...@gmail.com> wrote:

check out the new upgraded SS version....had one for over 10 years and no issues!  And alot cheaper!!!

https://www.ebay.ca/itm/305551407808

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[Last Resort]

Not sure if I'm reading your reply right, so if you already have bought the U version, fine, But if not, you don't HAVE to replace the old one with the same U version.  The one in the bottom left of your picture is the newer upgraded version that does the SAME thing, and doesn't clog up like the older version.  And much easier to install.   Good Luck!!!

[Daniel Hoffman]

Thanks for the reply, "Last".

I was talking about this with my brother who has a Catalina 34 with a Universal 23, that needed both heat exchangers replaced. I was going to replace some of the parts and his take was, "What if they don't match and the nipple's thread isn't the same?" 

I decided that the aggravation wasn't worth the effort and ordered the whole assembly.

Had I seen your reply earlier, I'd have gone that route. Still, the original did make it 36 years. Getting the threads to seat in a particular orientation can be tricky and the straight connection would have avoided all that.

I'm hoping it just ran hot with reduced flow and the vibration of starving for fuel because of the fuel issues pushed a corroded nipple over the edge. If those filters look really bad from just about ten hours of running, I'm going to he looking for a proper way to dispose of most of the fuel, about 8 gallons in the tank.

Dan 

Fourth and Goal

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[Dave Cole]

Diesel is just light oil.  See if the oil recyclers will take it.  Autozone, etc.

Places where you can drop motor oil.

My marina has a waste oil tank that everyone puts their oil into.

Many auto repair shops will take it.  They oftentimes have waste oil burners for heat.

Dave

10M #26

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