Yanmar Diesel stalls when underway

[gkeiser]

Hi, I have a Yanmar 1GM diesel that runs well at high rpm when stationary (and when in gear) at the dock and cooling water exits the exhaust. However, when I am underway at higher rpm the exhaust outlet sits under the water and the engine slowly dies out. And now, unfortunately it won't start. I had recently ran the engine underway, but noticed that it was dieing out at higher rpm so I backed it off, and it ran fine for 40 mins. The engine has been recently serviced for air in my fuel line from a unrelated issue (I ran my fuel tank empty) and had my oil line pinhole leak as well. This time however, the engine won't start now. I noticed that there is not a loop between my muffler and the transom, and the muffler sits below the waterline. The muffler sits below the exhaust elbow. I'm concerned that sea water is backing into my muffler and blocking the exhaust and cooling water from exiting the exhaust outlet when I'm underway (and possibly flooding my engine?!). I didn't have time to try emptying the muffler to see if that would solve the problem, but I am interested to see if anyone would think this could be an issue? It is an O'Day 25 1983 which was equipped with the Yanmar 1GM.

Thank you.
Geoff

 

[kloudie1]

My first guess would be a plugged fuel tank vent line.. that would allow the engine to run fine for a while then slowly die as the tank built a vacuum and fuel flow stopped. You can test for this by opening the fuel fill cap and running the engine under load, being careful to not let any water get into the filler. My second guess would be a plugged fuel line/filter.. There may bbe a small wire gauze over the tip of the fuel pickup tube inside the tank. It would not be uncommon to have a little sludge plug the gauze and stall the engine when it needs more fuel than it uses at idle. A plugged fuel filter would allow the engine to run at idle and lower power until it dies. After it dies from a plugged filter, the fiilter may not let more fuel throuugh and prevent it from starting..

 

[gkeiser]

@kloudie1 Thank you for the information, I will put that on my list of things to check. My mechanic had also run the engine at high rpm, in gear, pulling at the bow lines with no issues. I also have done the same thing since experiencing decreased engine power when underway. This has made me think it's water getting back filled into the muffler/waterlock/silencer and filling it up to the point that the engine stalls when I am underway, since the exhaust outlet goes below the waterline. Do you think this is at all possible?

 

[Davidasailor26]

I think it’s unlikely that the back pressure could stop the running engine, although once the engine is stopped if there’s no loop you could get a siphon and water lock the cylinder. I think the more likely reason for the engine stopping while underway is some kind of gunk in the tank getting stirred up and onto either the pickup tube or the filters. That could explain why it happens when the boat is rolling in a seaway and not at the dock.

 

[Ralph Johnstone]

I noticed that there is not a loop between my muffler and the transom, and the muffler sits below the waterline.

This arrangement is not, in itself likely to be the cause of your problem but may I suggest you replace your exhaust line with a loop in place before you blow the head off your engine ? I cannot see how this arrangement can exist unless your exhaust port is way above the waterline. If the port is close to the waterline and submerges when you're sailing because of squat, it's only a matter of time before all hell breaks loose.

Has your mixing elbow been checked recently ? Blockage may be causing problems.

 

[kappykaplan]

Has your mixing elbow been checked recently ? Blockage may be causing problems.

 

[dlochner]

Clogged fuel filters
Clogged fuel lines
Air leak in the fuel line

 

[gkeiser]

Hi all. An update here. My exhaust hose has a loop and mufler was not backed up with water. I found my fuel tank vent was completely clogged and my fuel system filled with some air. I bleeded the fuel system and the engine started back up! Unfortunately I found that one of the oil lines which runs under the engine was so corroded that it developed a hole, and oil was flowing out when the motor was running. A low oil pressure indicator when off and the engine stopped. I had the oil line replaced and the engine runs better now, however, it won't run for more than a couple mins. No overheating, no air in the fuel system, and no oil pressure issue. I suspect the injector now. This engine was left for many years unattended, so I'm not surprised I've encountered so many issues. Thanks for your help!

 

[Ralph Johnstone]

I noticed that there is not a loop between my muffler and the transom

My exhaust hose has a loop

Are you sure ? ? ? ? ? What does this loop look like ?

however, it won't run for more than a couple mins. No overheating, no air in the fuel system, and no oil pressure issue. I suspect the injector now.

The injector and other such costly items are always the LAST things you check not the first.

I had the oil line replaced and the engine runs better now, however, it won't run for more than a couple mins.

Your injector will not cause your engine to stop. Smoke badly and lack power but not stop. Keep looking.

 

[Benny17441]

It sounds like clogged fuel filters or globs of crap in the fuel tank. I would replace the fuel filters and connect a portable outboard tank with fresh diesel fuel and see how the engine runs. If the fuel tank is the culprit, it will need cleaning or replacing.

 

[Techstyle]

I had a similar problem and found that the screen before the first fuel filter was completely clogged. I took off the fuel line where it goes into the first filter and found no fuel coming out. the tank was higher so it should have been pouring out. I blew the line back into the tank and got a mouthful of diesel. I then got an air line and blew the content back - no more issues. I polished the fuel with an external filter and pump and treated the fuel with biocide and enzyme to break it down. That was 2 years ago, no problems since.

 

[Mark Maulden]

The fuel tank/pickup could be root of your problem. You can clean lines, screens, replace filters, etc, however, if the tank is full of crud, this can happen again. Also tank vent and hose to such..