Runaway Yanmar 1GM

[Chief Engineer]

Customer came up to me in a panic.

"I took the boat out....about 10 minutes after starting the engine and underway there was a BIG cloud of white smoke, the engine really revved up and a lotta goo blew out the back" "I shut the engine down...waited awhile, restarted and came back"

I went to the boat....the engine started OK, no noise out of the norm, linkage OK. Checked oil. (Engine has less than 100 hours on it.)

Oil level was 1" plus above full mark.............................................. ..

[captden]

I had the same thing happen on my last boat, talk about scaring the sh** out of me. It was a Yanmar 4jhe, I had just finished running the engine for about 2hrs charging the batteries at about 1500 rpm and everything seemed normal, when I throttled the engine back to idle I had the oil pressure alarm go off something that never happened before. So I brought the throttle back up to see if the alarm would stop the rpms shot up and it started smokeing like crazy and sounded like it was going to tear itself apart.

I pulled the shut off lever and nothing happened just kept running at full power. As I stood there in shock in what seemed like forever trying to figure out what to do next, this think just kept running away. Now I run down below and open up the door to the engine room and of course it sounded even worse than in the cockpit
.
Now for the good part, here I am thinking how the heck am I going to stop this thing before it self destructs, I'm scared to even go in this very confined space to do something as I'm thinking if this thing comes apart with me inside it's going to take me out with it. I'd say now it seemed like this thing was running for an enternity even though it was probably just 45 seconds, I grab an orange that was on the table thinking if I pull the air cleaner off I can jam the orange into the air intake and try to stop air flow cuz a diesel just needs air and fuel to run and I already stopped the fuel flow when I pulled the kill lever.

I grab the air filter and give it a yank off it comes I go flying back because it come off a lot eaiser than I thought (or I had super strength) and when it came off oil came shooting out of the intake and the engine stops.

After a couple of stiff drinks I went to bed, I'll deal with this in the morning.

What I found in the morning was the same as you, the oil level was a lot higher that it should of been and when I drained the oil it was very thin and had a strong diesel smell. To cut this short it turned out I had two bad injecters pouring so much fuel that the excess was some how going into the oil and when I throttled up the engine there was so much back pressure it was feeding oil into the intake and the engine was running on this.

After replacing all the injectors and doing an oil change the engine ran like a champ. Now I learned two things, my new boat has a generator to charge batteries and diesel engines are tough and can take a lot punishment.

Funny now but I bet it took a couple of years off my life that night
Captden

[delmarrey]

Some diesels have a butterfly valve on their intake just for this reason.

Once I get my new Yanmar installed, I guess I'll be keeping a hard rubber ball in my motor compartment to shove in the intake tube, if need be.

Another reason to do pre-underway or hourly inspections. Then I find this on the air intake. Lets hope the motor starts up right away each time and I get the wetlift/exhaust installed perfectly.