Diesel Fuel in Crankcase on Yanmar 2GM

[belizesailor]

Not on the same engine, but had a hair line crack in an inection pump once that caused a similar problem. It was invisible to the unaided eye...even took the diesel lab some effort to finally find it.

Warning: that much diesel fulling your crankcase could create a runaway state...not good.

[Rorzech]

I don't follow your temperatures. Isn't 25 F below freezing and 15 C is only about 60 F (10 degrees below room temperature). 15 F is way below freezing. I'm sure these are just typo's ,so could you go over them again for us please & thank you.
I always thought diesels run better when they run hot. Is that the same for marine diesels ?

[HTBaggett]

Thanks to all for your comments. I have several new possibilities to check on, based on your input. Won't get back to the boat for a week or so, but will post my findings afterwards.

Again, Thank You.

[wannacat]

After changing the oil, how long before you notice this? Do you have to run the motor for it to happen or does it happen after just sitting?

[Matsubob]

If fuel is overflowing the crankcase the engine should NOT Be run again until the oil has been completely drained, refilled and a new oil filter installed. The 2GM only uses a little more than a quart of oil, so if fuel is running out of there, the ratio of diesel to oil is totally crazy. Running it that way will dilute the oil on the rod inserts and mains so badly that they will seize!
With that much diesel flowing into the crankcase I would be suspicious of the fuel pump or the injector pump. The fuel pump is the easiest to check and replace. If that isn't the problem, the injector pump would be the likely culprit. The injector pump is where fuel is being drawn into it and pumped up to high pressure. When I rebuilt mine, I was amazed at just what stands between the fuel system and the lubrication system. The fuel injector is mounted on top of the front case, where the oil pump and oil filter are also driven, at the bottom right. The oil pump sprays oil over the front end of the crank, where the governor rides, as well as the cam gears and the bottom end of the fuel injector pump, as well as pushing oil through the pipes and galleys cast into the block.
A quick (!?) removel of the injector pump would prove whether this is the culprit or not, because if it is leaking, there will be fuel all along the bottom of the injector pump, where only engine oil should be, inside the front case.
The trick is removing the injector pump from the front case. The control lever of the injector pump must be in the correct position in order for it to clear the small gap in the lip of the front cover molding. If it is too far forward or back, it will catch on the lip and not come out. (I don't know how many hours I've wasted because of this "design freak"!) But if this pump is removed after the engine has been run, even briefly, a simple sight inspection will prove whether it is the culprit, because if there is diesel leaking through it, the normal lubricating oil will be so diluted that there will be liquid dripping off of the bottom of the pump! Diesel! If not, then, reinstall it and look elsewhere.
Reinstalling it means that the above mentioned pin on the control shaft in the injector pump must be inserted through the gap in the front case, and engaged with the vertical fork that goes to the governor assembly. If it isn't engaged in that fork, either wide open throttle will occur (wrong side of the fork and not engaged) or it may not even start (other side of the fork and not engaged) In either event, removing the injector pump to remedy the situation will be a hassle because that pin must be positioned where the gap in the front cover is, or it won't come out, no matter what is done! (the only workable method I have found is to remove the front case)
And don't ask what it feels like to frantically run for the fuel shutoff at the tank with the engine screaming at Wide Open Throttle, because that is the only way to kill the engine.
If, however, it is determined that it is leaking diesel fuel, a quick teardown and inspection/reassembly should do the trick. As long as no adjustments are touched, and only the mechanical parts are removed, cleaned and reinstalled, though it is tedious, it is all straightforward. Downloading a Yanmar shop manual will help immensely at this point! These pumps are so finely machined that even the smallest particle can cause malfuntion or leakage, but a thorough cleaning should do the job.

[Wotname]

Originally Posted by Rorzech

I don't follow your temperatures. Isn't 25 F below freezing and 15 C is only about 60 F (10 degrees below room temperature). 15 F is way below freezing. I'm sure these are just typo's ,so could you go over them again for us please & thank you.
I always thought diesels run better when they run hot. Is that the same for marine diesels ?

This should make it clearer for you

Originally Posted by Alan Mighty

.........
It should be easy to pull the old thermostat. It should (? I hate making assumptions) have its opening temperature stamped on it. It's then easy to put water in a saucepan, suspend the thermostat by wire so it is not in contact with the sides of your saucepan, and bring the water temp up to about 25F (15C) above whatever is stamped on the thermostat.

The theromstat should be open at that temp.

.......

[HTBaggett]

Originally Posted by wannacat

After changing the oil, how long before you notice this? Do you have to run the motor for it to happen or does it happen after just sitting?

It took awhile to show up by running on and off for a week. Don't think anything is happening while sitting.

[HOPKINS]

Originally Posted by HTBaggett

It took awhile to show up by running on and off for a week. Don't think anything is happening while sitting.

on some yanmars it took about 6 hrs of cruising before the crank case was full , others over a period of 4 days , probably a pin hole in this one , they make some pretty good electric 12 volt pumps these days , i had one lasted 12 years , as long as filters were changed regular . if your fuel tank is higher than your motor , if the hole in the seal is big enough fuel will pass.