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Old 13-07-2017, 21:40   #1
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Diesel Fuel in Crankcase on Yanmar 2GM

I've been chasing this issue for awhile now, following the recommendations of a professional marine service. We started with replacing the Main Fuel Lift Pump, then rebuilt the head along with checking the injectors that had been replaced new a few years back. Finally we had the Injector Pump rebuilt, professionally. Runs great but Diesel Fuel, after running it, will eventually fill up the crankcase and flows out of the dipstick hole.

Does anyone have an idea what could be causing this?
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Old 13-07-2017, 22:06   #2
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Re: Diesel Fuel in Crankcase on Yanmar 2GM

If you have replaced the injectors, that more or less eliminates fuel leaks from them. You've checked that the fuel return line is not blocked?

Do you have temperature gauge on the engine? Or a handheld infra-red thermometer? What temperature is it holding when running?

The engine is raw water cooled or freshwater cooled? I'm guessing it should have a thermostat set to open at an engine temp of about 60 Celsius. Have you checked the operation of that thermostat?

At what speed are you running the engine? High enough to get the engine to operating temp? What is your sea surface temp?

Do you keep fuel consumption records? Do they show a change in fuel consumption at a certain time?

I ask those questions because, if you've eliminated leaks from the injectors, then the next easy hypothesis is that the engine is running too cold. And fuel is therefore not being burned and is leaking past the piston rings to the crankcase.

The thermostat/temperature switch might be stuck open, meaning that the engine is not getting up to temperature.

I'm not saying that the temperature hypothesis is definite. But pulling the thermostat and testing it is inexpensive and possibly easy. And doing it would eliminate one possibility.
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Old 13-07-2017, 22:11   #3
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Re: Diesel Fuel in Crankcase on Yanmar 2GM

Don't know the engine, but the usual causes are places the have fuel and oil in common. Probably most common is the seal on the injector pump. Just because the pump was rebuilt doesn't mean there isn't an underlying problem damaging the seal. Many times the shaft will get worn or pitted where the seal rubs and so a new seal is too loose or damaged right away. Also, the pump housing could have a hairline crack.
Fuel coming from an injector usually creates heavy black exhaust smoke because it's so rich.
I've probably seen 50 injector pump seal leaks for every lift pump leak.
The problem isn't in the head unless there are internal fuel lines that can crack. Not very common. With enough fuel to flow out of the dipstick, it has to be pressurized fuel, probably from the injector pump.
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Old 13-07-2017, 22:25   #4
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Re: Diesel Fuel in Crankcase on Yanmar 2GM

Thanks Alan for the quick reply.

The following are my responses to your questions:

You've checked that the fuel return line is not blocked? No, but will.

Do you have temperature gauge on the engine? No

Or a handheld infra-red thermometer? Yes

What temperature is it holding when running? Have not checked, but will.

The engine is raw water cooled or freshwater cooled? Raw

Have you checked the operation of that thermostat? No, but have s new one but have not installed it yet, but will.

At what speed are you running the engine? High enough to get the engine to operating temp? I've run it at various speeds and loads.

What is your sea surface temp? In Florida so it near 80 F

Do you keep fuel consumption records? No

Do they show a change in fuel consumption at a certain time? No
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Old 13-07-2017, 22:41   #5
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Re: Diesel Fuel in Crankcase on Yanmar 2GM

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Originally Posted by HTBaggett View Post
Or a handheld infra-red thermometer? Yes

What temperature is it holding when running? Have not checked, but will.
You obviously need to cure this problem before you suffer bearing damage (if fuel is overflowing from your dipstick, there's enough fuel to dilute the lubricating oil so it is not doing its job).

So although I am tempted to ask you to take the boat for a solid run at a high engine speed (such as 2900 rpm) and then measure the temperature at the top of the thermostat housing, at the heat exchanger, etc, I'm loath to do so because of the risk of bearing damage.

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.

Then add cool water (or just be patient and let the water cool) until it is at least 10F (about 5 or 6C) below that temp stamped on the thermostat. At that temp, a healthy thermostat should be closed.


Quote:
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Have you checked the operation of that thermostat? No, but have s new one but have not installed it yet, but will.
I'd argue for you testing the old thermostat first. If it tests okay, then I've wasted your time. And then another opinion is needed.

If the old thermostat fails the saucepan test, then you're all set to replace it (did you get a new gasket with the new thermostat? I'm unsure whether you should have one).

And then change the oil.
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Old 13-07-2017, 22:56   #6
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Re: Diesel Fuel in Crankcase on Yanmar 2GM

On that small Yanmar 2 GM (or other diesels) the most common source of diesel in the oil(apart from injector being bad) would be leaking from the lift pump it self into the motor or from the injector pump it self from a bad seal, both the lift pump and the injector pump have access to the oil and both rely on seals,

I know you state they have been serviced , but thats when i find most issues crop up as it's easy to install a seal badly or have seen cases where the seal was mistakenly installed up side down,

Some engine have internal bleed/return lines with in the rocker cover and can leak from there but believe the 2 GM from memory does not!

There fore would be looking at either the lift pump or injector pump
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Old 13-07-2017, 23:22   #7
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Re: Diesel Fuel in Crankcase on Yanmar 2GM

Further to my earlier input,I note you said the injectors were replaced several years back, in several years injectors could go bad, so the question being is: Has this issue been continuing through out the years, with no success at all?.

I dont see any connection with a thermo stat issue at all, running hot or cold wont cause this type of fuel getting into the oil
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Old 14-07-2017, 09:59   #8
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Re: Diesel Fuel in Crankcase on Yanmar 2GM

your lucky the engine didn't run away


from my experience, the injector seats are leaking


you may have damaged bearings
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Old 14-07-2017, 10:46   #9
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Re: Diesel Fuel in Crankcase on Yanmar 2GM

I think I would look again at the fuel lift pump and injector pump installation and seal,
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Old 14-07-2017, 13:03   #10
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Re: Diesel Fuel in Crankcase on Yanmar 2GM

I had a similar problem on my 3GM. It turned out to be a leak in the diaphragm of the lift pump. A few dollar part prevented hundreds in damage.

Just replace the lift pump - easy, cheap and if that isn't the problem, you have a spare.
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Old 14-07-2017, 13:33   #11
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Re: Diesel Fuel in Crankcase on Yanmar 2GM

check your lift pump.
busted lift pump will send fuel into your oil.
rebuild or replace it and buy a spare.
should be first thing checked if your mechanic has brains. oops sorry. cheapest first then more dough as ye hook the victim in. not most dough first. they will stop using you.
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Old 14-07-2017, 14:50   #12
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Re: Diesel Fuel in Crankcase on Yanmar 2GM

Use Volkswagen type electric fuel pumps that are now made for diesel (about $55) even though I use the ones for gasoline ones (used to cost $15) for over 25 years without a problem. I have two installed, one at tank level (in the bilge) and the second just before the primary filter and water separator level with the injector pump. I carry a couple spares and have wired and plumbed them to be relatively "quick" change.

The problem with most small marine engines is that are adaptations of non-marine engines designed for small tractors, pumps, forklifts, etc. and they use the power takeoff, which has direct access to the crank case, to drive the mechanical fuel pump and sometimes even the raw water pump as well. Guaranteed problems. I pitched the whole thing (fuel and water pumps) installed the electric fuel pumps, had machinist turn an additional crank shaft pulley to install in front of the original one and installed a belt driven Jabsco raw water pump. Damn, had to replaced one Jabsco and one electric fuel pump in since 1991.
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Old 14-07-2017, 17:14   #13
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Re: Diesel Fuel in Crankcase on Yanmar 2GM

Maybe?
Maybe this problem happens when the boat is sitting for some time (months?) and you are changing the 'diesel' before you go for a trip but then the sump fills up again while sitting again?
Or?
Or are you saying it fills up the sump while you are underway?
Height of fuel tank compared to height of injectors?
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Old 14-07-2017, 17:32   #14
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Re: Diesel Fuel in Crankcase on Yanmar 2GM

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Originally Posted by boeing1 View Post
I think I would look again at the fuel lift pump and injector pump installation and seal,
BINGO!
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Old 14-07-2017, 17:44   #15
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Re: Diesel Fuel in Crankcase on Yanmar 2GM

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Originally Posted by HTBaggett View Post
I've been chasing this issue for awhile now, following the recommendations of a professional marine service. We started with replacing the Main Fuel Lift Pump, then rebuilt the head along with checking the injectors that had been replaced new a few years back. Finally we had the Injector Pump rebuilt, professionally. Runs great but Diesel Fuel, after running it, will eventually fill up the crankcase and flows out of the dipstick hole.

Does anyone have an idea what could be causing this?
yes, i was a mechanic for Moorings and TMM for two years , this is a common problem with Yanmars in 99% of the time it was the seal in the fuel pump, it can even happen on a new pump out of the box, starts with a pin hole , due to inferior or old seal material , you might get one that has been on the shelve for a while , or siting in the sun , heat breaks down the material.yes it could be the seal in the front of the injection pump , but i worked on over 40 different boats and motors , this is kinda rare.
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