fuel is leaking into my lube oil

[Mystic51]

My Yanmar 3GM engine only has 142 hours on it. The engine started knocking and blowing smoke yesterday so I got a tow. We checked a number of things and when I pulled the oil dip stick oil gushed out and is very thin. The next day we pumped out over seven qts.; should have been less than three! It is thin and most certainly has diesel fuel in it. My mechanic thinks a faulty injector pump or a bad injector though he said these are rare occurrences and he seems unsure. I am on a freshwater lake without much of choice in mechanics. Any thoughts as the source of my problem?

 

[RichH]

99.99% chance its a ruptured diaphragm in the LIFT pump.

Been using any so-called Bio-diesel or diesel fuel made from reclaimed 'cooking or edible oil'????
Many of these "green" 'eco-wonders' are incompatible with most of the polymers (seals, diaphragms, gaskets, etc. etc.) found in older diesel engines. Especially in the eco-wacko areas of the country where the price of fuel is artificially obscene, many times 'the mob' and other illicit entities distribute 'real' diesel fuel adulterated with 'these 'reclaimed' oils, etc.

 

[Mystic51]

We have owned boat since August of last year. Don't know what the former owner used for fuel but he is an experienced sailor. The boat came from a different lake. We buy our diesel from a marina. Is the pump hard to work on?

 

[Mystic51]

another question. I thought the lift pump was the little pump in line before the fuel filter. What about the injector pump?

 

[Steve Dion]

The lift pump is on the starboard side of motor. Depending on the model of your boat, it may or may not be easy to access. It is right near the dip stick.

What model boat do you have? If you have a manual, you should be able to get some idea of how to remove it.

 

[Alan]

RichH is almost certainly right. The lift fuel pump is the most likely culprit. A diaphragm split will dump fuel into the crankcase. Replacement of the pump is relatively easy.
I would STRONGLY advise you NOT use that "mechanic" given his lack of knowledge.

BTW make sure to replace the oil filter also.

 

[Mystic51]

I got almost the same answer from other sources that it is likely the fuel lift pump. seeing that they are reasonably priced and relatively easy to install i have one ordered that should arrive tomorrow. Another piece of evidence is that the level of contaminated oil in the crank case rose significantly overnight without me running the engine. the tank is mounted high so gravity still moves the fuel. Hope to be on the water for the 4th.

thanks

 

[RichH]

I got almost the same answer from other sources that it is likely the fuel lift pump. seeing that they are reasonably priced and relatively easy to install i have one ordered that should arrive tomorrow. Another piece of evidence is that the level of contaminated oil in the crank case rose significantly overnight without me running the engine. the tank is mounted high so gravity still moves the fuel. Hope to be on the water for the 4th.

thanks

This may be too late as you may have already ordered the part ....
Seek a diaphragm for the lift pump that is made from EthylenePropyleneDiamineMonomer - EPDM, as this rubber compound is more resistant to attack by the 'newer' bio-fuels and 'blends' especially those that have a high % of 'reclaimed' edible oils. The old standby Neoprene or Buna isnt very compatible with the 'newer' fuels.

 

[Mystic51]

Yes it is too late for the pump was ordered and installed yesterday. We will determine today if any fuel is still getting in the crankcase. I did discover that in Southern Illinois where the boat came from that bio diesel is what most stations carry and I am sure that he was filling the boat from a plastic can for the marina up there might not have a diesel pump. Our marina at Stockton lake, MO does not cell bio and no one here has ever had a similar fuel problem from what I can tell. We are pumping out all old fuel and replacing all filters. thanks for the help!

 

[Mystic51]

The boat is fixed. The lift pump was replaced. The raycor and fuel filters (very clogged with varnish like sludge) have been cleaned and replaced, the fuel tank has been pumped of all bad fuel, and fuel lines were inspected for damage. The engine runs like a champ and fuel is no longer leaking into the crankcase. Lesson learned; beware of bad diesel and most likely biodiesel. I discovered that Illinois is the no. 1 consumer of biodiesel in the nation and the boat came from southern Illinois.

 

[RichH]

Mystic -
The easiest way to rupture and 'fatigue' a lift pump diaphragm is to use a filter with LESS/SMALLER retention rating that the 'OEM design'.

As an example, a 2µM rated filter will typically have 5 TIMES the 'pressure drop' across it as a 10µM rated filter for the same exact flow rate ... and the lift pump will then have to pump at this higher pressure (vacuum) to maintain the same flow demand of the engine.
So the moral of the message is: If you somehow come to the (erroneous) conclusion that a smaller retention filter is somehow 'better', you MUST increase the surface area of the smaller retention filter ... so to keep the 'load' on the lift pump the same as when you were running the larger µM rated filter. If you dont increase the surface area, the smaller µM filter will more quickly plug (at more than 5X the rate of the larger µM filter ... when changing a 10µM to a 2µM), the motive pressure (vacuum) requirements will INCREASE .... and you WILL increasingly risk to eventually rupture the lift pump diaphragm.

 

[tsmwebb]

Mystic -
The easiest way to rupture and 'fatigue' a lift pump diaphragm is to use a filter with LESS/SMALLER retention rating that the 'OEM design'.

I know you feel very strongly about this. But, I'm wondering if you have any evidence that lift pumps are actually being damaged by small retention rated filters. The only filter on my diesel engines that is part of the "OEM design" is on the pressure side of the pump... AFIK, there is no OEM designed, or even officially recommended vacuum side filter for a 2gm20. IME, the 2u Racors that were installed by the Yanmar dealer when the boat was constructed have worked just fine. I've got 2 of them and both of their lift pumps are fine after almost 1700 hours... And, I haven't heard any other reports of problems either...

--Tom.