oil dilution with diesel - SailNet Community
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post #1 of 21 Old 04-14-2010 Thread Starter
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oil dilution with diesel

Have a perekins 4-108, runs perfect, but have some diesel infiltration in my oil, does anybody have ideas. please. Motor has been rebuilt 100 hours ago.
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post #2 of 21 Old 04-14-2010
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You can get diesel contamination from the injectors/seats or from the seal on the injection pump going bad. Not sure how you determine where it is coming from, maybe someone with experience on your engine will know.

John
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1988 Brewer 40 Pilothouse

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post #3 of 21 Old 04-14-2010
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One other place to mention is the lift pump if it is a cam driven one. It has been too long since I worked on a 4108 so I can't really remember how it is setup.
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post #4 of 21 Old 04-14-2010
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A common problem is a failed diaphram in your lift pump which will also cause air locking in the injector system due to air being drawn in through the failure. This likely won't happen if the fuel supply is higher than the injector pump, but will cause lube oil dilution. Try disconnecting the supply line from the supply tank and pressurise the line with an air pig and check for leakage.

Hope this helps,

Cheers, Dumah, Halifax, NS

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post #5 of 21 Old 04-14-2010
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Go for the diaphragm in the mechanical fuel pump first, this is a common failure point on this type of engine. I had it happen on a Perkins 4.203 and will never forget how much it cost me to find out!!!!
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post #6 of 21 Old 04-15-2010
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Not only is this bad for the motor since the lubricity is not as good, it's dangerous. If you get enough diesel in the crank case you can end up with a runaway motor - it will start running at max rpm from the diesel. The only way to shut it off is to block off the air or shoot a fire extinguisher into the air intake. If you have to do this use a CO2 type if you can!
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post #7 of 21 Old 04-15-2010
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Won't argue the runaway engine, we still dilute crankcase oil up north in order to be able to start it, the lighter elements evaporate off as the engine warms up, in addition I've been known to use fuel oil for coolant in an old D8 with a cracked block (do NOT remove rad cap from hot engine) and saved the machine for that season.

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post #8 of 21 Old 05-04-2010
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Quote:
Originally Posted by SteveInMD View Post
Not only is this bad for the motor since the lubricity is not as good, it's dangerous. If you get enough diesel in the crank case you can end up with a runaway motor - it will start running at max rpm from the diesel. The only way to shut it off is to block off the air or shoot a fire extinguisher into the air intake. If you have to do this use a CO2 type if you can!
Now thats a new one on me !
This should be the 10th post or so so IŽll be out of your hair soon.

Question : how does the diesel in the sump get into the combustion chamber?
The compression is 16 to 20 to 1 past the rings so that route is therefore unlikely .
Its a fanciful story but not true I am afraid
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post #9 of 21 Old 05-04-2010
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Probably a failing diaphragm in the engine's lift pump.

To verify: remove the pump from the block, reinstall the fuel lines and hand pump the pumps cam follower (lever); some pumps have manual levers on the external side to help bleed the system, if so use the manual external lever. Pump the lever until the system is fully pressurized .... and look for fuel leakage from the backside of the pump (where the cam follower (lever) is.
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post #10 of 21 Old 05-04-2010
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Quote:
Originally Posted by tytower View Post
Now thats a new one on me !
This should be the 10th post or so so IŽll be out of your hair soon.

Question : how does the diesel in the sump get into the combustion chamber?
The compression is 16 to 20 to 1 past the rings so that route is therefore unlikely .
Its a fanciful story but not true I am afraid
With over 35 years in the industry, I can testify that a runaway engine is not only possible but highly likely. It is not the liquid in the sump you worry about, it is the fumes drawn in via the manifold due to crankcase ventilation systems. Crankcase ventilation systems "recycle" blowby and other vapours from the sump to the intake where they are burned reducing emissions to atmosphere. A runaway engine is a very dangerous thing, ALL diesels have a governer of some kind in order to keep the engine from self destructing. When the engine runs away, it is no longer in control............PERIOD and catastrophic failure is the eventual end, usually in thrown bits and parts and often explosions. Be afraid, I am.

Cheers Dumah,
Halifax, NS

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