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tj
tj, Mechanic
Category: Heavy Equipment
Satisfied Customers: 524
Experience:  10 years of john deere,agco,new holland,cummins
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Diesel fuel in crankcase oil. Why?

Customer Question

What is the cause of diesel fuel in crankcase oil?

Submitted: 7 years ago.
Category: Heavy Equipment
Expert:  DR.Cummins replied 7 years ago.

Can you tell me the model or your 6cyl? ie isc, isb ect or an engine serial number? There are many causes. I will help if you can supply some more engine info.

Customer: replied 7 years ago.
looking at my manual now it an older case 1986 i know its a 6 cyc cummings
Expert:  DR.Cummins replied 7 years ago.
Ok i just need a serial number or model id Cummins has many different 6 cyl engines you could check the engine data tag also.
Customer: replied 7 years ago.
does 6-590 manke sence ?
Expert:  DR.Cummins replied 7 years ago.
no Is it a big horse power engine or a little hp engine?
Customer: replied 7 years ago.
big hp motor, straight 6
Expert:  DR.Cummins replied 7 years ago.
ok so either an N14,855 or m11 , Well if you has your fuel system components checked/ rebuilt. Than there could be a fuel drain line restriction or most likely a cracked or poures head problem
Customer: replied 7 years ago.
what I can get from my manual it a 6 cyc 590 motor? yes, I have had inj pump repaired, injectors, replaced lift pump, and hydraulic pump rebuilt. My oil level raises while in use. It blows a white fog like smoke. Oil is thin and kind of runny. Not sure if it is diesel or hydraulic oil. Kind of smells like diesel though. I have been draining the oil pan after use to allow it to fill up again before the next job. Any way to ck to see if it is diesel or hydro fluid ?
Expert:  DR.Cummins replied 7 years ago.
You can taste the oil or smell it.Diesel will cause it to be thin and runny. Like i said did anyone check your heads while the injectors were out? You could have a restriction in the return line back to your tank or your fuel tank vent might be plugged
Customer: replied 7 years ago.
heads were magna fluxed, oil is thin and runny. How would cause fuel to enter engine? Also would it be one cyc or all cyc? does that cause fog like smoke
Expert:  DR.Cummins replied 7 years ago.
OK were the injector cups checked in the head, There could of been an bad injector hole letting fuel mix with oil In the head, did anyone DYE the fuel to see what cyl is pushing fuel? If you have a restriction the return fuel cannot go back to the tank, there for it will mix with the oil in head area. fog like smoke? Do you mean whitish yes that's fuel
Customer: replied 7 years ago.
no dye was added. pretty sure rtn line is clear. once u dye fuel how do u tell what cyc is bad?
Expert:  DR.Cummins replied 7 years ago.
With Dye you run the unit off a separate fuel source that has the dye in it (5gal bucket is enough to do this test). with the UV light and glasses check around each injector hole with the engine running. IF THE FUEL IS ENTERING VIA INJECTOR you will see the dye glow.
Customer: replied 7 years ago.
is there any other way fuel can enter the crankcase? if a bad cyc is identified can u isolate / disconect the use of that cyc and run on 5 cyc instead of 6? Its an older back hoe and i am at the point where I'm putting to much money in it
Expert:  DR.Cummins replied 7 years ago.
The only way fuel mixes with oil is DRAIN LINE RESTRICTION--PLUGGED FUEL TANK VENT-- FUEL PUMP SEALS--INJECTOR /CUPS/ORINGS-- CRACKED POURES HEADS that's it, no i would not run any engine with cyl cutout it will ruin the entire engine and be off balance ect
Expert:  tj replied 7 years ago.

Hi there. Your engine doesn't have injector cups. It is a smaller cummins it is a 359 cu in engine. More than likely you may have fixed and also caused another problem at the same time. If you are getting whits smoke then the possible causes are: coolant in compression chamber, Injection timing, low compression.

Given this information the first thing to do is check your injection timing. If the timing is off a couple of degrees then the fuel is not being burned all the way causing raw fuel to enter your crankcase. If your timing is correct then the thing to do next is to pull your injectors and preform a compression test. Doing this will find the answer to your problem.

tj, Mechanic
Category: Heavy Equipment
Satisfied Customers: 524
Experience: 10 years of john deere,agco,new holland,cummins
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