Oil or diesel fuel in coolant res.
 

Went to change my oil today and I noticed quite a bit of oil or diesel fuel in my coolant resevoir. How do I know where this is coming from? The oil looked good, just dirty, no coolant in the oil, but like I said, oil or fuel in the coolant. I have not noticed any loss of performance, but my MPG are not real great, I attributed that to the short trips and stop and go stuff that I have been doing lately. Advise? Suggestions? HELP!

gotta determine if its diesel or oil. Sounds as though, its either your oil cooler is leaking/went bad or your injector cup/s have a crack...more "seasoned" members will chime in.

If it is diesel in the coolant, you more than likely have a cracked injector cup. If it is oil, it is most likely the oil cooler on the side of the block.

Cracked cups are pretty common, but require the injectors to be pulled to swap them out.

Remove the cap and sniff the coolant. Does it smell like diesel? Oil floats on top of water. Stick a paper towel or your finger in the coolant and see what fluids you pick up.

yes, smells like diesel, very runny, not thick like motor oil. I also noticed that the entire left side of my engine bay and axle, inside of the wheel well, that entire area is covered with what looks to be diesel fuel.

Any other ideas? I am assuming that I should not drive this until I get it fixed, correct?

Well if by "left side" you mean the Drivers side, that sounds like the oil cooler to me. I know you said it "smells" like diesel, but the area you described is where the oil cooler is mounted. The cooler is a fluid to fluid cooler meaning the oil is circulated about the coolant to disperse heat. The whole assembly is sealed with big O-rings that fail, causing the two fluids to mix.

Remember, unless the truck's been sitting for a while, the oil will be "mixed" with the water until it settles back out. It gets beat pretty hard by the vane water pump. What does you oil look like?

If "left side" meant Passenger side, you have a different problem... may be your fuel bowl drain valve O-rings are shot.

That can be from the diesel overfilling the degas bottle, then overflowing. Since the diesel is on the top it spews first.

Subscribing.

subscribing and learning...:)

Bump for more ideas / help.....

Could you elaborate on which side of the engine bay you were referring to by "left side"? Is your coolant reservoir filling up/over full?

Hi Earl, went through this a year and a half ago. If it is overfilling the degas, the fan will move it. I panicked, but through some good info here and dieselsite(i think) was able to make a good decision.
The inj. cups, if cracked, will allow fuel to get into the coolant because the fuel is under greater pressure. I had a local diesel shop do the job because if I would have bought the tool and parts i would have been within a cpl. hundred. You should just replace them all
because it it very hard to see the cracks, and they expand under heat and pressure.
I did all the remaining stuff myself, flush and fill coolant, new g.p.'s, oil change.
All that adds to the cost. Also I had a decent relationship with the owner.
( I orig. thought I had a cracked block)

Sorry, passenger side.

Riffraff Diesel has new type loaner tools for removing and replacing injector cups that doesn't require the removal of the rockers.

Here's how to find individual cups that have a leak. LINK Tools in this link are different then those supplied by Riffraff.

Or change all the injector cups and 0-rings for piece of mind.