Fuel in Oil – HELP

Alright guys, I seem to have small amounts of fuel in my oil. I hate to start another thread about this, but I have read the majority of the others and am still a little confused. I also read through the IP TM (TM9-2910-226-34).

Here is what happened:
-Did an oil change (first one under my ownership), drained out a little over 5gal of oil. Looked and smelled like oil.
-Sent oil off for analysis, came back that it was 7% diesel fuel – not good.
-Researched on SS and read the TM.

It is my understanding that there are 13 places that fuel can contaminate the oil:
1) FDC
2) fuel shutoff actuator o-ring
3) HH o-rings (2 of them)
4) boost fuel pump seal
5) flame heater (if equipped)
6) fuel injectors (6 of them)
7) plunger in the HH

Above seems to be in order of likelihood. So, some immediate eliminations, no flame heater, truck purrs like a lion, so unlikely it would be the plunger or fuel injectors. Did some additional testing:

-Took off the fuel stop cover, engaged the lift pump (electric tank pump), and watched. There was no apparent drops or leaking of fuel from the HH o-rings or fuel actuator o-ring. I left the lift pump on for several minutes.
-Removed the FDC (mine is not bypassed), engaged the lift pump, and watched. There was no apparent drops or leaking of fuel from the friction fit seal at the top of the limiter arm. I left the lift pump on for several minutes.
-Unbolted boost pump and slid it out to the steering gearbox, ran the lift pump and watched. A little bit of oily liquid oozed out, but no signs of fuel running down the shaft of the pump to where I could see. Again left the pump on for several minutes.

Nothing seems to be leaking, and it sounds like from the posts and few videos folks put up that these seals should be obviously leaking with the 10psi from the lift pump behind it.

Confused, some thoughts I had:

I did not have much fuel in my oil, only ~1qt, so I caught this early. Could it be that some seal is just starting to fail at the higher pressures of the boost pump or the HH and I just will not see it with the tank pump pressure?

My truck can be a little hard to start sometimes, so I’m wondering if my tank pump is getting tired and not actually getting fuel behind those seals during my test. Should I run the truck briefly, then stop it and leave the tank pump on, and re-test so I know fuel is there?

My truck also smokes a lot when cranking and first starting. Could I have a leaky injector that is ever so slowly leaking a little bit of fuel into the piston and past the rings every time the truck is parked? If so, how do I tell which injector?

How much oil pressure does the IP see? Could I leave the fuel stop cover or FDC off and inspect it with the truck running so there would be 60psi from the boost pump behind these seals? Or will I get everything covered in oil and not get proper pressure/lubrication to the rest of the engine? I have a feeling that this is not really a good idea.

Should I just wait and closely monitor oil levels and see if the truck starts to make oil at a noticeable rate? I have no idea how long the old oil was in the truck (but I’m guessing 5yrs+ from former owners comments), it might have taken years to build up this much fuel.

Or should I just break down and replace all the IP seals and bypass the FDC? Probably will make me sleep the best at night. I don’t have a pryometer to adjust the IP fuel flow, so I would prefer to not bypass the FDC just yet, and getting the boost pump out seems to be an ordeal.

Any thoughts, comments and recommendations from experience would be appreciated. I’m registered for a 4th of July parade, so need to figure this out soon or there will be truck load of disappointed kids.

O rings in the HH that's my two cents , also bypass FDC easy to do

Only place fuel is on one side and lube oil is on the other is the density compensator.
By-pass density compensator.

[QUOTE= Could it be that some seal is just starting to fail at the higher pressures of the boost pump or the HH and I just will not see it with the tank pump pressure?
Any thoughts, comments and recommendations from experience would be appreciated.

You are on the "good" side of the problem.
Just change the oil and monitor, Who knows what got put in the engine in five years or more. The drain oil analysis was done and revealed the fuel in the oil. Perhaps in 20 more running hours it will indicate none.
Best advice is usually "don't fix it if it ain't broke"

frank8003 said:

You are on the "good" side of the problem.
Just change the oil and monitor, Who knows what got put in the engine in five years or more. The drain oil analysis was done and revealed the fuel in the oil. Perhaps in 20 more running hours it will indicate none.
Best advice is usually "don't fix it if it ain't broke"

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Thanks. I was leaning towards this as I thought about it more after posting. I took the truck on 2 short trips today, checked the oil level after both and found it to be spot on the full mark. If the truck is making oil it is making it very slowly. Will continue to monitor and post any updates as to the culprit (if any).

Let us know what you find after a couple of tank fills, and you have a baseline. I'm interested in water leaking into the fuel tank somehow, I think I need to replace gasket on the tank cap any suggestions.

It has been about a month, and I have used ~1/2 tank of fuel (truck does not get driven too much). I have been religiously checking the oil level after shutoff, and it is always right where it should be. If the LDT is making oil it is making it unnoticeably slow. I think that frank8003 is right and this was most likely a case of who knows what happened during previous ownership - looks like I can put off that IP rebuild!! I will continue to monitor and update if anything else happens.

Thanks all for the input.

This started to happen to me and went from bad to worse quickly. I suspected my FDC since power had dropped off; I was running about a 75/25 mix of WMO/diesel. I bypassed the FDC and it went away and I haven't looked back since. It is lower on power with the oil mix, but it's an acceptable loss.

My main reason for adding a magnetic fuel filter was to eliminate hard particles that could potentially damage the many honed/lap fitted surfaces within the fuel system, primarily the FDC.
Agree, bypass the FDC.

"Or should I just break down and replace all the IP seals and bypass the FDC? Probably will make me sleep the best at night. I don’t have a pryometer to adjust the IP fuel flow, so I would prefer to not bypass the FDC just yet, and getting the boost pump out seems to be an ordeal."

You are right, but could dial back the adjustment three or four flats to be on the safe side, until you can install a pyro. Alternatively, being aware that the fuel is turned up some is probably 3/4 of the battle. Don't floor it at low revs, dont lug the engine up hills, stay away from full throttle for prolonged periods and it is unlikely that bad things will happen.

Since I did my oil change I have put 171mi and 9hrs on the engine (interestingly that puts my average speed at 19mph), and last time I checked the oil level it was about 2qts low. I do not have any obvious oil leaks, no puddles/stains when parked, no oil all over the engine, but I do have blue-ish exhaust, especially during warm up. Given this I assume I am burning the losses, and this seems a bit excessive to me. I checked the operator TM (TM 9-2320-361-10) and did not see anything about oil consumption rates. Does this seem above par from what you guys experience?

MDdeuce said:

Since I did my oil change I have put 171mi and 9hrs on the engine (interestingly that puts my average speed at 19mph), and last time I checked the oil level it was about 2qts low. I do not have any obvious oil leaks, no puddles/stains when parked, no oil all over the engine, but I do have blue-ish exhaust, especially during warm up. Given this I assume I am burning the losses, and this seems a bit excessive to me. I checked the operator TM (TM 9-2320-361-10) and did not see anything about oil consumption rates. Does this seem above par from what you guys experience?

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Your not running the engine hard enough. The rings need pressure to seal properly in all diesel engines. So at least once a month take it out and go for a good long drive preferably over a mountain ! Or load it up with anything heavy ( volunteer your truck to help move things for your friends) and drive it. This will help reseal the rings and stop the burning of your engine oil.

For the love of all things Multifuel bypass that FDC soon. You will sleep better.

rustystud said:

Your not running the engine hard enough. The rings need pressure to seal properly in all diesel engines. So at least once a month take it out and go for a good long drive preferably over a mountain ! Or load it up with anything heavy ( volunteer your truck to help move things for your friends) and drive it. This will help reseal the rings and stop the burning of your engine oil.

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Thanks. The truck lives an easy life, mostly Sunday drives and parades. I'll have to find heavy stuff or some mountains for the weekend drives.

MDdeuce said:

Thanks. The truck lives an easy life, mostly Sunday drives and parades. I'll have to find heavy stuff or some mountains for the weekend drives.

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Plenty of heavy stuff to bid on and then carry home on the back of your truck! It is to keep my truck running well, honey!

Checking the boost pump seal Is next since I'm gaining oil again. Which tm do I need to look through? FDC bypassed, HH orings done, fuel shutoff o ring when I did HH. No flame heater. Boost pump. Do we have a thread for checking that without taking IP off? Noticed my oil pressure slowly lowering and checked oil and it's thin again.

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TM calls for removal of booster pump and 60 psi of fuel put through it. In tank pump might not be enough if the seal is not that bad. Might take all 60 psi to open up the seal. Not a fun job.

Floridianson said:

TM calls for removal of booster pump and 60 psi of fuel put through it.

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I'll just pull boost pump and replace the seal on shaft and make sure I have no real wear. Anything else I should look at while IP pump is off truck?


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Engine to IP oil feed line.

Blackbear said:

Let us know what you find after a couple of tank fills, and you have a baseline. I'm interested in water leaking into the fuel tank somehow, I think I need to replace gasket on the tank cap any suggestions.

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Fuel cap gaskets are about $6 on evil-bay and from supporting vendors, so just go ahead and replace it.