Advice - Diesel fuel in my engine oil

[White River Dream]

Newbie from Monterey Bay, CA. I own a 1973 Uniflite 47ft power boat with 2 Cummins 903 v8 engines. I'm getting diesel fuel in my port side motor oil. Has anyone run into this problem or know what the issue might be? Greatly appreciate any input.

 

[Juliet 15]

I had an oil sample from a genset come back saying diesel in the oil. The shop said probably bad injectors, as in too much fuel, or excessive no-load operation.

How did you find out you had fuel in your oil?

If it was a sample I’d ask the shop for their thoughts on what might be the cause, and how much fuel are we talking. If it’s not doing imminent damage I’d be tempted to change the oil, run it under load, and resample.

 

[rochepoint]

A lot of engines have this problem when the fuel pump diaphram has a leak in it allowing fuel to go into the crankcase.

 

[White River Dream]

Thank you for getting back to me. The fact of the matter is these motors have not run for a long time but are what appears to be very good shape. I bought the boat a year ago and I am now firing the motors for the first time. I have been a mechanic for 40 years but not a diesel mechanic. The starboard side motor fired up and ran good and I am not showing any signs of fuel in the oil. When I turned over the port side motor there was a small hole in the oil filter. So I immediately addressed the problem and by doing so also found that the oil was overfull when I drained the oil I found that it had diesel fuel in it. I put all new oil in it. Turn the motor over a few revolutions But he did not want to start. Re-checked oil and now I’m finding that the oil is a little watered down with fuel and I can smell the diesel in it. I have been told by a diesel mechanic that it possibly has a cracked injector he wants me to pull all of the injectors and have them checked.

 

[White River Dream]

Thank you very much for replying. I have been a mechanic for 40+ years but not on diesels. I have been told I probably have a injector issue. But I like your idea with this fuel diaphragm. I have a hard time believing that that much fuel from a injector is getting past my piston. Your answer sounds very logical. If there is a diaphragm that has gone bad and allowing fuel to go straight into the crank case this could save a lot of time and effort removing injectors. Definitely I’m going to look into that. Thank you so muchFor your reply

 

[ofer]

if it was me ill try to diagnose the reason the engine is not starting. the two issue may or may not be related.

 

[White River Dream]

if it was me ill try to diagnose the reason the engine is not starting. the two issue may or may not be related.

As I said previously I am a long-time mechanic but not a diesel mechanic. But I do understand the fundamentals of a motor. I understand the injector pump and what it does for the diesel motor. I understand the injectors and what they do. Without proper fuel pressure to the injectors the motor would not run or at least it would not run worth a crap. If there is some type of a diaphragm in the injector pump controlled by a lobe of some sort from the motor and if a diaphragm was cracked it would certainly explain how a considerable amount of diesel fuel can get into the crank case. I will have to look into this injector pump and see exactly how it operates and what it’s make up is. If anybody knows would love to hear it.Again this is a 903 Cummins V8. The injectors are under the valve cover and operated by a third rocker arms on the rocker arm rail. They are fed by an internal fuel port in side of the head.

 

[ofer]

Without proper fuel pressure to the injectors the motor would not run or at least it would not run worth a crap.

exactly my point first determine if you are getting high fuel pressure into the injectors. you can do that by cracking the line nut feeding the injectors while cranking. there should be fuel squirting out at high pressure.

 

[Ted]

I think you will find the 903 has a PT fuel system , it will have low
pressure fuel supply to the injectors. The high pressure is developed in the injector
by the action of the cam on a rocker(?) shaft.

Ted

 

[catalinajack]

Thank you for getting back to me. The fact of the matter is these motors have not run for a long time but are what appears to be very good shape. I bought the boat a year ago and I am now firing the motors for the first time. I have been a mechanic for 40 years but not a diesel mechanic. The starboard side motor fired up and ran good and I am not showing any signs of fuel in the oil. When I turned over the port side motor there was a small hole in the oil filter. So I immediately addressed the problem and by doing so also found that the oil was overfull when I drained the oil I found that it had diesel fuel in it. I put all new oil in it. Turn the motor over a few revolutions But he did not want to start. Re-checked oil and now I’m finding that the oil is a little watered down with fuel and I can smell the diesel in it. I have been told by a diesel mechanic that it possibly has a cracked injector he wants me to pull all of the injectors and have them checked.

So, you changed the oil and it has diesel in the oil without running the engine. I wonder how a cracked injector, with no fuel pressure or fuel being supplied to it can possibly be the source of the diesel into your sump with just a few revolutions. I'm betting on a torn diaphragm on the fuel pump. Fuel can leak through the tear just sitting there. Fuel pumps are generally not very expensive. I would replace it and reassess. Way cheaper than pulling six injectors only to discover that an injector was not the culprit. Start simple.

 

[White River Dream]

So, you changed the oil and it has diesel in the oil without running the engine. I wonder how a cracked injector, with no fuel pressure or fuel being supplied to it can possibly be the source of the diesel into your sump with just a few revolutions. I'm betting on a torn diaphragm on the fuel pump. Fuel can leak through the tear just sitting there. Fuel pumps are generally not very expensive. I would replace it and reassess. Way cheaper than pulling six injectors only to discover that an injector was not the culprit. Start simple.

That is exactly how I feel too. It is a V-8 so there are eight injectors. But as I said before I have been a mechanic my whole life just not working on diesel motors. I ordered a repair manual but it has not arrived yet. My original thought when I was told that it probably has a cracked injector or something was how conduct much fuel possibly get by my piston. But as you said just sitting there was only a few revolutions I find it hard to believe that it is an injector. And talk about a lot of work to remove all of the rocker rails to pull the injectors out. Thank you very much for your input. I appreciate everybody Who has replied and giving me ideas of what the problem could be. When I find out and get to the bottom of it I will be sure and follow up so that everybody knows and it may possibly help somebody in the future.

 

[sunchaser]

Does this Cummins V 8 have a similar fuel piping setup to the Cat3208? The Cats can leak diesel in the valley area and then into oil.

 

[White River Dream]

Does this Cummins V 8 have a similar fuel piping setup to the Cat3208? The Cats can leak diesel in the valley area and then into oil.

I am not familiar with the 3208. The fuel lights coming off of the injector pump go into a y One goes into a fitting is the front of the head and the other does the same on the other side. Best I can tell is that there is a port running through the head feeding the injectors. In other words there is no bleeding air from these injectors. The injectors are controlled by a rocker arm on the rocker arm rail.

 

[White River Dream]

Sorry about the voice dictation

 

[Solly]

Not familiar with your motor but..... First trace the fuel lines to the motor to see if there is a lift pump. It provides fuel under pressure to the injector pump. Usually is operated by a cam type lobe with a diaphragm inside to pump the fuel. If the diaphragm inside is bad fuel will leak past and into the sump thru the opening to the cam.

 

[Lepke]

Don't remove the injectors. Mechanical injectors have install adjustments and you'll never get it right without a service manual. Buy one if you don't have one. ebay is a good source.

I believe your engine has a gear fuel pump. No diaphragm. The pump is run off the gear train, so if the pump seal fails, fuel has a direct path into the engine. Pumps are about $1300+, but you can buy a seal and gasket kit on ebay for about $50. It's not difficult for a mechanic to replace the seals and gaskets. Inspect the main shaft closely where the seal rubs. They can wear or develop pits that will damage any new seal. Unlikely, but there are sleeves that slip over the shaft and provide a new surface.

If you have fuel and good compression, the engine has to start. As the air is compressed it raises the temperature inside the cylinder to above the ignition temperature of diesel, about 500°F+. Older engines starts in cold weather can be helped by a block heater, pan heater or hot air blown into the intake, like a hair dryer. The higher the engine or air temp, the less it has to raise the cylinder temp by compression.

 

[rgano]

I am sure you are going to resolve this issue as soon as you get completely familiar with the engine, but that aside, I get the feeling you are possibly not familiar with operating a vessel of this size. Your mechanical background is going to see you through as a very effective boat maintainer, because in my mind, enjoying my boat underway is all about routine and preventive maintenance performed. If your wrenching has been concentrated on road vehicles, may I possibly preach to your choir and mention that the reliability of your engines in this boat will be much more crucial than your car/truck? Not as crucial as say in an airplane, but your life could well depend on your boat's engines someday. I am sure you will be going over the engines, but because of the apparent neglect in this case, you will be wise to bring the engines to the highest level of maintenance possible before venturing far. In my humble opinion, that would include cleaning the fuel tanks (you are new to diesel and maybe not knowledgeable about how they can generate filter-clogging goo), replacing all hoses, fuel filters, timing belts, coolers, and pull all electrical connections on them looking for corrosion. Lastly test all the alarms. I am completely unfamiliar with your engine and look forward to hearing of your success here.

And welcome the heck aboard! I spent a nice year at NPS Monterey in 1969-70. Lot of fog.

 

[Island Cessna]

Don't remove the injectors. Mechanical injectors have install adjustments and you'll never get it right without a service manual. Buy one if you don't have one. ebay is a good source.

The 903 Cummins has a PT fuel system. The PT pump provides fuel to the injectors under variable pressure controlled by the governor, through drilled passages in the head for supply and return. There are o-rings on each injector to seal the supply and return fuel. Failure of these rings could cause your leakage into the oil, and loss of prime making it hard to start. Lepke’s advice to acquire the manual is spot on. In the Cummins PT system the individual injector tuning is done by the calibrated oriface in the unit injector, not adjustment of the racks. Removing the injectors to replace the seals may not be a complex process.

Following is a quote from a random internet site on the PT fuel system:
“Fuel supply and drain flow are accomplished through internal drillings in the cylinder heads. A radial groove around each injector mates with the drilled passages in the cylinder head and admits fuel through an adjustable orifice plug in the injector body. A fine mesh screen at each inlet groove provides final fuel filtration.

The fuel grooves around the injectors are separated by 0-rings which seal against the cylinder head injector bore. This forms a leak-proof passage between the injectors and the cylinder head injector bore surface.”

And here is a good U-Tube video on the generic PT fuel system:

https://youtu.be/KzuwdxEJfQA

Bill

 

[White River Dream]

I am sure you are going to resolve this issue as soon as you get completely familiar with the engine, but that aside, I get the feeling you are possibly not familiar with operating a vessel of this size. Your mechanical background is going to see you through as a very effective boat maintainer, because in my mind, enjoying my boat underway is all about routine and preventive maintenance performed. If your wrenching has been concentrated on road vehicles, may I possibly preach to your choir and mention that the reliability of your engines in this boat will be much more crucial than your car/truck? Not as crucial as say in an airplane, but your life could well depend on your boat's engines someday. I am sure you will be going over the engines, but because of the apparent neglect in this case, you will be wise to bring the engines to the highest level of maintenance possible before venturing far. In my humble opinion, that would include cleaning the fuel tanks (you are new to diesel and maybe not knowledgeable about how they can generate filter-clogging goo), replacing all hoses, fuel filters, timing belts, coolers, and pull all electrical connections on them looking for corrosion. Lastly test all the alarms. I am completely unfamiliar with your engine and look forward to hearing of your success here.

And welcome the heck aboard! I spent a nice year at NPS Monterey in 1969-70. Lot of fog.

Although I have been a gasoline mechanic most of my life I have worked on some diesels from time to time and I drive a turbo charged four-cylinder diesel truck. I have restored many boats this is the largest one I have owned I lived on a 35 foot sailboat that had a Yanmar three cylinder diesel in it. The ocean is so toxic. I learned that years ago. Corrosion and maintenance are key. Putting around in a lake in a ski boat is one thing but going out into the ocean is a whole different story. Believe me I get that. These are awesome motors. I love a Cummins in these are 903V eights. I’m looking forward to getting this thing up and going. I plan on checking all the heat exchanger stuff and the transmissions have heat exchangers also. I replaced a paragon behind a 454 Chevy once because The heat exchanger went bad and contaminated the fluid in the transmission completely ruining the transmission. Having done this long enough I just know there’s something going on here and I do not believe it is an injector. My common sense in mechanics tells me there’s no way that much fuel could get by my piston anyway. So today I am looking into these other sources and I appreciate your input. Looking forward to my manual getting here so I can Study it and learn about all the different things on this motor.

 

[ofer]

I am so impressed with your credentials you should be up and running in no time

Although I have been a gasoline mechanic most of my life I have worked on some diesels from time to time and I drive a turbo charged four-cylinder diesel truck. I have restored many boats this is the largest one I have owned I lived on a 35 foot sailboat that had a Yanmar three cylinder diesel in it. The ocean is so toxic. I learned that years ago. Corrosion and maintenance are key. Putting around in a lake in a ski boat is one thing but going out into the ocean is a whole different story. Believe me I get that. These are awesome motors. I love a Cummins in these are 903V eights. I’m looking forward to getting this thing up and going. I plan on checking all the heat exchanger stuff and the transmissions have heat exchangers also. I replaced a paragon behind a 454 Chevy once because The heat exchanger went bad and contaminated the fluid in the transmission completely ruining the transmission. Having done this long enough I just know there’s something going on here and I do not believe it is an injector. My common sense in mechanics tells me there’s no way that much fuel could get by my piston anyway. So today I am looking into these other sources and I appreciate your input. Looking forward to my manual getting here so I can Study it and learn about all the different things on this motor.

 

[rgano]

I am so impressed with your credentials you should be up and running in no time

He's got this!

 

[twistedtree]

I agree you shouldn't just to any conclusions with the injectors. If they were over-fueling enough to quickly get fuel in the oil, I would expects a massive amount of fuel going out the exhaust which is a much easier path than into the crank case.


That said, there are other possible injector related failures that might provide a direct path for fuel into the oil. It's been discussed, but these would be the various seals for the fuel supply and return galleries in the heads.


I think the good news is that the leak is significant, and that will make it easier to locate. I think if you pull the fuel pump, it will hopefully be obvious if fuel is leaking over to the crankcase/timing case side of the pump. So that seems like an easy check.


I'd also consider going ahead and pulling the valve covers and inspecting in there too. You might spot fuel leaking there from one of the injector seals since I think that's the path it would take to find it's way into the crankcase.


Hopefully some of these steps will help isolate where the problem is so you can dig into repairing the actually problem rather than a guess or trial and error.


You might also ask on boatdiesel, or on SBMAR's web site. Both have some very knowledgeable diesel guys who might know specifics about your engine. Also, our own SkiNC is very knowledgeable, and might know your engine.

 

[White River Dream]

I agree you shouldn't just to any conclusions with the injectors. If they were over-fueling enough to quickly get fuel in the oil, I would expects a massive amount of fuel going out the exhaust which is a much easier path than into the crank case.


That said, there are other possible injector related failures that might provide a direct path for fuel into the oil. It's been discussed, but these would be the various seals for the fuel supply and return galleries in the heads.


I think the good news is that the leak is significant, and that will make it easier to locate. I think if you pull the fuel pump, it will hopefully be obvious if fuel is leaking over to the crankcase/timing case side of the pump. So that seems like an easy check.


I'd also consider going ahead and pulling the valve covers and inspecting in there too. You might spot fuel leaking there from one of the injector seals since I think that's the path it would take to find it's way into the crankcase.


Hopefully some of these steps will help isolate where the problem is so you can dig into repairing the actually problem rather than a guess or trial and error.


You might also ask on boatdiesel, or on SBMAR's web site. Both have some very knowledgeable diesel guys who might know specifics about your engine. Also, our own SkiNC is very knowledgeable, and might know your engine.

Thankyou all good ideas�� I am looking it over now . The rocker arm assembly’s are super clean and no sign of Diesel coming up and into the head from around the injector. This is not like working on a small block Ford or Chevy LOL there is not a conventional fuel pump mounted to the block like you would find on the gas motors I am used to working on. The fuel injector pump is centered in the galley of the V8 motor. It is bolted with four good size bolts to a casting with a pulley on the other side which is also driving the alternator. Not sure what I am looking at here. Is this the fuel pump. Where is the fuel pump located inside the injector pump.?? Only one main line going into the injector pump quite sizable for that matter. And one 3/8 copper line coming off injector pump and splitting into what looks like two 5/16 lines. One going into the front of one head and one going into the front of the other head. Nothing in between. I have heard a lot of talk of rubber diaphragms and fuel leaking into the crank case so that is what I am after at this point it seems very logical to me. But without the manual and still waiting for it I feel fairly helpless as to what I am looking at.

 

[White River Dream]

Not familiar with your motor but..... First trace the fuel lines to the motor to see if there is a lift pump. It provides fuel under pressure to the injector pump. Usually is operated by a cam type lobe with a diaphragm inside to pump the fuel. If the diaphragm inside is bad fuel will leak past and into the sump thru the opening to the cam.

No such animal on this 903 V8. If there is a fuel pump and diaphragm it is going to have to be in the injector unit somewhere. Tracing the fuel line going into the injector pump goes to a filter from there the line goes right to the fuel tank. No in between ‘s.

 

[Island Cessna]

No such animal on this 903 V8. If there is a fuel pump and diaphragm it is going to have to be in the injector unit somewhere. Tracing the fuel line going into the injector pump goes to a filter from there the line goes right to the fuel tank. No in between ‘s.

Have a look at the U-tube video, it clearly shows the gear type fuel pump in the PT system.

Here is a photo of the injector. O-ring failure will let fuel into the oil, and the loss of pressure at the injector fuel oriface will make hard or no start.

 

[White River Dream]

Have a look at the U-tube video, it clearly shows the gear type fuel pump in the PT system.

Here is a photo of the injector. O-ring failure will let fuel into the oil, and the loss of pressure at the injector fuel oriface will make hard or no start.View attachment 122853

OK so what you’re saying is if there isn’t a cracked diaphragm in the fuel pump in the injector pump that could allow fuel to get into the crank case then it could possibly be O-rings on the injectors and they would allow fuel to get into the crank case via what? Passed my Pistons or is there another way for that fuel to get into the crank case from the injector besides going by the piston?

 

[C lectric]

THe 903 is similar to mine, V555M, except for displacement.

I posted a manual for these engines a bunch of years ago on Boatdiesel FOrum.
I can send you a copy in 5 parts if you PM me with your email address.

And yes, I did mine three years ago. I had fuel in the engine oil. PT pump I took to the Cummins dealer and they O/H it.
The injectors I sent to them also, they then sent them to a good shop.
I reinstalled them.

I can Email you that in 5 parts if you PM me and include your Email address.

It is the owners manual and covers several engines of the day including the 903.

As already mentioned there is NO lift pump. The only fuel pump is the PT pump unless some added one.

I will just mention that when I got my PT back I was told there was some minor damage but it did not wreck the pump. Had I not done it then it would have wrecked the PT and the cost would have been far greater.

 

[adornato]

fuel in oil

I am really intrigued now with the problem. Be sure to get back to us when you figure out where the "leak" is.

 

[ProMaritime]

My oil analysis indicated diesel in the lub oil which reduced 15-40W to 5W at operating temperature. Exhaust smoke was observed while running but nearly disappeared at cruise power. A top overhaul and new exhaust valves was the fix. Injectors were ok but bad exhaust valve on cylinder #4 just blew the partially burned fuel out the exhaust.

 

[hughespat57]

OK so what you’re saying is if there isn’t a cracked diaphragm in the fuel pump in the injector pump that could allow fuel to get into the crank case then it could possibly be O-rings on the injectors and they would allow fuel to get into the crank case via what? Passed my Pistons or is there another way for that fuel to get into the crank case from the injector besides going by the piston?

VT903M were the primary engines used in CG 41' Utility boats.

There is no diaphragm on these fuel pumps. The transfer pump is gear operated of the timing gears, the PT (Pressure/Time) pump is not a typical injection pump. It only raises the fuel rail pressure in the common rail 25psi min cranking, 270+psi when you snap the throttle running (must use a 0-400psi liquid filled gauge to test.) The unit injectors then achieve injection pressure by the third rocker arm.

The injectors are inside the valve covers bolted into the heads as was shown above. Three rubber o-rings. If they leak the fuel will flow up into the valve covers quite easily. With the valve covers off this is usually easy to spot as the fuel will flow while cranking & wash the lube oil away from the injector. If it starts you will almost certainly see it.


If one is leaking I would put new o-rings on all in that head at least.
They either leak from being nicked/cut during install or last until the next overhaul. Unless someone over heats that head, they dry out and crack.


This is a link to an explanation of the Cummings PT fuel systems:
https://constructionmanuals.tpub.com/14264/css/Cummins-Diesel-Fuel-Systems-189.htm