Need help with NHC-250 cummins

[5tondeuce]

Hi all,
I recently purchaced a 1971 M818 tractor with the 250 cummins. It was
being stripped for parts for other trucks but I convinced the guy to sell it to me. I had it running with a one gallon jug for a fuel source(both fuel tanks are
dirty inside) and I had the fuel return line going in another jug. The fuel is going into the engine clean and coming out the return line with what looks like
motor oil in it. Any and all thoughts on this would be much appreciated.
Thanks in advance
Chris.

 

[Nonotagain]

Probably years of crud and corruption in the IP and fuel lines that's getting flushed out by running the engine.

If you get fuel in the motor oil then I would worry.

 

[5tondeuce]

Thanks nonotagain,
I am hoping thats all it is. I don't know much about the IP on these trucks
and I wasen't sure if oil could travel along the shaft that drives it
Thanks again

 

[papercu]

5 ton deuce???

 

[5tondeuce]

Hey Papercu.
I take it your wondering where I came up with a rediculous name like
5tondeuce. I am collecting parts(I have most of them) to build 4 wheel
steer deuce with 5ton rockwells and 1600 X 20 michelins on 2 piece wheels
Don't worry I am not hacking up a deuce. I bought a deuce from a friend
with a cab, detroit diesel , tranny and transfercase with no bed,axles or
wheels and tires for $100.

 

[Nonotagain]

Thanks nonotagain,
I am hoping thats all it is. I don't know much about the IP on these trucks
and I wasen't sure if oil could travel along the shaft that drives it
Thanks again

No problem.

The IP operates at high pressure so if you have any leaks in the system it will be fuel getting to the engine oil not engine oil getting to the fuel.

 

[5tondeuce]

Nonotagain
That is and interesting statement. Once again not knowing much about the
internals of these system is it possible to get fuel in the engine oil and if so how does it get there?

 

[Nonotagain]

Nonotagain
That is and interesting statement. Once again not knowing much about the
internals of these system is it possible to get fuel in the engine oil and if so how does it get there?

An internal leak in the IP (bad seal) will cause fuel to leak into the engine since that is the path of least resistance. I'm not sure of exactly how much fuel pressure the IP puts out (1500-2000 psi is common), but any small leaks will turn into a large leak in short order.

Once you get your fuel tanks replaced you should flush the fuel lines since they will probably also be contaminated with the same crud (read rust) you are seeing in the gallon can.

You should probably plan on getting two sets of fuel filters. One set to use for a clean and flush mission and the second set to use once you think the system is cleaned out.

 

[5tondeuce]

Nonotagain,
Thanks again for all the info
Chris

 

[WillWagner]

The above is incorrect. The PT system on the 250 makes 150 PSI max..OK maybe 10 or so more, depending on the pump code. There is only flow at low RPM and it only turns to pressure at higher engine speeds. The pump seals are not as prone to leaking as the injector o-rings. The injectors are fed through the lower passage and returns through the top passage. When an engine has been worked and then put into hibernation, the top injector o-ring, well, all of them, get hard and flat and shrink causing a leak path. There is no pressure in the return, but just the slight restriction of the lines causes the fuel to be pushed past the now rock like, once viton...but only on engines built or repaired after the late 80's, then they are just rubber...o-rings and into the engine oil. The pump seals are very reliable. If the pump seals do fail, the usual symptom is a very hard start, it will act like it is out of fuel because the failed seals let the fuel drain back to the tank.
Just drain the tank, flush it and install some new filters. You'll be OK.

 

[5tondeuce]

Willwagner,
Thanks for all the information(wow, alot to absorb) In my initial post I mentioned I am getting what looks like engine oil coming out the fuel return line into a clear jug. It's not dirty or grungy looking it just looks like a mixture of dirty engine oil and diesel fuel. I am not sure if this is possible but I don't think it is just dirty lines.
Thaks again.
Chris
P.S. Do you think I should be changing the injector o-rings and is there a
injector pump seal kit or repair kit available if needed.

 

[WillWagner]

It is possible, but most likely just old fuel, it turns dark the older it gets. Cummins sells this cleaner that we tend to call "diesel douche" I have seen it raise HP by 30 w/o a tune up. You can buy some of it and follow the directions, then run out of a clean bucket of fuel to see what it looks like. It will be darker after running through the engine just because the sulfer...well, what's left of it, in the fuel truns dark when heated. Remember, the return dieselgas is the stuff left over from the cooling process thaet the PT system uses...lotsa flow for leeping the F/P and injector parts clean and cool. If it were mine, i'd flush the tank and run it.

 

[5tondeuce]

Thanks Willwagner.This is all very useful info.
This is a great site with great people!! Thanks to all for the help.I hope as I gain Knowledge of MV I can be of some help to others!!!