Oil Breakdown?

[fireman438]

I'm having an interesting problem. The only thing I can think of it being is oil breakdown. Anyway, I first had it happen the other day as I was driving on a 60 mph road with some rolling hills. I had been driving for 15 min or so, the engine was up to temp, and when i hit a hill, it started to make a rattling that sounded like a rod rattle. I looked at the oil pressure and it was about halfway up the gauge. It also had a severe miss on at least one cylinder as though a lifter collapsed. I let off the throttle and pulled to the side of the road, figuring that I'd be replacing an engine soon. After idling for a few seconds, the noise and miss went away, and I continued on, with the same result at each hill. Any ideas?? As a mechanic, this is rather perplexing, since usually an extended length between oil changes with a full crankcase causes no oil pressure issues (not good for the engine, i know). Thanks for any info.

 

[tractorman86]

actually kinda sounds like it could be a fuel problem. unless it is low i dont see how oil could do that, what kinda oil are you using?

 

[69dieselfreak]

fuel filters possibly when was the last time u changed them

 

[Mr_Roboto]

How is your oil level?

I have found that if the level gets low in the IDI's the oil will aerate which will make a marginal lifter "collapse" giving the poor running and knocking that you describe.

 

[Diesel JD]

Or the lifter could just be trash, they were not a very good design on the 6.9/7.3 anyway and running the oil level low, extending the interval too much or using a regular gasoline type motor oil all make this issue worse. It could also bea bad fuel filter or a tired injector. What oil and how long have you had it in there?

 

[fireman438]

I run Shell Rotella T 20W-50. How long is a good question. my spedo doesn,t work (worn out drive gear on t-case output). I'm doing a much needed oil change today, so I'll let you know how it works out. BTW, the oil level was fine, and the knocking was coming from the lower center of the firewall as I heard it from in the truck while driving.

 

[RLDSL]

Most likely it's just a slobbering injector. run a stout dose of cleaner through your fuel tank and see what happens. A slobbering injector on a diesel makes a sound like a gasser about to throw a rod.

 

[fireman438]

I forgot to mention that the problem starts and leaves gradually, and that the oil pressure seems to get lower as the engine/oil warms up.

 

[RLDSL]

I forgot to mention that the problem starts and leaves gradually, and that the oil pressure seems to get lower as the engine/oil warms up.

Yup, sounds about right. and it's normal for oil pressure to get a bit lower as the engine warms up.

Pay close attention to your throttle position of your foot and rpm range when the noise starts, that's usually the dead giveaway that the injector is sticking when it starts and stops in about the same range

 

[RLDSL]

Usually a stout dose of cleaner in the tank will do the trick, for really nasty ones a treatment with about 3 or 4 cans of Diesel Purge ( doesn't go in the tank, you have to rig up a test rig with some hoses directly to the lift pump, the stuff goes in straight and does some serious cleaning ) will do the trick.
If that doesn't do it, it's time for some new ones.

 

[Mr_Roboto]

Just a note, unless you have an aftermarket oil gauge any changes that you see in the gauge reading are due to voltage and resistance fluctuations. The factory gauge is hooked to an on/off pressure switch.

 

[fireman438]

Well, I did get my oil change on Sat. and found just a tad of "extra" oil, like maybe 3 qts. So, I believe I have a shaft seal from my IP leaking fuel into the crankcase, which is causing a dilution of the solution, and thus low oil pressure and all of the problems I've been having.

 

[Diesel JD]

Hmmm, best keep a very close eye on that oil level. If that is in fact the case you'll be able to tell by the dipstick before long. If it is then you're going to have to park the truck or replace that IP sorry to say.

 

[subway]

more than the injection pump can add fuel to your oil. the lift pump is a more likely suspect.

 

[fireman438]

The lift pump is new about 5,000 miles ago, not to say that it hasn't developed a diaphragm leak. However, the fuel system has unknown mileage and with ULSD here in WA state, I have a feeling that my seals are getting chewed up, as can happen to these aged fuel systems without updated seals. I'm also feeling a rough idle every now and again, so I'll be replacing my fuel system in the near future anyway. I've also noticed that the oil pressure is higher with the fresh oil change, so I'll keep an eye on the oil level. I'll kepp you all posted. And thanks for all the input.

Rich