Low oil pressure Question.

[Chris142]

Ok, With gasoline engines we are told that 10psi for every 1000 rpm is acceptable.

Is this the same for Diesel engines? Since the cylinder pressures are so much higher in a diesel how does this affect the oil pressure.

Reason I'm asking is that I found a Peterbilt that I'm interested in. The owner claim that the engine has low oil pressure but that it still runs. The engine is a 855 cu in Cummins @ 400hp.

The truck is 300 miles away from me and if I was to buy it I would need to drive it home.

Would 15 or 20 psi be enough for my trip with just the tractor since it would be running @ 1500-2000 rpm? Or would I need more oil pressure to prevent any more damage?

 

[Cyprs]

I have a 92 5.9 Dodge Cummins diesel, this engine needs 10lbs psi idle and 30 psi full speed, most 5.9 or about 350 Cubic Inch Cummins need this, cant speak for that 855 C.I.er though. Synthetic oil can make oil pressure bit lower too, just more oil flows through clearances as it is explained to me in numerous forums here, a heavier grade dino oil may help increase oil pressure. Sorry, cant tell you if the trip would be safe for your Cummings. A Cummins implement dealership mechanic/tech may be able to help.

Cyprs

 

[Chris142]

I sent the seller a message asking about the oil pressure. FWIW it's Ebay item# 4513933487 if anyone wants to look.

I have not heard back from him/her yet. I'm kinda leary about buying something with a known problem. I know that low oil pressure is usually caused by worn bearings, a worn crank or a worn pump. I would think that if it was a simple fix then they would have repaired the problem to get more $$$ out of the sale.

Maybe it needs a crank! I really don't want to get THAT involved with a big displacement engine just yet since I have no place to work on it right now.

Could also be cam bearings which I'm sure would be real expensive to replace.

Could also be something simpler like fuel diluted oil from a bad injector or possibly somehow a 5w-30 oil got dumped in the pan instead of 15w-40.

Probly pretty unlikely that it's a problem with the oil it's self and more likely that it's a mechanical problem.

I'm gonna keep waiting and see if I get a response from the seller and go from there. Maybe they will give me the scoop?

 

[wwillson]

I think $5000 is way too much. Have you looked at the price of a modern used class 8 truck? If the reason the oil pressure is "low" is that the engine is plain worn out, then you'll be spending some real money to overhaul it.

Wayne

 

[Chris142]

quote:

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Originally posted by wwillson:
I think $5000 is way too much. Have you looked at the price of a modern used class 8 truck? If the reason the oil pressure is "low" is that the engine is plain worn out, then you'll be spending some real money to overhaul it.

Wayne

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Actully the narrow nose Petes are really expensive! Most are starting @ 10K and going up from there!

I'm in SoCal and the used and worn out late model Freightliners are going for 25-30K! Ain't no way I can afford that. Used Petes with 1,000,000 miles are selling for 60K.


I like the look of the older trucks and this would be more of a hobby right now. I don't plan on putting it on the road for a long time but I want something with a good drivetrain to start with.

 

[widman]

You are right, almost all causes of low oil pressure are enlarged bearing clearances from wear. I once saw pieces of a home made cork gasket blocking the flow (CAT 120 B Grader), but you are more than likely looking at a big repair. If it's a trip or two you are worried about, you can always increase the oil visc. We often go up to 20W-50 when the 15W-40's start losing presure and people don't have the money for the repair.

 

[Chris142]

I've sent the guy 2 emails asking for more info about the low oil pressure. He has not answered either.

If he would tell me what the pressure is fully warmed up or atleast tell me what he thinks is wrong with it or what he was told is wrong I'd be alot more interested.

By not answering my mail I wonder if it is terminal or atleast alot more work than slapping in some new bearings and a new oil pump.

I really don't want to be bench pressing a crankshaft in the thing while laying in the sand and tumbleweeds, fighting off rattlesnakes.

 

[Steve S]

Chris look in the central valley for better deals, used trucks don't hold their value. Don't get a truck untill you get good paying freight to haul,then look for a newer one as down time and repairs cost big bucks.