Oil pressure @ hot cruise

[cscmc1]

I know this has been touched on before, and I apologize for bringing it up again, but a search idn't turning up the threads.

Made my first "long-ish" trip (just 50 miles each way) in the '89 yesterday, and at hot idle, I was down to about 10 lbs of oil pressure at the lowest. It would quickly rise to about 30 pounds by 2K rpm, and then would just barely hit 35 pounds to about 2.5K. It hit 38 pounds or so a few times on runs up closer to 3K.

Sound reasonable? Or might a new oil pump keep the pressure closer to or a bit over 40 pounds?

Anyway, the good news is that the truck ran just fine and delivered my fiance, myself, and our new furniture home w/o incident!

 

[cscmc1]

n/m... I found the post I was looking for! Looks like I'm a bit on the low side but not at critical low pressure just yet... agreed?

Tks,

Chris

 

[tonkadoctor]

As a rule of thumb in racing we liked to have 10 lbs of oil pressure per 1000 RPM.

In the couple hundred engines I've rebuilt over the last 25 years I've never found low oil pressure due to a bad pump that most people think the problem is when they bring them to me but I'm sure some have. 99% of the time it was due to worn Main and/or rod bearings and on a couple of occasions I seen it was a worn or broken spring in the pressure relief valve.

I don't know how many miles are on your engine but if you decide to drop the pan to check the pump clearances etc... plan on checking the bearings while you have it open, You can often get away with just replacing main and rod bearings in a well built diesel like these IH engines and get alot more miles on it before a complete overhaul is needed.

It's a pain of a job to do the the engine still in the truck but it can be done.

 

[cscmc1]

Thanks for the tips. I figured maybe I'd get lucky and it might be just the pump since pressure seemed OK at idle and at 2k rpm, but peters off a bit after that. I am seeing over 10 pounds per 1K rpm still, and no noticeable oil consumption (though I have only put about 300 miles on the truck so far). Hope she last a while yet!

 

[fx4wannabe]

You should be fine. Consistency is key. If it always stays the same then I wouldn't worry to much if it starts going crazy getting low then high, then my concerns would rise.

 

[tonkadoctor]

You should be fine. Consistency is key. If it always stays the same then I wouldn't worry to much if it starts going crazy getting low then high, then my concerns would rise.

Just keep an eye on it. Usually when the bearings go it will keep dropping as the as it warms up and often will be at "0" at idle and not much more when it revs.

I also didn't think to ask what weight oil you run. If you're running 5w-30, 10w-30 or straight 30 consider going to a 15w-40, at your next oil change, that is made for these diesel engines like Shell Rotella, Mobile Delvac or Chevron Delo 400 just to name a few. They have better soot control properties among a few other things and don't break down as easily in diesels as some stuff made for gas engines.

 

[Diesel JD]

Yes this si a common question with the 6.9/7.3. We really hashed this out on that other site. From what I have heard its that hot 2000+ RPM number youw ant to look at to judge teh condition of the bearings. It was also determined that if you are over 30PSI at 2000 you should be in good shape. Youa re right tough that 38PSI at 2500 is out of spec for 86-87 6.9s and all 7.3s. What has always been strange to me is that on the '83-'85 6.9s, 30psi was the mion. acceptable pressure at 2200RPM, while they changed it to 40 on the 86 and later 6.9/7.3. If anyone can tell me why they changed specs I would find that really interesting. As to oil, Tonka is right, you need to buy a diesel rated motor oil, your favorite brand and teh weight appropriate for your climate, but just make sure that it is rated for diesels. 15/40 will give you a higher oil pressure most of the time. SAE 30 will give higher readings at cold idle and startup it is some mighty thick stuff then. Either is good provided it is correct for your climate. 10W-30 diesel oil is also used in some very cold climates.