3126B Oil Pressure Issues

[bpu699]

Ted, quick question…

If you drop the oil pan, how easy is it to shim the oil pressure relief valve?

As I mentioned, my oil pressure isn’t low enough to necessarily consider a new oil pump. But, if shimming the valve raises pressure 5 psi that would be worth it. 2 washers costs 10 cents .

Do you need to remove the oil pump?

I have shimmed the oil relief on my older Porsche, and it made a significant difference.

[Ted DuPuis]

Originally Posted by bpu699

Ted, quick question…

If you drop the oil pan, how easy is it to shim the oil pressure relief valve?

As I mentioned, my oil pressure isn’t low enough to necessarily consider a new oil pump. But, if shimming the valve raises pressure 5 psi that would be worth it. 2 washers costs 10 cents .

Do you need to remove the oil pump?

I have shimmed the oil relief on my older Porsche, and it made a significant difference.

It's been a while since I've had that apart and I can't remember. I also didn't try shimming the pump. However, I believe that was doable with the pan removed without removing the pump itself.

Something worth noting is that when I replaced the pump, it was to an updated style. I forget the name of the different types, but the new style pump is what you find in basically every modern engine and is a better design. The old one was your standard positive displacement gear pump. I believe this was an update Cat did with the C7.

Basically, shimming the pump will change your max pressure. But if your overall pressure at higher RPM is sufficient, shimming the pump may help a little bit, but won't help a ton.

[bpu699]

Well, finally saw a professional CAT/Cummins fleet diesel mechanic. Mentioned my oil pressure being 36-40. Occasionally 34 if really hot.

Asked for suggestions to raise pressure, shim, new oil pump, etc...

He just smiled and said "don't bother. These motors do fine and most have lower pressure. Also, oils have gotten much better since those recommendations were even made..."

He mentioned that many newer diesels run at 30 psi cruising down the highway.

He reiterated, "If you don't have enough pressure, the HUEI system will let you know." It just won't run or run very poorly.

Here's an interesting read. Many trucks have an oil pressure of 30-40 while cruising! I didn't know it was that common:

https://freightviking.com/normal-oil...re-semi-truck/

[omarrufo]

i bought a 98 UltraSport Freightliner XC 3126 with under 50K miles on it..dash gauge even when cold would never even go anywhere close to middle (has dial with L 'normal' H markings), when hot specially after a good workout on hills.. idle pressure would drop to within a 'needle' from Low mark .. put mechanical gauge and cold start up pressure 45 and hot idle would drop to around 12-15.. 1500 rpms to 1800 rpms hot would hit 40 so within specs...but still though too low for my liking... Finally replaced oil pump with new revised style.. cold start idle now 62psi ..hot idlle holds at 30 psi which is a good 15 plus psi improvement over stock oil pump...with low miles (now just passed 51K miles), did not bother to check bearings, with pressure jump i saw, appears bearings are still in great shape....anyone with low pressure concerns, get a fairly inexpensive pump on ebay for around $240 or so .. easy install, and to make it easier to drop pan, remove crossover transmission cooler pipe and great time to flush and replace coolant as well...

[bpu699]

Can you post a link to the pump you bought? CAT wants $1000 for the updated pump, plus your core.

Anyone have input on the quality/safety of using aftermarket parts? I’d rather use me CAT, but the prices are nuts!

[omarrufo]

this is pump i replaced my OEM one with, gave me a full 15 lbs of increase PSI cold and operating temperature .....it's the new revised style pump ... i have a 1998 UltraSport with 3126 Freighliner XC .... https://www.ebay.com/itm/384095648099

[bpu699]

Thanks