LB7 oil pressure

[Spoolmak]

The truck has 85,000 miles on it. I've been using Rotella synthetic 5-40 diesel engine oil since 30,000 miles. When cold the oil pressure is up to 70 psi. It drops to 50 to 55 psi at 2000 rpm once operating temperature is reached. But under load and working harder - like going up a long grade with the camper on - the pressure drops into the 40 psi range.

At idle cold, pressure is about 55 psi, but when at operating temperature, drops to 25 to 30 psi.

These operating pressures seem low to me. For sure they are lower than when the truck was newer.

I asked the service writer at the dealership, and he suggested the lower readings were caused by running synthetic. He also said that despite the lower pressures, the synthetic was providing better lubrication than the regular dino oil at higher pressures.

Should I worry about these lower pressures???

Any thoughts will be much appreciated.

Tor

[dually2002]

I had a noticeable drop in oil pressure due to oil level being a quart low. Oil pressure drop alerted me to checking my dipstick which showed a quart low. Added oil and pressure went back to normal for my engine. Wouldn't think a quart low on a twelve quart system wold cause a pressure drop (5-7psi) but it did on mine.The pressure on my LB7 with 85000 miles is is about 70psi cold start idle --about 60psi hot above 2000 rpm and 40psi at hot idle. I run Amsoil 5-30 diesel oil and their filter. I run over 5000 miles before the oil starts to darken. Have your pressures been like that for a while or are you just now seeing them?

[Spoolmak]

Dually2002

It seems to me pressures have been going down in the last 40,000 miles to the point where I'm noticing it. The level is up where it should be, I'm pretty careful on that. I use either Baldwin or GMC original equipment oil filters. The oil stays clean a long time also. We just returned from a 5000 mile trip with the camper on and the oil is still really clean and the oil life indicator says 60%. I typically change oil every 5000 miles with the oil life indicator showing between 50 to 60% life left.

The engine seems to be running really smoothly, no smoke of any kind, and it has never overheated, no matter how hard it worked.

I just don't feel comfortable with the lower pressures.

Later versions of the engine are designed to run with lower pressures.....

Tor

[Mark Rinker]

It all sounds very normal to me, and I've run three LB7s, over 400K miles.

The oil pressure drop after a hard pull is due to oil temperature increase, and viscosity (thinning) decrease.

[madmatt]

12 qts???? Other then that, all other numbers seem pretty normal to me

[Spoolmak]

Thanks for the responses. I'll try to stop worrying....

Tor

[Mark Rinker]

Try Mobil Delvac - either conventional or synthetic versions - see what happens with your numbers. I am convinced that it thins out less, under same conditions.

[madmatt]

+1 for Mobil Delvac

[JohnC]

If all else is unchanged and the oil pressure is actually dropping over time then that is reason for concern. The numbers you posted are not in themselves out of line. If you have 10 psi at the bearings for every 1000 RPM's the engine will be fine. 45-50 psi on the road is more than enough.

The first thing I'd suspect is the pressure sender getting tired, but if you change it you may end up with yet another different reading. I'd confirm it is in the ball park and keep an eye on it. If it continues to change you need to determine if it's really the pressure changing or just the reading, so you need some sort of baseline to go from.

[Spoolmak]

That's good advice. I think a manual pressure gauge plumbed into the system as suggested on another thread may be a wise next step. That will verify pressure readings and indicate whether there is 'lower' pressure, or a lower reading from the sender.

Thanks for the suggestions.

Tor

[dersark]

The truck has 85,000 miles on it. I've been using Rotella synthetic 5-40 diesel engine oil since 30,000 miles. When cold the oil pressure is up to 70 psi. It drops to 50 to 55 psi at 2000 rpm once operating temperature is reached. But under load and working harder - like going up a long grade with the camper on - the pressure drops into the 40 psi range.

At idle cold, pressure is about 55 psi, but when at operating temperature, drops to 25 to 30 psi.

These operating pressures seem low to me. For sure they are lower than when the truck was newer.

I asked the service writer at the dealership, and he suggested the lower readings were caused by running synthetic. He also said that despite the lower pressures, the synthetic was providing better lubrication than the regular dino oil at higher pressures.

Should I worry about these lower pressures???

Any thoughts will be much appreciated.

Tor

I have 66000 miles and exactly the same problem. but I use non synthetic oil. any body can give us a direction of the diagram how and where to conect the oil pressure gauge to read the actual pressure.

[dually2002]

12 qts???? Other then that, all other numbers seem pretty normal to meDon't know why I said 12 quarts. It take 10 quarts with a filter. That explains why I have extra oil. For some reason I 'am thinking of twelve quarts when I buy oil.