Oil used and fuel pressure

20k is going pretty extreme on a Cat. But…are you adding a gallon as soon as it’s a gallon low? Have you ever tried running it with the dipstick showing a gallon low and see what happens? Cats kinda had the reputation for burning a gallon off and just staying there until service. But if you’re really burning a gallon every 1000 miles once past 10k then your engine is telling you to stop doing that. You’re basically doing an oil change without changing the filters.

 

For the non mechanic (that would be me), I have to ask, why are you looking at fuel pressure when you’re worried about oil usage? Wouldn’t you pay more attention to oil pressure?

Related, I drive a Peterbilt 389 and with fresh oil, the oil pressure is around 60 psi at 70 or so mph. The older the oil, the less pressure until it gets close to service being due where it ends up at around 40 psi at 70 or so mph.

I told the boss man (owner of the truck) about this and he says it’s fine. They’ve had the oil analyzed at different mileages and said it’s good to go.

Go figure...

 

Your fuel pressure is fine. Maybe a touch on the low side but nothing to be concerned aboot.

I always figure once the truck starts burning oil it's time to change it. So if you go 10,000 with no usage then start burning it after that I'd change at 10

 

I ran Rotella and switched to Delo. Seems to burn a little less and perhaps less blow by. Doesn't smell as much out the blow by anyway.

Lot of guys say Rotella is junk nowadays. I dunno

 

Viscosity breakdown basically means when oil is old, it gets thinner, which means it has an easer time fitting thru gaps. So it can disappear (escape) quicker when it's old. Im no expert but my understanding is that it could also simply start vaporizing inside its compartment at normal operating temperature when its old, escaping by slowly losing its liquid form and escaping as a gas or mist.

The other thing about viscosity breakdown is that it means it's losing its ability to protect engine parts from wear, which is exactly the function it's supposed to perform.

So backing up what everyone else said, just from a different angle.