Truck Driving Jobs

bob h · Joined: 15 Oct 2006 Posts: 664 Location: Nb

Mountain Flyer wrote: Big Al and One were both on target... had the truck checked Friday; had one piston cooler that they replaced and they also took the piston out of the oil pump and cleaned it up. The combination bumped my oil pressure from the low 20's to almost 30 p.s.i.. The mechanic said for Cummins about 30# or a little over is average anyhow, so I can sleep much better now... 8) The truck runs well otherwise and has good power; doesn't smoke, and what oil it uses it mostly leaks out, rather than burns from what I can tell.

Anyhow, thanks boys for the suggestions. :)

The cooling nozzle should have shown a "sudden" change in the oil pressure; when they break, it creates a leak in the main oil gallery. If the cause was bearings, the change would come over time... almost unnoticably. Fuel will thin-out the oil (not too common in N14s), if it's a slow internal leak, the pressure will go down as the oil change interval comes to it's end. If the internal fuel leak is severe, the engine oil level will rise (overfull). The thin oil can cause a blow-by condition, which will cause blue smoke from the stack.

Doesn't hurt to at least "inspect" the rod and main bearings (bottom end) at 500,000 miles, especially if you didn't buy the engine new. The engine may have suffered head gasket or rocker gasket internal leaks (quite possible) which contaminates the oil and "wipes" the bearings. Watch the oil; conatminated oil will become sludgy (texture) or milky in appearance.

...Overhaul @ 1,000,000 , bottom end @ 1/2 way to overhaul.

The oil leak to "beware of" is behind the accessory drive pulley... if it leaks, it CAN cause major problems, have it checked right away!!!

Oh, and the 1st step in oil pressure diagnose is ALWAYS checking pressure with a "known good" manual gauge.

Mountain Flyer · Joined: 03 Oct 2005 Posts: 212 Location: Boise, Idaho

I still have low pressure in the N14. The repairs they made ( I posted earlier) helped some... for awhile... but I am now back to running about 25 p.s.i. at cruise speeds. When climbing a long hill on a warm day, if I don't gear down and RPM up sufficiently, I will get a Low Oil Pressure alarm on the dash.

Otherwise, she runs fine and does not use much oil (drips mostly). Previous owner replaced the bottom bearings but I wonder if they botched the job? :roll:

stranger · Joined: 08 Oct 2006 Posts: 59

One way to check for worn main and rod bearings:

When loaded, while driving steady on level ground , at say 1500 or so rpm, give the truck full throttle. Note the oil pressure under throttle.

Let off on the throttle completely and let the engine hold back. Stay the same rpm and speed as you were when at full throttle.

Watch the oil gauge. If the needle jumps more than a couple of pounds you have bad bearings.

This test had been right every time I have seen a 4 to 5 lb or more increase in oil pressure between pulling and holding back at the same rpm.

Mountain Flyer · Joined: 03 Oct 2005 Posts: 212 Location: Boise, Idaho

I will try that test! :)

Truck Driving Jobs

Trucking Jobs

Truck Drivers

Trucking Companies

Class A Drivers.com