oil pressure drops when hot

[01hillbillycummins]

it only happens when my engine has been working, or just cruising for a couple hours at 65ish. Whenever i stop, the oil pressure drops way down, the light comes on, and the truck comes real close to dying. however, when its cold, or just driving around town, it does fine. oil psi is fine, and the truck idles fine. It has 15w40 in it. Also the PO put a big bypass for the oil system on it. No idea if this would change it at all. Should i try a thicker oil or a synthetic next oil change?

[CumminsPower59]

I would double check the pressure with a known good mechanical gauge, may be the oil pressure sending unit on the fritz.

[Tacoclaw]

My guess is that your OP drops because your engine is dying, not the other way around. An engine that doesn't want to idle after coming to a stop once warm is typically the result of a tired Injection Pump.

Checking it with a mechanical gauge would be an easy thing to do, just so it doesn't accidentally get over-diagnosed.

[01hillbillycummins]

the PO put one in, kinda hard to see but its the lower one. the upper is a coolant temp gauge that doesnt work. and i cant take it out because he cut a nice hole through the dash




is there a way to check my LP to see if its tired or not?

[cmann250]

is there a way to check my LP to see if its tired or not?

Yes, get a gauge hooked up and it should put out 3-5 psi right out of the LP. A drop of 2 psi is ok after the filter. I read that Philip had a stock LP that put out 7 or so psi, so I guess they vary. These measurements are at cranking speed, btw

[PToombs]

#1, LP pressure should be 5-7 at idle, no less than 3 at WOT. Caleb, you better make some crib notes, this is about the 3rd time you've screwed this up.
#2 what is the engine idling at warm? It may be too low, that would cause the oil light to come on. IIRC, it should be at 750-800 rpm in drive with the AC on.
And like Taco said, it may be the injection pump, not the lift pump. Check the simple stuff 1st and let us know.

[cmann250]

#1, LP pressure should be 5-7 at idle, no less than 3 at WOT. Caleb, you better make some crib notes, this is about the 3rd time you've screwed this up.

Forgive me for going by what my '89 FSM says Pete, it has been noted Of course I can't figure out the scanner to show what the FSM says, whether it's right or not

I said to hell with fuel pressure concerns and put on a Low Pressure Piston Pump

[01hillbillycummins]

thanks guys, ill see what i can find out. i have no idea what it idles at warm, no tach. However, it only happens after being run steadily for a while. half hour drives it wont happen.

[PToombs]

Caleb, I went by the 93 FSM. I just can't believe Dodge in their infinite wisdom changed the way to check the fuel pressure on the same truck 4 years apart......
My apologies for the harassment.












Yeah right!

[cmann250]

No offence taken! I've had plenty of problems with the Dodge parts of my truck, but I haven't had so much as a hiccup out of the Cummins engine. Thanks for providing the FSM counter evidence. Oh how I love Chrysler and their inconsistancies!

3-5 does seem low