First I apologize for the length of this post. I'll make it brief as possible.

I bought a 1999 Dodge Ram 1500, 5.2L 4WD with 99k miles and drove it for about 2 years without problems. I changed the oil regularly with Valvoline 10W30 oil.

I parked the truck for 1 year without starting it. After this time I checked the fluids, started the truck and let it reach operating temperature. All was normal. Later, after driving 10 minutes (6-7miles) the oil pressure dropped to zero. I shut the engine down immediately and checked the oil. I started the truck after several minutes noting normal oil pressure and drove the truck home.

I changed the oil and filter: Same problem.

I pulled and cleaned the pan, installed a new Melling high volume pump, verified the pump shaft, and cleaned the pickup so that it looked new, inside and out with oven cleaner: Same problem.

I installed a mechanical oil pressure gauge to verify the readings.

I pulled the pan and checked the pickup height. The pickup was tight, and the pump was tight with a gasket. I pulled the valve covers. The smooth black crust on the valve train and head concerned me. I cleaned the head thinking the oil was being held under the valve covers and running the pump dry. Same problem.

I pulled the pan to check if the pickup had ingested anything and applied teflon tape to the pickup threads as a precaution. I pulled the intake thinking the black sludge was keeping the oil thererain holes. No problems. With the intake removed I was able to drive the pump with a primer shaft. Oil flow seems to be what I would expect. Oil flow seems to be uniform from the head in the lifter valley and draining properly.

The pressure starts at 70psi(cold) and drops slowly to 60psi(warm) with the high volume pump (60psi & 45psi stock pump). If I drive the truck the pressure drops slowly to zero and stays there. At a 3000rpm+ engine speed, no load, the oil pressure drops rapidly to zero then stay there. I may be hearing the oil pump cavitate or chatter at zero pressure. I assume it is running out of oil but as near as I can tell there is always oil in the crankcase, however it’s difficult to determine with the engine running.

I’ve tried running 20W50 oil with no change. Crankshaft bearings don’t make sense in this case, however I’ll check the endplay tonight as I saw on another post. If crankshaft bearings were at fault, why would the pump cavitate/chatter? I’ve put an incredible amount of time into this problem already. I wanna’ drive my truck again!

Thanks,

 

I just thought of something, after posting in your other thread earlier. Have you checked the oil pressure relief valve? It could be bad. I can't remember if it's part of the pump on the V8s, or if it's in the front cover like it is on my V10.

 

Suprize, 'Rom is right again [8D].


[IMG]local://upfiles/948/A05FEAAC4E244F3A9083CB9424C48F0C.jpg[/IMG]

 

Yea, I thought of that, but I changed the pressure relief valve when I changed the pump.......right?

I didn't get to check the endplay last night. I got home very late.

On a positive note, I'm getting pretty good at pulling the pan off on this truck. It only takes about 15-20 minutes now.

 

I had a somewhat similar problem in of all things,a 225ci slant 6.I dont think this is your problem but I will throw it out there anyway.I had oil pressure on start up but it dropped to zero within a couple of minutes,turned out a cam bearing had loosened and spun blocking about 90% of the oiling hole.My top end was also bone dry as you described.The closed off oil hole was causing high pressure and the relief valve was letting the oil by-pass back to the pan.The v8 and slant6 are quite different engines though,so I dont know if this could be your problem or not.

 

Does any one know what pressure the relief valve is supposed to trip at?
Or if it resets itself if pressure returns to normal? I expect it would, since it's only a spring/piston/valve assembly.

I'm getting nice oil flow throughout the engine. The valve train was nicely oiled even before I cleaned the sludge. I just thought that by some chance the sludge slowed the oil from draining back properly and causing a "low oil" situtation in the crankcase. It was a nice thought anyways.