guy's, my 96 4.9 six runs great except for this one problem. oil pressure at cold start is about 40 to 45 lbs. as the engine heats up the pressure slowly goes down. fully warmed up cruising at 40 to 50 or so the psi is about 15 and drops to 5 at idle. I suspect oil pump, but i'me not an expert on 4.9s. i have changed pumps on 390's and their a bitch, jack the engine, make sure rods aren't hitting etc. the 4.9 seems to have more room to lower the pan if its the pump. also the guage is a direct pressure guage with no sender and i use 10-40 oil. anyone got advise or can it be driven like this???
tony

 

The pan will be harder to remove than the 390, IMHO. Make sure you look at the bearings when you are under there having the oil drip in your face.

 

I agree with checking bearing clearances. Oil pump should be the most lubricated item on the truck and my first guess would be excess bearing clearance and not an oil pump.

 

by checking bearing clearance, do you mean the rod bearings? i have no clue on doing that and can the bearings be replaced without further teardown or is a rebuild in the cards? by the way the engine runs very smooth and quit with no rod knocking or lifter clatter.
tony

 

I'm sure you've already done this, but did you replace the oil sending unit yet? If you haven't, it might be worth the extra $10 to eliminate that as being the culprit. I did have that as a problem on my truck once. When it got hot, the needle would go behind the L on the gauge, but the truck ran fine. Upon replacing it, oil pressure readings were a non-issue.

 

no sender, my oil pressure is direct read from block

 

There has to be a sender somewhere, how many miles on motor? My 302 is 45 cold, 10-15 warm idling, 150,000 mi, I have a mech gauge hooked up. -6 you could have no pressure and still run. Also take the oil filter off, cut it open and see whats in there, any silver specs would show bearings going.

 

If you had the pan off you could plastigauge the main and rod bearings. Also it's possible to roll main bearings using the oil feed hole on the crankshaft and a properly cut down cotter pin. In all honesty though considering the motor needs to be lifted just to drop an oil pan I'd opt for pulling the engine to begin with.

 

its not really a sender, but a brass fitting with atube dirctly to pressure guage. i have to agree its probably bearings cause i tried aoil change with a qt. of lucas stabilizer added and hot it now idles at around 20 and goes up to 35 to 40 when driving . is this stuff safe to use? it sure beats a teardown for bearings which is beyond my means at this time. 171,000 on motor

 

If the mains need replacing, you might as well do a complete rebuild. If you can't get to it, or afford a rebuild right now, I would run straight 30 weight oil and dump in a can of STP. I'll probably get screamed at for recommending it, and wouldn't consider it in an engine in good shape, but it might increase your pressure a bit and gain you some time. with that many miles the engine already has a ton of crap built up inside anyway.