Lost oil pressure in my stroker motor

[dstryr]

Guys, give me some ideas please on where to start looking....this happened in August and I got a little down about it and have left the car in the garage for 3 months so I could pout

Edit: Motor is 440=>505, Comp XS290S cam, comp EDM lifters, and HS 1.5:1 roller rockers, Source rotating assembly, high volume oil pump, do not recall p/n right off. 

Here's what's going on...drove the car to a show and as usual, oil pressure was 75lbs cold and 50ish at idle and right at 75psi at cruise, 3500rpm +/- when hot.  I left the show and decided to cruise a while, 96*F but car runs cool and after about 25-30 miles noticed the oil pressure was down around 70 at cruise rpm, then a hair under, then as the miles ticked off continued to drop slightly until when I got home psi was under 20 at idle and just over with rpms up.

I have both mechanical and idiot light sensors.  Once home I let the car sit outside to cool and then started the engine and both light and gauge took several seconds to go out(light) or register pressure(gauge) so I moved the car in and shut if off and haven't moved it since.  I did take the oil filter off and it is clean and the rockers 'appear' fine from pulling the driver side valve cover.  I heard no obscene noises over the exhaust.  

Where to start?

Many thanks in advance!

[ws23rt]

Where to start?---The oil pump. 

[myk]

I'd still try to verify that the oil pressure is in fact down.  The chance of both your idiot lights and gauges being wrong is improbable but still easier than tearing into the motor right away...

[JB400]

I agree.  I'd install an aftermarket oil guage, and see where your pressure is at.  What viscosity of oil are you using?  Any additives?

[BSB67]

Having a lifter come out of its bore could give this symptom, but you usually lose a cylinder and should have seen it when you looked at the rockers.

If the motor was running fine otherwise, I would guess that the problem is someplace between the oil pan and the filter.  Look at the pump's pressure relief valve and rotor, although I've never heard of them slipping on the shaft.  Not in the pump, then the pick-up could be loose, cracked or broken.  That I have seen more than once.

[deepockets]

Like BSB67 said, I had the same thing happen and the relief piston in the oil pump was stuck in an open position. I removed it and sanded a smooth edge at the top of the piston. Problem solved and never happened again. Good luck regardless.

[John_Kunkel]

If the pressure was 75 psi at cruise, chances are the relief valve was wide open anyway.

[dstryr]

Guys, thanks for the replies...garage is pretty well packed for the winter but I may be able to get in there and under the car...do not want to wait for spring. 

BTW, the gauge is a mechanical aftermarket gauge running off a separate sending unit from the idiot light...so to have both fail on the same trip, can't see it.  And forgot to mention when turning over with valve cover off and oil cold, did not flood the garage floor with oil which would have happened if oil were getting up top normally...damhik.

[69wannabe]

Pull both valve covers and look to see if maybe a pushrod is gone and a lifter jumped out of it's bore like said above. I had a 440 wear down a cam lobe just slightly and it caused the pushrod to bend and pop out and let the lifter pop out of it's bore then the oil pressure went down to nothing. Also one time my buddy built his 440 and didn't tighten the oil pump screen into the block tight enough and over time it got lose and twisted up away from the oil pan sump and it wasn't pulling oil anymore. Let us know your findings!!!!

[RallyeMike]

Pull both valve covers and look to see if maybe a pushrod is gone and a lifter jumped out of it's bore like said above. I had a 440 wear down a cam lobe just slightly and it caused the pushrod to bend and pop out and let the lifter pop out of it's bore then the oil pressure went down to nothing.

From what I read here there IS oil pressure just not as much. It is therefore NOT a lifter out of the bore as pressure would be zero.

Best best is oil pump or partially blocked pickup screen.

[ws23rt]

I will step out on a limb and say the oil pump rotors are now groovy.

[BSB67]

Pull both valve covers and look to see if maybe a pushrod is gone and a lifter jumped out of it's bore like said above. I had a 440 wear down a cam lobe just slightly and it caused the pushrod to bend and pop out and let the lifter pop out of it's bore then the oil pressure went down to nothing.

From what I read here there IS oil pressure just not as much. It is therefore NOT a lifter out of the bore as pressure would be zero.

Best best is oil pump or partially blocked pickup screen.

It depends on which one.

But if it lost pressure gradually and the pushrods are all intact, it is not the problem..

[69wannabe]

I hate to admit this but I swapped intakes on a 440 one time several years back and left a rag in the lifter valley and it ran for a bit then the oil pressure dropped off and when I drained the oil and changed the filter I kept noticing little lint balls, well after we started it back up it had good oil pressure for just a few mins then low again. I decided to pull the intake since it was fine before I did the intake swap and there was pieces of the rag wrapped around the cam and the rest of the rag was sucked up to the oil pump screen!! Well out the engine came and had to go through it and clean out all the blue rag that was everywhere. After all that was cleaned out and several new rod bearings all was well again!! Live and learn!! 

[TXcharger70]

What should be the normal oil pressure @ operating temp? My stroker (496) 383 with hv oil pump runs around 20psi @ idle and 70-75 at 3000rpm. Cold @ idle is 80psi

[BSB67]

What should be the normal oil pressure @ operating temp? My stroker (496) 383 with hv oil pump runs around 20psi @ idle and 70-75 at 3000rpm. Cold @ idle is 80psi

Too many variables.  Bearing type, bearing clearance, lifter style, lifter clearance, oil weight, , to name a few.

I assume that even with the slightest throttle the pressure jumps.  If so, your good.

[TXcharger70]

I am using vr1 15 40.
Dstryr what oil weight are you using just as a curiosity?

[red69superbee]

i had sorta the same thing happen on a new engine,oil pressure was low to nothing.. ended up cranking the engine over a bit with the filter off just to make sure pressure was there.after that it was fine.may sound silly but that fixed me

[dstryr]

...and the pickup tube was cracked at the block and is now in my hand, minus 3/8"  of it still in he block

Glad its spring time so I could get into the garage and mess around with this again.  Anyway, there are no marks on the tube from it contacting anything internally so what causes this to happen?  Bad luck?  Maybe the assembler tried bending the tube to adjust for clearance? 

[BSB67]

.....then the pick-up could be loose, cracked or broken.

Vibration, and/or the pick-up too tight against the oil pan.  Is it original stuff or replacement pick-up and/or newer replacement pan?  For a bunch of years, the new pick-up for the Hemi pan was too long.

[dstryr]

It is a Source deep pan and pickup and no indication of contact of the tube and pickup with the pan or internals.  I'm betting on vibration as the cause.

[dstryr]

The oil pump is a melling high volume pump and at idle to cruise the pressure is 35-75lbs with 10W40.  Is that a good range?
Thought I'd ask while I'm ordering parts.