Intermittent Oil Pressure Fluctuations/drops to zero - 2001 5.3 in a Z71

[jocko]

I have an odd problem, thought I would tap into the experience on this board. I normally live in the 67-72 world, but my dd is a 2001 Z71 with a 5.3 with 242k mi - I realize "it's about time", ha....

So, here is the observation:
85% of the time, the oil pressure reading is dead nuts normal. Just like it has been for its whole life.

15% of the time, the oil pressure registers significantly lower, approx. 15 psi, and at a stop in Drive (the lowest I should ever see), it drops towards zero psi and triggers the oil pressure warning on the bright yellow message center.

Then, next time I drive it: Normal.

Maddening, eh?

Anyway, my research thus far leads me to believe it's probably some muck/blockage in the little metal screen in the passage that leads to the oil pressure sender. Have read of lots of instances of this being clogged and causing a false reading. But, I had one of the 15% occurrences today and noted that even if I rev'ed the motor, the max psi I'd see was about 20 (no load). It would very likely be fine if I drove it (which I've had to do thus far) with a load on the engine in drive - experience would lead me to believe this anyway. It SEEMS that if the pump were "going" bad, it wouldn't be "good" the next day, it would just get worse. But it would also seem that the likelihood of a clogged screen or sump pickup getting clogged and then getting better, over and over, is a stretch also.. HOWEVER, lately, the 15% is rapidly becoming 30% of the time - so I have a few questions:

1) Can the oil pump in an 01 5.3 "gracefully" degrade? In other words - can it have lower oil pressure one day and normal the next? My experience with older mech pumps is that they go from working to not working and that's it. Aside from a clogged screen in the old style pickups, it was a 1 or a 0, workie/no workie - so am curious to hear who's lost a pump and the symptoms you may recall leading up to it.

2) Is the screen the likely culprit? Has anyone had the sump screen clog?

3) If it IS the little screen before the oil pressure sender that is clogged - does a clog there inhibit oil flow throughout the engine or does it only inhibit oil flow to the sender? (I assume the latter - but this has been a burning question I've had - and may directly affect whether or not I harm my engine when these symptoms pop up)

4) Any other ideas as to what these indications could mean are welcome.

I've been milking this problem because it's been self-healing thus far. Time to address, and no time to experiment in a piecemeal fashion. If it's going down for maint, gotta get it solved (sound familiar)? Ha.

[izzy_Britton]

Since no one else has responded, let me take a stab at this for you. First let me lead by saying that i am no expert. I would still consider myself new to this model engine and the LS of things in general. But i am a hands on guy and have learned a ton over the past couple years. this is obviously not gospel but seems perfectly logical to me.

Originally Posted by jocko

... dd is a 2001 Z71 with a 5.3 with 242k mi - I realize "it's about time", ha....

YES, is about time for your typical small block to cease functioning properly, but i have seen some of these engines go for 400k, much longer than the truck itself is good for. I bought a burb with 220k and the thing look like it was built for the first time last week, you could still see the cylinder hone marks. it all depends upon maintenance. on the flip side of that scale i have one that has less than 80k on it and it is so gunked up inside, it will require a complete rebuild before it sees life again. so yeah, maintenance is the key, it is your DD so you should know where you stand in that dept.

Anyway, my research thus far leads me to believe it's probably some muck/blockage in the little metal screen in the passage that leads to the oil pressure sender. Have read of lots of instances of this being clogged and causing a false reading. But, I had one of the 15% occurrences today and noted that even if I rev'ed the motor, the max psi I'd see was about 20 (no load). It would very likely be fine if I drove it (which I've had to do thus far) with a load on the engine in drive - experience would lead me to believe this anyway. It SEEMS that if the pump were "going" bad, it wouldn't be "good" the next day, it would just get worse. But it would also seem that the likelihood of a clogged screen or sump pickup getting clogged and then getting better, over and over, is a stretch also..

yes and no, I have a story at the end to tell you about this almost exact thing. kinda funny too.

HOWEVER, lately, the 15% is rapidly becoming 30% of the time - so I have a few questions:

1) Can the oil pump in an 01 5.3 "gracefully" degrade? In other words - can it have lower oil pressure one day and normal the next? My experience with older mech pumps is that they go from working to not working and that's it. Aside from a clogged screen in the old style pickups, it was a 1 or a 0, workie/no workie - so am curious to hear who's lost a pump and the symptoms you may recall leading up to it.

yes an oil pump can gracefully degrade, but they degrade, and NOT heal themselves overnight, in the LS style engines, they can degrade from working to not working and they are dead, being crank driven they are a totally different animal than the typical SBC.

2) Is the screen the likely culprit? Has anyone had the sump screen clog?

LIKELY yes I just recently learned about this screen, I was chattering on another thread somewhere about changing out some parts on my wifes truck and changing out the oil pressure sending unit and someone spoke up and told me about the screen. my screen was lightly gunked, I think i still have it on the work bench, if i can remember i will snap a photo of it and post it later in the weekend.

3) If it IS the little screen before the oil pressure sender that is clogged - does a clog there inhibit oil flow throughout the engine or does it only inhibit oil flow to the sender? (I assume the latter - but this has been a burning question I've had - and may directly affect whether or not I harm my engine when these symptoms pop up)

I dont know for sure. when i tool my engine apart for my LS swap it appeared that oil went everywhere and there was only a passage to the sender, but i didnt really look all that hard at it.

4) Any other ideas as to what these indications could mean are welcome.

I've been milking this problem because it's been self-healing thus far. Time to address, and no time to experiment in a piecemeal fashion. If it's going down for maint, gotta get it solved (sound familiar)? Ha.

SO now for my take on your issue. not exactly the same but i think it is a logical explanation of what could be happening under the circumstances.

20 years ago i was working at small repair shop. this little old lady drove her ford taurus into us because she was having intermittent loss of power issues. as the car was having one of those issues she happened to be driving by and pulled into the lot, not quite making it all the way to the shop because of the loss of power, but the car was still running. being young, i jumped to the logical conclusion that the fuel pump was intermittently crapping out.

ma'am can you shut the engine off? she did and i smacked the bottom of the tank a couple times with a rubber mallet. she started the car, revved it to the moon a few times, all was good, explained she would need a fuel pump soon or she will be stranded on the side of the road, off she went.

a few days later she was back. same thing. again smack the bottom of the tank and off she went. and again a few days later she was back... the boomerang that we all love to hate. i chatted with my boss and we came to the conclusion that there was no way around it, the fuel pump needed to be replaced. But the little old lady was short on funds so just to make sure, i just ended up replacing the fuel filter. she fired it up, revved it to the moon and off she went again.

about 2 or 3 weeks went by and low and behold the little old lady was back. this time she wanted to replace the fuel pump. I dropped the tank, changed the fuel pump, test drove it, she picked it up and off she went.

just like little carol-anne.... she's baaaaack... same issue. this time we kept her car for a week or so. i drove it home and to chase parts and sure as hell it did its thing while i was driving it. I limped it back to the shop, while it was still running we checked fuel pressure and it was way low. dumb fuel pump must be defective. we changed fuel pump again. i drove it for a few days without issue and she drove it home.

then she drove it back. this is really one of those issues where you want to just push the car into the street and light it on fire... yes i am getting to the point. one more sec.

low fuel pressure must be a pump, pulled the tank for the 3rd pump install, I dont know why i did it but i completely drained the tank while it was out. we had only ever drained enough fuel out of it as necessary to change the pump and never really looked inside the tank, i mean never REALLY looked. we peered in the tank before and it was nice and clean, why investigate any further? right? anyways this time i drained it and cleaned the inside of the tank. upon draining the tank we hadnt noticed anything out of the ordinary. after changing the pump again, we dumped all her fuel back in the tank filtering it thru a makeshift filter. after the funnel clogged up we knew something was amiss. sure as $#!T. we found the thing that was likely the problem all along.

somehow someway someone had gotten a cellophane cigarette package wrapper into her fuel tank. being clear as they are we couldnt see it at all in the fuel. but what we figured was that the wrapper was floating around in the tank and once in a while it would get stuck on the pickup filter causing a partial blockage and thus causing low fuel pressure and the problem of loss of power. by turning the engine off the wrapper would dislodge itself from the pickup filter and the car would run fine until it found the filter again.

the little old lady never came back. so i know its a long story but the point is, if there is a 'flake' of grunge and it is lodging itself against that sending unit screen causing a low oil pressure situation, and then the engine is stopped and the flake falls or moves, MAYBE it would read normal next time you run the engine and, again when you stop the engine the flake moves and partially blocks the screen again on next startup?

I would guess this is possible for EITHER the sending unit screen or the pickup screen in the oil pan.

there is an easy way to check, well maybe not so easy as it might seem but a possible temp solution?

get a mechanical oil pressure gauge (35$ at parts store) and a sump plate threaded to accept the oil line and rest the gauge in the engine compartment, when you have one of those low pressure moments you can verify if it is indeed the sending unit screen or not.

ok, all done with my lame explanation and thoughts. good luck, let us know what you find out and hopefully if i am way off someone will speak up.

Happy Thanksgiving

-Izzy

[jocko]

Hey thanks a lot Izzy, appreciate your thoughts on this. Yes, have owned since new and changed the oil at every 3K even if overkill, so that's why I don't want to inadvertently throw away 17 years of careful maint over a bad pump - but also don't want to waste the time and $ in installing a new one if it's not the real problem. Your fuel story is my underlying concern - I'd suspect that more than a failing pump for sure, but I don't smoke so hopefully nobody else stuffed cig cellophane in my oil system! Wouldn't surprise me at all at at least some of the dealerships I've been to. And I also would not expect a crank driven pump like this to go bad and then be ok, but I'm not as familiar with LS motors as older chev motors, so wanted to ask. Only makes sense though. Anyway, the plan of attack is to replace the sender screen and see what happens. Could be a $5 fix and that's it. If pressure is restored to normal and it remains that way for more than a week, I'm going to feel pretty comfortable that that was the culprit. Thanks again for your time!

Btw, for anyone interested, here is a picture of the part I'm talking about - GM Part # is 12585328 - costs about $5-7.

[izzy_Britton]

the only problem that i see is that it is a real PITA to get your hand back behind the intake manifold to R&R that part. but in this case patience is a virtue. lol

-Izzy

[izzy_Britton]

I looked for MY oil screen so i could get a photo of it for you. I must have tossed it when cleaning up. for fun i pulled the sending unit out of another engine so i could check that screen, and that engine doesnt/didnt have a screen installed. I assume it was never installed from the factory. odd.

-Izzy

[95 S_Trucker]

The only engines I have seen a screw in is on the afm motors.