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The oil pressure sender screens are notorious for clogging..
They sell a gadget that allows 2 bolts to hold the pickup tube in place. I used one it fit well and made the tube feel like it was welded in.. I believe it was a ICT part..
Oil pressure gauge port is a dead end - might some blockage in that channel. Try removing the sending unit and starting the car should be a fountain of oil.
I believe you are chasing ghosts / a non problem!!
How many times do you hit the rev limiter?? Neutral Drops?? Smoke the tires?? Is this car beat on?? Previous owner did smokey burnouts all the time??
Yes I have experience with 5.3L having low oil pressure but 230,000 miles.
Your oil sending unit passage got some crap in it causing bad gauge readings.
Great comments. I know a retired mechanic who spent his career on Gen 1 small blocks who is essentially saying the same thing. He believes if the internal pressures were really that low, it would be making some awful noises and just plain groaning with displeasure. This engine purrs like a kitten no matter the rpm’s. This is a nice weather weekend cruiser for my wife and I to make ice cream runs. The only time I ever get above 2K rpm’s is when the auto tranny is going from 1-2.
I will try purging the sensor port - probably going to make a mess, but what the hell.
The oil pressure sender screens are notorious for clogging..
They sell a gadget that allows 2 bolts to hold the pickup tube in place. I used one it fit well and made the tube feel like it was welded in.. I believe it was a ICT part..
The early LS engines did not have an oil pressure sender screens. The later Tahoes and Suburbans did.
The little gadget - is that the little crow-foot that secures the oil sump tube into the oil pump? Improved Racing makes one.
The early LS engines did not have an oil pressure sender screens. The later Tahoes and Suburbans did.
The little gadget - is that the little crow-foot that secures the oil sump tube into the oil pump? Improved Racing makes one.
I forgot it was a interim part, but the senders are also known for plugging.. , but I know of more than one person who didn't know the screen could be there, they come in the box with the sender and some install them thinking they are an "improvement" whether its the right year or not..
yes ts a little half moon gadget that uses the original bolt plus wraps around the tube and uses one of the other bolts to double down on holding the tube and o-ring in place..
First time I ever saw in side a LS family engine I thought " why the hell is there only one bolt? and on top of that it pulls diagonally on the o-ring seal.
The extra support is pretty obvious when you look at how it clamps the tube and o-ring in to the pump. Made me feel better.. Even if its a placebo.
I have not measured oil pressure at the port on the front of the block, but I have measured it at the oil temperature sensor port, and the difference between there and the sensor location was 3 psi across the board at operating temperature (about 190 degF). Being that the port you're measuring from is nearly a straight shot from the oil temperature sensor location, I can't imagine the difference being much greater, probably within 1 psi or so - meaning that the drop from the front port to the sensor port should be ~4-5 psi.
I had a low oil pressure problem on an LS6 (hence my measuring it) and it turned out to be a walked #1 cam bearing. I would routinely hit 7-8 psi on the dash at 200+ degF oil temperatures. So, it's likely that your engine may have the same problem with that much oil pressure at idle.
Did your engine show any other signs of a problem from the bearing slide? Knocking, squealing, irregular idle from a wabbling cam, etc? Mine is showing no signs of any problems other than low oil pressure.
Also, when you replaced the bearing, did you have to go back with an oversized bearing?
I am about to pull the intake (third time), pull the knock sensor plate, and try to view as many cam bearings as I can with my little camera probe.
Oil pressure gauge port is a dead end - might some blockage in that channel. Try removing the sending unit and starting the car should be a fountain of oil.
I believe you are chasing ghosts / a non problem!!
How many times do you hit the rev limiter?? Neutral Drops?? Smoke the tires?? Is this car beat on?? Previous owner did smokey burnouts all the time??
Yes I have experience with 5.3L having low oil pressure but 230,000 miles.
Your oil sending unit passage got some crap in it causing bad gauge readings.
Not only that, the OEM senders are on nobody's list for accuracy and reliability. Accuracy and reliability are on par with an ex-wifes testimony at a custody hearing!! Last sender I installed was purchased at O'Reillys in my C5 4 or 5 years ago. Not the lifetime guaranteed one, either. No leaks, and pretty accurate when compared to a manual gauge. It got old seeing 130lb readings every 3 or 4 years. It REALLY got old-QUICKLY-Seeing a 0lbs reading, not to mention stroke risk due to ultra high blood pressure!!! DONT BUY THE OEM SENDER!!!!
Thank you for the response. Plan A is tempting, but the “ignorance-is-bliss” ship has sailed on this one. My skin is crawling when the pressure gets down to 11ish.
Plan B: Yes. Right now, the engine starts and runs smooth as jazz music. No strange noises, no knocks, no squeals, no oil consumption. If I have some internal problem, I want to minimize the damage for whoever ends up rebuilding the engine. I have it for sale as-is over at the Corvette Forum. No takers yet, so I may end up rebuilding this engine (gonna take me a year or two, gasoline will be contraband by the time I get done).
The advice you guys are giving me is a huge benefit.
After changing the oil pump and sump o-ring, I primed the pump using the Melling method of flowing oil directly into the pump from the small port on the oil galley on the lower front driver side of the engine. After running the engine and observing low pressure (initially 15ish down to below 10 and getting warning messages) at the instrument cluster gauge, I eventually obtained a Snap-On brand mechanical oil pressure gauge kit from my mechanic friend. I used one of the adapters to connect the gauge at the upper firewall sensor location (removed electric sensor) and verified the instrument gauge as accurate.
I then reconnected the sensor and moved the mechanical gauge to the oil pump priming port on the lower front drivers side of the block where Melling says to prime the pump. I connected the Snap-On gauge using one of the supplied adapters. No pictures. This port is directly off the oil pump approx two inches from the oil pump discharge port.
My pressures at the oil pump on a cold engine running Royal Purple 5w-20 were mid-30’s to lower 20’s for the 30 seconds I ran the engine on multiple crankings. Ambient temps in the 50’s. Car on jackstands, no water pump, no drive belt. Harmonic balancer installed. I kept the rpm’s below 1200. The instrument gauge was simultaneously showing mid-to-low teens of oil pressure then slowly dropping to ten when I shut it down. I had a pressure difference of about 20 psi from oil pump gauge to oil pressure sensor.
I have now completely re-assembled the engine including coolant.
Yesterday, I changed the oil and filter using heavier Castrol 20w-50 and a new Wix filter. The highest pressure I got at the instrument panel gauge was 18psi then it slowly crept down to 10 psi as the engine warmed up when I shut it down. I don’t have the Snap-On gauge anymore. Based on my earlier observations, I am assuming the pressure off the pump is 15-20psi higher (25-40 psi) but I am not sure. Even those pressures, if my assumption is accurate, are not impressive for heavy cold oil.
While I had the oil filter off, I checked the Oil Filter Bypass valve using a small screwdriver. It was springing open-closed smoothly. I pressed it up numerous times and it closed smoothly. It appears to be functioning.
I did not connect the Snap-On gauge anywhere else. Even though I am disappointed in the low pressure coming directly off the oil pump, I could still live with pressure in the mid-20 to 30 range for a short time. However, I don’t understand the sharp drop in pressure from the oil pump to the sensor of about 15-20 psi differential.
Is there another port that will provide a more accurate reading of internal pressures where they really matter? Surely, GM placed the firewall pressure sensor and calibrated it to provide us with a meaningful pressure reading?
I'm wondering why you were running 5w-20 oil?? That said, if you're connected at the drivers side main port, just a few inches from the pump itself, and are only reading 20-30lbs cold pressure, you have a serious problem, and it doesn't matter whats going on at the factory sender port up top!! Either your oil pump relief spring is bad, the relief valve is stuck, the pump itself is bad, O-Ring is leaking, pump screen is plugged, pickup tube is somehow cracked, or you have bearing/lifter issues. When I connected a mechanical gauge to the front port (pre-filter pressure), my engine had 60lbs cold at idle using 0w-40 oil. When hot, this port read 5-7lbs more pressure than the top OEM sender port (after filter) did. Hope this helps..
I'm wondering why you were running 5w-20 oil?? That said, if you're connected at the drivers side main port, just a few inches from the pump itself, and are only reading 20-30lbs cold pressure, you have a serious problem, and it doesn't matter whats going on at the factory sender port up top!! Either your oil pump relief spring is bad, the relief valve is stuck, the pump itself is bad, O-Ring is leaking, pump screen is plugged, pickup tube is somehow cracked, or you have bearing/lifter issues. When I connected a mechanical gauge to the front port (pre-filter pressure), my engine had 60lbs cold at idle using 0w-40 oil. When hot, this port read 5-7lbs more pressure than the top OEM sender port (after filter) did. Hope this helps..
Yes. It helps my decision process. The oil pump is a new Melling M295 standard volume with a new (correct) o-ring. The pressure ranges from upper 30s to lower 20s. That is why it seems all indicators point to a plugged sump screen or walked-cam bearing. Before I pull the engine (no simple task) or sell the car for nothing, I just would like to be sure. I will probably just end up pulling engine.
Yes. It helps my decision process. The oil pump is a new Melling M295 standard volume with a new (correct) o-ring. The pressure ranges from upper 30s to lower 20s. That is why it seems all indicators point to a plugged sump screen or walked-cam bearing. Before I pull the engine (no simple task) or sell the car for nothing, I just would like to be sure. I will probably just end up pulling engine.
You may remember my earlier post about my rearmost cam bearing walking forward. When this happened, it walked far enough to completely uncover the oil feed hole. Went from 50lbs to 0 in 30 feet!! When I pulled the motor, most of the bearing was sticking out of the journal. I have heard some very knowledgeable LS builders say the aluminum blocks are good for 3 or 4 cam bearing changes. After that, they've told me they feel the bearing journals have worn ever so slightly enough that the bearings no longer have sufficient crush/press to keep them in the assembled location. I'll say this; next aluminum block build I do, I'm staking the bearings.
You may remember my earlier post about my rearmost cam bearing walking forward. When this happened, it walked far enough to completely uncover the oil feed hole. Went from 50lbs to 0 in 30 feet!! When I pulled the motor, most of the bearing was sticking out of the journal. I have heard some very knowledgeable LS builders say the aluminum blocks are good for 3 or 4 cam bearing changes. After that, they've told me they feel the bearing journals have worn ever so slightly enough that the bearings no longer have sufficient crush/press to keep them in the assembled location. I'll say this; next aluminum block build I do, I'm staking the bearings.
So you went back with original sized cam bearings when you replaced yours? Any work done to the block by a machine shop?
If I can pull the motor and get away with only replacing gaskets and bearing inserts in the cam, rods, and crank, then I may go ahead and do this. I just don’t have the cash to make a $6000 plus project for a car I rarely drive.
So you went back with original sized cam bearings when you replaced yours? Any work done to the block by a machine shop?
If I can pull the motor and get away with only replacing gaskets and bearing inserts in the cam, rods, and crank, then I may go ahead and do this. I just don’t have the cash to make a $6000 plus project for a car I rarely drive.
Yes, OEM size. It was a '98 block. Bought used. Could've been the 4th or 5th rebuild, who knows. Block had Darton sleeves in it. Worked great for 30,000 miles. After this happened, I sold the block. Like I said, if I ever put cam bearings in another aluminum block, they'll be staked-On both sides.
Yes, OEM size. It was a '98 block. Bought used. Could've been the 4th or 5th rebuild, who knows. Block had Darton sleeves in it. Worked great for 30,000 miles. After this happened, I sold the block. Like I said, if I ever put cam bearings in another aluminum block, they'll be staked-On both sides.
Ok. I can use some recommendations on brand of cam bearings.
Also, did you consider using Red Loctite or something similar when inserting?
You are going to buy cam bearings w/o knowing that's the problem?
Does your C5 have a 2-piece oil pan? My 2000 does. If so, it's easy to take the bottom off and check the pickup screen.
You are going to buy cam bearings w/o knowing that's the problem?
Does your C5 have a 2-piece oil pan? My 2000 does. If so, it's easy to take the bottom off and check the pickup screen.
“You are going to buy cam bearings w/o knowing that's the problem?“
No. Of course not. Why would you think that? Since I have to do something with or to the car, I am pricing possibilities for budgeting purposes. Need brands/models/etc to price parts. I am sure you do the same thing.
The 99 has a one piece pan. Dropping the pan requires dropping the cradle and supporting the engine with a hoist. Real PIA.
Ok. I can use some recommendations on brand of cam bearings.
Also, did you consider using Red Loctite or something similar when inserting?
No, never considered loctite, because I never heard of this happening before. If anyone is considering loctite, Id recommend the blue #242 (?), not red. Like I said, if I ever do another aluminum block, cam bearings will get staked, on both ends where possible. Problem solved.
I am aware that publications say 10 psi per 1000 rpm so 6 psi at idle is "normal" That's pure BS.
Everything I've ever seen with less than 18 psi oil pressure at idle and less than 40 psi max hot has had a mechanical problem.
Your pickup screen is not plugged (unless someone dropped the oil bottle seal in the engine and it somehow made it's way to the pan)
What is the pickup screen going to be plugged with at 76,000 miles?
Oil filter bypass stuck open? It's going to bypass the oil filter, if anything that will raise the pressure.
And whatever you do please don't take it out and replace it or send it out for a rebuild. Find the problem, then have it fixed. This is how we all learn.
02-14-2023 | 01:38 PM
Even if its a placebo. 
Last sender I installed was purchased at O'Reillys in my C5 4 or 5 years ago. Not the lifetime guaranteed one, either. No leaks, and pretty accurate when compared to a manual gauge. It got old seeing 130lb readings every 3 or 4 years. It REALLY got old-QUICKLY-Seeing a 0lbs reading, not to mention stroke risk due to ultra high blood pressure!!! DONT BUY THE OEM SENDER!!!! 
