DWA_99

I have been over at the Corvette Forum for a few years. I am looking for some LS technical knowledge that it appears is not available over there. I am asking here.

1999 Corvette Convertible, stock LS1, automatic transmission.

Sorry for the long message below. I ask a technical question at the end, but need to give the background first.

I have enjoyed my 99 Vert for a couple of years. It runs great. Has given me no problems.

I recently discovered it has low oil pressure. I really do not have time or money to tear the motor out and down, so if I can’t solve this issue without pulling the motor, I will sell the car as is.

When I bought it, the oil pressure gauge was pegged as so many of these things are. I have run it from Louisiana to Georgia and to Texas and back like that with no issues or strange engine sounds.
A few weeks ago, I finally had time to pull the manifold and replace the sensor.

On test, I discovered my oil pressure at the firewall sensor was running 15 or less on cold start then dropped to below 10 as it warmed up. I then got “Low Oil Presure” warnings and shut it down. It remained above the GM spec of 6 at idle.
Fast forward much work (new sump oring and oil pump) and checks to now where I have been comparing readings from the Oil Pump Priming Port located on the Drivers Side at the front bottom of the block directly off the oil galley using a Snap On mechanical oil pressure gauge. I get readings of mid-twenties up to upper-thirties of pressure while only getting 15 or less at the (confirmed accurate) sensor up on the firewall.
I have yet to confirm my sump screen is not plugged, but don’t have time to drop the pan - major pain.
My question: I understand the oiling system is not “closed” like a braking system is. A brake system will keep equal pressure throughout with a non-compressible liquid and no “exit points.” As pressurized system open in the end, with the engine oiling system, Inwould expect some pressure drop from the initial pump to the very end of the system (near the gauge) until the oil finally exits the pressurized portion and falls into the oil pan.
I have tried to research to verify this, but haven’t had any success. With a healthy LS engine, has anyone ever gauged pressure from the pump to the sensor to determine if there is a pressure drop? If so, what were the readings?
The standard Melling M295 pressure relief valve is set to 70psi. We typically get 40ish at the gauge. Given if there is a 20ish psi drop across the system, I may be seeing symptoms of a plugged oil sump screen. If that is the case, it may be worthwhile for me to justify pulling the pan, and checking the sump.
I would like to keep my beauty, if I can do it without dumping a fortune (more) into it. Any insight would be appreciated.

Che70velle

iTrader: (6)

Welcome to LS1Tech. Sounds like she’s a driver…lots of miles? Have you ever cut open your oil filter (with the correct $40 tool) to look for bearing debris? What do your oil temps look like? There’s not going to be a pressure drop between the pump and the sensor, because the sensor is in line BEFORE the lifters and bearings, which dictate the pressure. Rod bearings are last in line. Main bearings are in front of rod bearings. Lifters (lifter body to lifter bore clearance) are first to oil followed by cam bearings. Any one of these being worn can cause an oil pressure issue. I see cam bearings walk out of their bore fairly often, so that’s suspect number one. Start with cutting an oil filter open and inspect for debris. How do your cruising oil pressures look?

DWA_99

Thank you for the response. I am not familiar with the inside routing of the oil. That is good information.
Also, I have read about number 2 or 3 bearing walking out on the early LS engines. I am hoping that is not the problem because I will be selling the car if so.
As far as temps and pressure before this discovery, I do not know. I purchased the car with a bad sensor and just got around to changing it. This may be recent or it could have been like this when I got it. I do have dealer service records up to 65000 miles and there is no mention of any issues. It currently has 76000 miles. I have put just over 3000 on the car (I rarely drive it.)
I will pull the filter, drain the oil, and search it all for shavings or debris and report back. Note the engine sounds fine. No knocks, squeaks, banging, etc. Maybe a slight lifter tick.
Is it possible my Oil Filter Bypass is stuck open?
Is there a way to check that with the engine in the car, if that may be a possibility?
Once again, thank you.

DWA_99

This is why I would like to keep her.

SledgeHammerRacing

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.

stock48

iTrader: (17)

I've seen this on many LS engines and a lot of the time it has been the oil pump O ring sucking air. I usually instal a new Melling 295 pump and Oring and it fixes it. Like said above id cut the oil filter open and inspect it before tearing into it.
Edit I reread your 1st post and looks like you've already done this. But did you pull oil pan when you did it? It's really hard change oring and oil pump without jacking oring up with pan on. I've also had oil filters break down and or clog and cause low oil psi.

DWA_99

Stock,
I was thinking like you and suspected the sump o-ring or the pump’s pressure relief valve initially, so I installed a new Melling M295 with the proper Melling o-ring that came with the kit. The old valve moved easily and the old oring did not look too bad. The new pump went on easily, and I am positive the new ring wasn’t pinched judging by the way it went together.

I am not sure about my sump screen. Since my pressure off the pump is low, about 25-35 with cold oil, is it possible my screen is varnished and gunky?
I bought this car from an older man who had double-knee replacement. It had not been run much at all for over a year.
Thank you for the input. I guess I will drain/evaluate the oil and filter and go ahead and drop the pan to check the sump. I believe I can see a few cam bearings when I drop the pan, correct?

Che70velle

iTrader: (6)

You'll have to remove the windage tray as well, but you can see a couple cam bearings from the angle you’ll be looking at behind the crossmember.

Guy with a Chevy

No one is going to tell him to run some 10-40 or 20-50 if need be should save it awhile while you think of a way to get it rebuilt. I'm novice could be the worst idea

DWA_99

The car is not my daily driver. I can leave it sitting for months, if need be. I have some left over AMSOIL Z-Rod 10w-30
from my 82 vette. It also has Zinc. I can drain and fill with the Z-Rod, if it will help me get a little pressure temporarily. Certainly easy to do right now because it is still on jack stands…What do you think?

Che70velle

iTrader: (6)

Nope. 30w is 30w from a viscosity perspective.

DWA_99

Good point. I guess I could throw some old Rotella I have for my diesel tractor in there!

Good suggestion. I will change to some 15w-40 and see what happens.

grinder11

iTrader: (1)

If it's the O-ring, a thicker oil will ever so slightly help the O-ring seal. I may have missed it, but was the pressure OK until the sender was changed? I've had them fail both ways, and at zero, you'll get a free heart stress test!! If it's an OEM sensor, it could be a bad sensor, even new. They're on nobody's list of reliable parts. The front port on the block is pressure before the filter, so it will read slightly higher, by maybe 5lbs(?). Best of luck.

grinder11

iTrader: (1)

Never mind. I agree with Scott. Doing exactly what mine did, but I lost all pressure. Cam bearing walking out, the last one@the rear of the block, happened to me. Instant Zero oil pressure!! I told myself if I ever do another aluminum block, I'm going to "stake" the cam bearings. Should be easy on aluminum. Sucks when that happens. Another great argument for priority main oiling....

Biebs

Might be a CAM bearing out of place -

Also try some engine cleaner run through the oil system. Motor flush, Automatic transmission fluid (lots of detergent), Diesel fuel mixed with oil.

Could be blockage and might get cleaned up.

Sounds like you change your own oil - do your notice old oil is very black??

Here is a post about how I Cleaned my engine internally and now oil stays nice and clear. Your car low mileage may suffer from gunk blocking the passages.


https://ls1tech.com/forums/generatio...ernal-car.html

Papermachtech

Plan A
Dam, put the old sensor back and drive it like you did. It's functioning isn't it?
Plan B
I know you want to avoid an expensive motor failure. I need to know how you connected the gauge at the oil filter port.
Some know issues there but need more information or a picture.

DWA_99

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?

DWA_99

“Sounds like you change your own oil - do your notice old oil is very black??“

Yes. I change my own oil. I can’t answer this question because I was using Royal Purple in my Corvettes until recently. As such, the oil is very dark when new.
I switched over to AMSOIL for my cars, so this will change.

I have read about some using Sea Foam in oil according to the bottle instructions. Apparently, Sea Foam can also serve as a cleaner. I have only the container label as my source. I have never felt the need to do it.

If I have a Walked-out cam bearing and the internals are only getting minimal oiling now, I may risk killing my engine by thinning the oil further. Opinion?

Biebs

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.

Guy with a Chevy

Does ^^^ happen often?