Low oil pressure on acceleration

[phatz_hatz]

I have a 95 Tahoe with the TBI 5.7 in it, has 227,000 miles on it 10w30 in it and a quart of Lucas oil. Yesterday i realized that when starting from a complete stop the gauge dips down pretty low below 20 but once i get it going again it reads 30-40. I’m wondering if it is more likely the sender unit or the oil pump itself. Truck runs fine and at idle it idles at 20 psi. Just everytime i accelerate from a dead stop it drops then builds back up again. Don’t wanna starve the engine of oil considering it’s age and mileage. Any help would be appreciated !

 

[B-train]

My advise would be to hook up a mechanical guage and tape it to the windshield and to a test drive. If the guage agrees with what you saw, then you have internal issues to look for - possibly a tired pump or worn bearings

 

[phatz_hatz]

My advise would be to hook up a mechanical guage and tape it to the windshield and to a test drive. If the guage agrees with what you saw, then you have internal issues to look for - possibly a tired pump or worn bearings

If it is the bearings would a high volume pump help supplement the space created due to them being worn ?

 

[B-train]

Probably would help, or just try 1 grade thicker like a 10w-40 or a 5w-40 oil and see how it acts.

 

[strutaeng]

It's not low on oil? I've got a 5.7 Vortec 2000 OBS K3500 CCLB SRW. She's a weekender work truck I rarely use and was a former ranch truck, I.e., rough around the edges. I know it leaks oil...from a lot of places. It's an oily mess down there.

Anyways mine started doing what your described and it turned out it was just low on oil! Doh! Mine actually dipped to around zero on the garage (which is not actually calibrated to numerically to "psi" if you didn't know.)

 

[OR VietVet]

The idle reading is not bad and neither is the accel reading. The dip concerns me though. Additives, different weight oil....maybe. Best is to deal with a mechanical gauge, like @B-train said, and know for sure. Or just attempt the additives, oil and/or new sender route. I am assuming no noises. At that mileage....who knows....

 

[phatz_hatz]

Probably would help, or just try 1 grade thicker like a 10w-40 or a 5w-40 oil and see how it acts.

Thank you, will try over this weekend and see what happens

 

[phatz_hatz]

The idle reading is not bad and neither is the accel reading. The dip concerns me though. Additives, different weight oil....maybe. Best is to deal with a mechanical gauge, like @B-train said, and know for sure. Or just attempt the additives, oil and/or new sender route. I am assuming no noises. At that mileage....who knows....

No noises, it had a slight lifter tick yesterday but once i let it idle for a while it went away cause the oil pressure was fine. So it was getting up there again. Truck runs really good for the mileage.

 

[phatz_hatz]

It's not low on oil? I've got a 5.7 Vortec 2000 OBS K3500 CCLB SRW. She's a weekender work truck I rarely use and was a former ranch truck, I.e., rough around the edges. I know it leaks oil...from a lot of places. It's an oily mess down there.

Anyways mine started doing what your described and it turned out it was just low on oil! Doh! Mine actually dipped to around zero on the garage (which is not actually calibrated to numerically to "psi" if you didn't know.)

I’m not sure honestly i don’t see any leaks on the pavement where i park. Under the hood tho is a different story, but I’m not sure if it’s oil or power steering fluid that’s built up or both lol. I will check the oil when i get home from work. I have a van for work that i drive home so that’s a plus if i gotta put her out of commission for a lil

 

[OR VietVet]

I’m not sure honestly i don’t see any leaks on the pavement where i park. Under the hood tho is a different story, but I’m not sure if it’s oil or power steering fluid that’s built up or both lol. I will check the oil when i get home from work. I have a van for work that i drive home so that’s a plus if i gotta put her out of commission for a lil

Gotta remember that each system has it's blood that it needs. Engine=oil. Engine=coolant. Brake system=brake fluid. Power steering=p/s fluid. Transmission=transmission fluid. Transfer case=transfer case fluid. Front and rear differentials=differential fluids. Windshield=washer fluid. You get the picture.

 

[strutaeng]

For sure try to find the leaks and fix them.

I wouldn't be too concerned about the oil pressure. I think mine idles at "20" on the cluster hot idle on my K3500.

When the 4.3 Vortec was dying on my 99 Silverado, at hot idle during the summer my gauges dipped below zero on the cluster and the "check gauges" light would came on. Truck had around 260k.

I hooked up a mechanical guage and revving up the engine actually still met spec, surprisingly. At idle I had 5 psi. I didn't have money to fix it because I was in the middle of a large home addition. I switched to the heaviest oil they sell. Pressure increased another 2-3 psi. I ran it like another 10k miles until I retired it. Engine never made any knocking or noises. I eventually swapped a 5.3/4L80e and truck still lives.

 

[Hoesgottaeat2]

Keep in mind these gauges are known to become less and less accurate over time. And sometimes they even start to bounce all over the place.
I agree with comparing with another aftermarket gauge.
General rule I was always taught was…
10psi oil pressure per 1000rpm of engine speed. Minimum for proper lubrication. Sounds like you’re still in the safe range according to your findings. I’d still check with an aftermarket gauge myself. Small price to pay for peace of mind IMO.