Low Oil Pressure on Longer Drives

[SnowDrifter]

okay, good. I now need to keep an eye on the rear axle. There is a whine (not loud) at 45-50mph. The noise is there at torque on and off. If held just neutral then the noise goes away. The axles were pulled out about 4? years ago and the wheel bearing inner races were not looking great - about 1/2 worn. There's always something.

Chuck some 75-140 in there and run 'er till the noise starts to snowball

Did that when my front diff was going out on account of the PO running it out of fluid. Got the better part of 40k out of it before I decided it was time for replacement

 

[2006Tahoe2WD]

I've thought of that but it seems sort of a cheat. This would avoid the fun of spending $1,500? on new axles.

 

[Jfarm]

All, I finally tested the truck on another 2 hour trip and have an update. Before I took it on the drive, I ran a camera into the oil pan and saw there was a little bit of sludge in the pan, not a lot, but some. I cleaned it out of the pan and put more oil in.

I took it on the two hour drive and again the oil pressure started strong at 65 psi but slowly dropped to 40psi in about 45-60 minutes. Right on the 40psi mark I got the lifter tick again. The oil continued to drop but held steady around 30psi.

Something different that happened on this trip, it was about an hour and a half in I got an engine misfire. I had a loss of power and the "check engine soon" light flashed a couple times. Five minutes after the check engine soon light turned on and stayed on but the next day it turned off. Additionally, later in the drive when the pressure was sitting around 30psi and I noticed that when I gave it a little gas, the pressure would drop 5-10 psi and when I let off it went back to 30psi.

Furthermore, after I got off the highway I stopped at a light and the pressure dropped from 30 down to 0. I shut the truck off and restarted it at the light and the pressure went to 35. Two minutes down the road the same thing happened. At the next light I put the truck into neutral and kept a little gas on it and the pressure stayed at 30.

This is such an odd issue as I will only have problems on the longer drives holding in the mid 70's at roughly 2000 rpm. After the truck cools down, the lifter tick goes away and pressure is perfect at 45-50 psi at idle and goes up to over 70 when I give it gas around town.

I took it to a different mechanic after the drive and he did several tests. To check the oil pressure, he let the truck idle for an hour and a half in front of the shop and then took the truck on a 40 minute drive driving around 55mph. He kept a manual oil pressure gauge on the whole time that tracked the pressure and the pressure the whole time was normal. He also scanned the codes and the memory bank showed P0300 random misfire detected, P0404 EGR feedback signal out of range, P0443 EVAP Purge control circuit fault, and P1133 HO2S Bank 1 Sensor 1 Insufficient switching. He performed an air intake system leak test and found no leaks, additionally, they analyzed data from the oxygen sensor, mass airflow sensor, and fuel trims and they were all normal. I also replaced the EVAP canister and the Bank 1 Sensor 1 O2 sensor about a year ago.

The mechanic asked me if I had ever gotten my computer updated and I said no. Apparently there is an update that addresses the engine sending these codes when there is no issue. It only just threw these codes but could they be linked to the dropping oil pressure?

I apologize for the lengthy post but I wanted to give everyone the full story. I have taken the truck to four mechanics and all of them have no clue why the engine would be doing this. It is frustrating because the truck acts perfectly normal but only when I take it on the interstate for a while I get these problems.

 

[swathdiver]

All, I finally tested the truck on another 2 hour trip and have an update. Before I took it on the drive, I ran a camera into the oil pan and saw there was a little bit of sludge in the pan, not a lot, but some. I cleaned it out of the pan and put more oil in.

I took it on the two hour drive and again the oil pressure started strong at 65 psi but slowly dropped to 40psi in about 45-60 minutes. Right on the 40psi mark I got the lifter tick again. The oil continued to drop but held steady around 30psi.

Did you ever make the run with an extra two quarts on board?

 

[Jfarm]

Did you ever make the run with an extra two quarts on board?

I did not, but I was full on oil right before I left. I've heard people say that its fine on the engine but I've heard others say it could create extra strain on the engine. In your experience, do you think that it could cause a problem by driving two hours on it or should I just add it, do a short drive, then drain some of it out? Are there other methods to checking if the O-ring has gone bad? Could the O-ring be failing when it heats up and then be fine when it cools down?

 

[swathdiver]

I did not, but I was full on oil right before I left. I've heard people say that its fine on the engine but I've heard others say it could create extra strain on the engine. In your experience, do you think that it could cause a problem by driving two hours on it or should I just add it, do a short drive, then drain some of it out? Are there other methods to checking if the O-ring has gone bad? Could the O-ring be failing when it heats up and then be fine when it cools down?

On the GM-Trucks forum a guy who was on hard times added two quarts to do the o-ring test and left it that way for a couple of years until he could make the repair. In the old days our crankshafts actually came in contact with the oil in the pan, at least on my Buicks, and it was never an issue. If yours were mine I would add the two quarts and make the run as usual to see if it'll replicate.

 

[Jfarm]

On the GM-Trucks forum a guy who was on hard times added two quarts to do the o-ring test and left it that way for a couple of years until he could make the repair. In the old days our crankshafts actually came in contact with the oil in the pan, at least on my Buicks, and it was never an issue. If yours were mine I would add the two quarts and make the run as usual to see if it'll replicate.

I took your advice and added the two extra quarts. This weekend I had to make the 2 hour drive again. This time was different and may only add to the already puzzling situation.

When I went down Saturday, there was nothing different in what happened. The oil pressure started strong at around 60psi but slowly dropped to 30psi with the lifter tick starting at 40psi. Pressure returned and the lifter tick went away after the truck cooled down later that day.

On the drive back Monday night however, I did not get any ticking. I started the drive at about 55psi and 20 minutes in it dropped to 50. For the rest of the drive, the pressure only slowly dropped to 45psi. Never got a lifter tick.

While the pressure didn't drop all the way, I could tell the oil pressure was not normal. When the pressure acts normal, the pressure will shoot up when I give it some gas. When I am on the highway doing the longer drive, the pressure stays the same even when I give it gas.

Something I will also add, this morning was cold in the low 20's. I started up the truck and only got 30psi. The pressure was jumping up and down 5 psi occasionally. I drove it around after warming it up for a few minutes and randomly the pressure goes back to the normal 45psi with no random 5psi jump in pressure.

What could be causing this? If it were the O-ring, why would the two quart test not work the first time then somewhat work the second time? Could something be in the motor blocking the oil flow and potentially be lodging and dislodging internally over the course of the drive? If so, why only when operated on the highway and not at idle? Should I consider an engine flush? If it were the oil pump, I would believe the issue would appear when the earlier tests were conducted.

Thank you again for all your help on this very odd issue.

 

[swathdiver]

I took your advice and added the two extra quarts. This weekend I had to make the 2 hour drive again. This time was different and may only add to the already puzzling situation.

When I went down Saturday, there was nothing different in what happened. The oil pressure started strong at around 60psi but slowly dropped to 30psi with the lifter tick starting at 40psi. Pressure returned and the lifter tick went away after the truck cooled down later that day.

On the drive back Monday night however, I did not get any ticking. I started the drive at about 55psi and 20 minutes in it dropped to 50. For the rest of the drive, the pressure only slowly dropped to 45psi. Never got a lifter tick.

While the pressure didn't drop all the way, I could tell the oil pressure was not normal. When the pressure acts normal, the pressure will shoot up when I give it some gas. When I am on the highway doing the longer drive, the pressure stays the same even when I give it gas.

Something I will also add, this morning was cold in the low 20's. I started up the truck and only got 30psi. The pressure was jumping up and down 5 psi occasionally. I drove it around after warming it up for a few minutes and randomly the pressure goes back to the normal 45psi with no random 5psi jump in pressure.

What could be causing this? If it were the O-ring, why would the two quart test not work the first time then somewhat work the second time? Could something be in the motor blocking the oil flow and potentially be lodging and dislodging internally over the course of the drive? If so, why only when operated on the highway and not at idle? Should I consider an engine flush? If it were the oil pump, I would believe the issue would appear when the earlier tests were conducted.

Thank you again for all your help on this very odd issue.

Interesting indeed. My memory is not so good, have you replaced just the oil filter to rule this out? We have seen people with oil pressure trouble with Mobil One EP filters and Amsoil filters.

I just reread some of the posts to look for clues. Conventional oil should be ok with that OCI, but if sludge has built up after 21 years I would rather drop the pan then rely on chemicals. Oil filter, PF59 was the original filter, then GM changed it to the PF46. Are those what you are using? Have you ever switched oil types? I have seen where folks switch to synthetic on a 100K mile car and it begins to clean out the system causing all kinds of sludge headaches, especially for the later types, not yours but still same architecture.

 

[Jfarm]

Interesting indeed. My memory is not so good, have you replaced just the oil filter to rule this out? We have seen people with oil pressure trouble with Mobil One EP filters and Amsoil filters.

I just reread some of the posts to look for clues. Conventional oil should be ok with that OCI, but if sludge has built up after 21 years I would rather drop the pan then rely on chemicals. Oil filter, PF59 was the original filter, then GM changed it to the PF46. Are those what you are using? Have you ever switched oil types? I have seen where folks switch to synthetic on a 100K mile car and it begins to clean out the system causing all kinds of sludge headaches, especially for the later types, not yours but still same architecture.

Unfortunately I do not know exactly what filter I have on right now. I have had to go to Jiffy Lube a couple times to change the oil since I did not have any time to do it. I can investigate to try and find what model they have been putting on but I've never used any of those filters that have problems and I believe that they do not use them either.

I am debating about just dropping the pan and looking around to see any issues. If I do drop it, I'm thinking about replacing the whole oil pickup tube and O-ring as well as cleaning anything I see.

I was also reading on another forum that in addition to the O-ring on the pickup tube going bad, the oil pan gasket has two o-rings that seal the inlet and outlet to the oil filter that can go bad. Apparently if one of those two o-rings goes bad, it can push oil back into the pan causing it to lose pressure. Have you heard anything about this? Do you think it's worth dropping the pan at this point?

Thanks again for all your help.

 

[swathdiver]

Unfortunately I do not know exactly what filter I have on right now. I have had to go to Jiffy Lube a couple times to change the oil since I did not have any time to do it. I can investigate to try and find what model they have been putting on but I've never used any of those filters that have problems and I believe that they do not use them either.

I am debating about just dropping the pan and looking around to see any issues. If I do drop it, I'm thinking about replacing the whole oil pickup tube and O-ring as well as cleaning anything I see.

I was also reading on another forum that in addition to the O-ring on the pickup tube going bad, the oil pan gasket has two o-rings that seal the inlet and outlet to the oil filter that can go bad. Apparently if one of those two o-rings goes bad, it can push oil back into the pan causing it to lose pressure. Have you heard anything about this? Do you think it's worth dropping the pan at this point?

Thanks again for all your help.

I've had those o-rings leak near the oil filter before on mine and they caused no pressure issues. I don't know what the latest filters Jiffy Lube is using, used to be Pennzoil and before that Purolator. Anyhow, it might be a good idea to pick up a new PF46 and just swap it out and repeat the drive before dropping the pan and replacing the o-ring.