03 Silverado oil pressure

[Thunderbolt]

My Chevy 2500HD 6.0 liter has developed a problem. My oil pressure has always been 40 psi at idle and 50-55 psi on the freeway.
Yesterday it started idling at 30-35 psi and 50-55 psi on the freeway.I know it is within specs, but why did it change overnight ? The other thing I noticed is that the gauge responds slower than it used to and on the freeway it can be erratic at times. It will jump back and forth between 50 and 55 psi and sometimes it does the same thing between 30 and 35 psi at idle. The instrument cluster has the updated stepper motors as well, but I am wondering if the sending unit could cause this or if it is something mechanical. Why would it happen overnight ? I also changed the oil and filter with a new AC Delco filter and Mobil One 5w30 oil. Any input would be appreciated.

[BurbMan]

I had a similar mystery pressure drop on my 8.1L...the pressure would still fluctuate across the RPM range was about half of what it used to read...at one point the pressure was down to around 15 psi at idle, but not low enough to show a low pressure message.

Issue turned out to be the oil filter. I had my shop do an oil change when it was in for some other work, and when it was time for an oil change again, I saw the filter had a huge dent in one side!! A new filter brought the oil pressure back to where it had always been.

Likely not your issue since you just did an oil change but thought I would share.

[Thunderbolt]

LIKE2BUILD wrote:

Thunderbolt wrote:
Stepper motors have were replaced last year. No issues with the truck at all and it does have 206,000 miles. I read about the O-ring, but it seems I have different symptoms. I may spend the 60.00 and replace the sending unit and see what happens.

Even repaired stepper motors can go bad. But, I agree, I'd put an ODBII reader on it and see what values are being reported.

One priceless thing I've found is an ELM327 ODBII Code Reader and then I installed the DashCommand App on my phone. This is really handy because any time there is a CEL you can check and clear codes but you can also look at PID's like oil pressure in live time and see what's really happening.

If the pressure is out of whack and the gauge is in-line with what the app says, then you could look at the sending unit. If a new sending unit doesn't change anything then you might look at the oil pump o-ring issue.

KJ

I am going to buy one of those and download the app.

[Thunderbolt]

BenK wrote:
Agree with Kevin and add

Did you just 'cleanse' the oil system with some sort of chem? It might have loosened something to partially clog the intake of the oil pump

Agree with others...did this happen after your oil change and filter change? Some filters, even the best, can has a marginal one to limit oil flow. If it has a high flow restriction, it will become a limiting component for oil pressure

Also agree with Kevin and your mechanic should likewise use a 'good' pressure gauge tapped into the line to check it.

Otherwise shooting in the dark changing out parts to just by chance nail the problem

I did not cleanse the engine and they oil change was after the pressure issue and no change. I have always ran Mobil One as well. I spoke with a mechanic and he said usually if there is an issue with the o-ring or cam bearing the oil pressure is in the single digits so he didn't think it was an issue. He said it could be the sending unit or possibly the relief valve in the oil pump isn't completely closed. I am ordering a oil pressure tester and checking it manually. The lowest the pressure goes at idle is 30-35 and still runs at 50-55 on the freeway. With it happening suddening and the erratic gauge I am hoping it turns out to be the sending unit. I am also thinking about putting some ATF in the crankcase and running it a little while and changing the oil again.

[BenK]

Agree with Kevin and add

Did you just 'cleanse' the oil system with some sort of chem? It might have loosened something to partially clog the intake of the oil pump

Agree with others...did this happen after your oil change and filter change? Some filters, even the best, can has a marginal one to limit oil flow. If it has a high flow restriction, it will become a limiting component for oil pressure

Also agree with Kevin and your mechanic should likewise use a 'good' pressure gauge tapped into the line to check it.

Otherwise shooting in the dark changing out parts to just by chance nail the problem

[LIKE2BUILD]

rhagfo wrote:

I all my years of vehicle ownership, I have never had the dash gauge fail, it has always been the sending unit.

Dash clusters in that era of GM vehicles were notorious for stepper motors going bad.

KJ

[rhagfo]

Thunderbolt wrote:
Stepper motors have were replaced last year. No issues with the truck at all and it does have 206,000 miles. I read about the O-ring, but it seems I have different symptoms. I may spend the 60.00 and replace the sending unit and see what happens. I just find it odd that it happened overnight and the O-ring thing scares me a little. I have the ability to fix it, but I really hope I don't have to do it because my wife hates it when every other word out of my mouth is a swear word.

I all my years of vehicle ownership, I have never had the dash gauge fail, it has always been the sending unit.

[dodge_guy]

I’ve seen sending units go bad on those. I’ve also seen the little screen underneath the sensor get plugged up from sludge. Are you changing the oil frequently or are you going by the oil life monitor which could potentially let oil changes go to 10k miles?
Either way you need to have the oil pressure physically checked with an actual gauge screwed into the oil pressure port.

[bucky]

The 4.8, 5.3, and 6.0 gassers of that vintage are known for blocked oil passages to the lifters at high mileages. Are you hearing any valve train noise at idle that goes away at higher RPMS? Seafoam and Marvel Mystery oil can help if so. Lots of vids on Youtube about it.

[FlatBroke]

My 03 dmax showed “low”pressure since it was new, put in a new sending unit a couple of years ago and pressure shows considerably higher now.

[LIKE2BUILD]

Thunderbolt wrote:
Stepper motors have were replaced last year. No issues with the truck at all and it does have 206,000 miles. I read about the O-ring, but it seems I have different symptoms. I may spend the 60.00 and replace the sending unit and see what happens.

Even repaired stepper motors can go bad. But, I agree, I'd put an ODBII reader on it and see what values are being reported.

One priceless thing I've found is an ELM327 ODBII Code Reader and then I installed the DashCommand App on my phone. This is really handy because any time there is a CEL you can check and clear codes but you can also look at PID's like oil pressure in live time and see what's really happening.

If the pressure is out of whack and the gauge is in-line with what the app says, then you could look at the sending unit. If a new sending unit doesn't change anything then you might look at the oil pump o-ring issue.

KJ

[NMDriver]

I do not claim to be an expert but what was the oil before you changed it? I have been told that a switch from fossil oil to synthetic will cause a oil pressure change. I cannot say if it is true or not since I have always used synthetic oil with the API CJ-4 and CI-4 Plus rating.

[enblethen]

I would be looking at the sending unit. Many GM products use the sending unit as a switch for the fuel pump. Look for leak on sending unit.

[Thunderbolt]

Stepper motors have were replaced last year. No issues with the truck at all and it does have 206,000 miles. I read about the O-ring, but it seems I have different symptoms. I may spend the 60.00 and replace the sending unit and see what happens. I just find it odd that it happened overnight and the O-ring thing scares me a little. I have the ability to fix it, but I really hope I don't have to do it because my wife hates it when every other word out of my mouth is a swear word.

[TakingThe5th]

Have you tried testing oil pressure from the ODB2 connector? That might tell you if the sensor is bad.

I’m also told that when the gauge starts acting up, turn off the engine and restart immediately-if the gauge reads normally you have a stepper problem.

Hope that helps.