Drop in oil pressure

[clandr1]

Hey guys, up until about a year ago my truck would hold a minimum of 40 psi oil pressure at idle no matter whether the motor was cold, or warm. After a 6 hour each way trip in March of 2021, I noticed my "hot" oil pressure was around 30 psi. As this summer has set in, I've noticed the hot idle oil pressure dropping to around 25 psi as of late after 2+ hour road trips, but when I'm driving, pressure is still at or above 40, depending on throttle position and load.

Background: I have used Mobil 1 High Mileage 5w30 full synthetic religiously since 75k miles, always change the oil when the computer tells me, and I've always used quality oil filters. I have also sent my oil off to Blackstone half a dozen times or so, and nothing has been concerning. The most recent analysis was May 2021 at 226k miles (approx. 14k miles ago) and all looked good, nothing outside of tolerance when compared to my historical oil reports dating back to 133k miles.

I should mention that I replaced the pickup tube O-ring in late 2017 around 170k miles after the motor developed a slight ticking noise (the O-ring was replaced immediately, and I do not believe I sustained any damage from the low oil pressure).

I figure the most likely options for me are as follows:
1. Keep driving it and not worry about it until it goes below an arbitrary level (20 psi?)
2. Use thicker oil (if you think this is the right choice, please tell me what weight you think would be best - I'm leaning towards 10w40 if I make a change here)
3. Proactively repair/replace motor internals (please be specific, and keep in mind this is not something I would tackle personally and would likely have to pay a shop to do the work which terrifies me)


I would appreciate any constructive feedback or opinions. Thank you.

 

[Matahoe]

I only see 30 psi at idle when stopped at an intersection for instance. This would be hot ambient temps as well. Roughly 40 -60 psi any other time driving. Is your oil pressure needle moving relative to throttle input/load?

 

[Matahoe]

You may be suffering from a slight filter screen blockage. You can remove the oil pressure switch and take it out spray some carb cleaner on it in reverse flow direction. May want to replace pressure switch which is cheap insurance at your mileage.

If your up to it I would then try an oil flush. Throw in a couple quarts of kerosene or K&W Gunk engine flush. It has similar ingredients but more pricey.

 

[MassHoe04]

There is also some chance that your pressure is not actually a problem...

Do you know for sure, that the pressure sending unit functioning properly and that the pressure gauge in the cluster is indicating the correct pressure based on voltage received from the sending unit?

See if you can get an oil pressure test gauge on there and check cold and hot pressures with the external test gauge.
I'd hate to see you tearing things apart, if it turns out there is something stupid in the electronic reading and display of information.

 

[Joseph Garcia]

20-25 psi at hot oil idle is normal. As long as it goes back up to 40+ psi over 2000 rpms.

 

[Skeeter]

I suspect the oil pressure sensor. I bought my used Yukon Denali at 110K and the oil pressure never dropped below 40 psi and cruising at 75 mph 60 psi. Last month the pressure suddenly read 0. Changed the oil pressure sensor and the pressure is back. Now the pressure at idle is 20 psi and cruising 45 psi. I suspect the old sensor was reading high. Change it yourself if you can. I took it to a shop and they charged me $650 as normal procedure is to remove the intake to get to the sensor. There are YouTube videos on how to do it without removing the intake.

 

[Fless]

You may be suffering from a slight filter screen blockage. You can remove the oil pressure switch and take it out spray some carb cleaner on it in reverse flow direction. May want to replace pressure switch which is cheap insurance at your mileage.

If your up to it I would then try an oil flush. Throw in a couple quarts of kerosene or K&W Gunk engine flush. It has similar ingredients but more pricey.

There should not be a filter screen on a non-AFM engine.

 

[Cbncanada]

It could be one or more of several issues. First go to a 10W30 oil and new filter. Have the engine oil system flushed. Run a can of Sea Foam liquid mixed into the oil to do additional cleaning. That would help if you have sludge deposits reducing the oil flow. Other issues could be the front cam bearing is getting worn. This one will affect oil pressure.

 

[Matahoe]

Sea foam really isn't meant to be added to your oil. Just intake and fuel system. SF is primarily a fuel system drier comprised of mostly isopropyl alcohol..nothing else.

 

[MassHoe04]

On my 4.0L 2005 Jeep Rubicon, I kept up with oil changes every 3k miles. It got cleaner with every oil change.

I was hesitant to do any kind of deep clean with solvents or things like Seafoam or the old ATF fluid in the oil trick.
My gut was telling me it might do more harm than good on an old high mileage engine.

I figured it took years for deposits to build up on seals and gaskets. It wasn't leaking a drop on the ground. If I did a hard cleanse, I was afraid the deposits that were helping keep the oil in would not be there anymore and the oil would start spewing out like a faucet. Oil pan gasket and RMS never spilled a drop! I left it that way and just did the frequent oil changes.

Here is what it looked like inside when I did the valve cover gasket replacement... It had 183k when I bought it and it was about 225k here after 3 years.

 

[clandr1]

Is your oil pressure needle moving relative to throttle input/load?

Yes, it is. While driving, it is at or above 40 psi.

Do you know for sure, that the pressure sending unit functioning properly and that the pressure gauge in the cluster is indicating the correct pressure based on voltage received from the sending unit?

Yes, in May 2021 my oil pressure gauge spiked to 80 psi permanently. I tracked this down to the oil pressure sensor, and after replacement, it has been operating as expected since. I have no reason to believe the gauge is reporting inaccurate information.

20-25 psi at hot oil idle is normal. As long as it goes back up to 40+ psi over 2000 rpms.

Thanks, it may just be normal wear on a high mileage engine that is still above operating spec, just not as good/high as it used to be.

 

[Cbncanada]

Sea foam really isn't meant to be added to your oil. Just intake and fuel system. SF is primarily a fuel system drier comprised of mostly isopropyl alcohol..nothing else.

On the contrary. It is meant to go into your oil as well. It will clean your system and refresh seals etc. Read the label on the can.

 

[Matahoe]

On the contrary. It is meant to go into your oil as well. It will clean your system and refresh seals etc. Read the label on the can.

It's my opinion it won't work. Go ahead and put it in. It's your car. You do realize it's just isopropyl alcohol... No detergents or solvents. Pretty mild. SF was never meant to be used when flushing an engine. That prescription just ain't on the bottle.

 

[S33k3r]

I'm just going to place this right here: HOW TO ADD SEA FOAM MOTOR TREATMENT TO CRANKCASE OIL

 

[clandr1]

Updated the OP for a little more detail that PSI seems to be normal when the truck is moving, my main concern is with PSI at idle when the motor is hot.

I forgot to mention I used Liqui Moly motor oil flush in June 2021 without any change, so I'm not sure an engine flush is going to fix the low pressure.

 

[Mudsport96]

My Silverado runs 40 to 50ish at highway speeds and 20ish at idle, if i wind it out around 5500 to pass it will clear 60 psi. You are probably fine.

 

[Matahoe]

Make sure your using an ACDelco PF-61e or PF-46e filter. There are a few service bulletins regarding it. If that don't fix the issue then at least it's been ruled out...

 

[Matahoe]

Updated the OP for a little more detail that PSI seems to be normal when the truck is moving, my main concern is with PSI at idle when the motor is hot.

I forgot to mention I used Liqui Moly motor oil flush in June 2021 without any change, so I'm not sure an engine flush is going to fix the low pressure.

Seems like you've covered a bit already. My only remaining concern would be to check that the correct ACDelco PF-46 oil filter is being used. And also it seems per the owners manual that 5W-30 synthetic is the recommended grade of oil that covers a wide range of owners situations. Try that as well. If you got to this point you will want to get a oil pressure gauge for manual testing purposes.

 

[clandr1]

Seems like you've covered a bit already. My only remaining concern would be to check that the correct ACDelco PF-46 oil filter is being used. And also it seems per the owners manual that 5W-30 synthetic is the recommended grade of oil that covers a wide range of owners situations. Try that as well. If you got to this point you will want to get a oil pressure gauge for manual testing purposes.

Great point - I have used nothing but AC Delco PF46E filters for at least the last few years. Prior to that I used Wix, Mobil 1, or NAPA Gold so I've always used what I consider to be "good" oil filters, based on what I've read online.

Can you clarify your mention of the owner's manual calling for 5W-30? Maybe I wasn't detailed enough but I have used Mobil 1 High Mileage 5w-30 synthetic since 2011 or so - perhaps you were under the impression I wasn't using that type/weight oil.

 

[clandr1]

Based on the feedback in this thread, I think I'm just going to keep driving it as is with no changes. I've read online that minimum oil pressure spec per GM is 10 PSI per 1k RPM, and if that's truly the case maybe I shouldn't worry about it until it drops below that threshold.