5.3 Oil Pressure Advice

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w102acd

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Hey all and sorry for the novel!

I have a 2012 Tahoe LTZ with a 5.3 and 178k miles. We recently had the check engine light come on with P0521 (I think) as the code which is oil pressure sensor. The oil pressure has always been "low" since we've owned it, but recently it would start below 20 psi at cold idle, get down to maybe 15 psi at hot idle, and never got above 25 psi while driving. I've never noticed any ticks or anything as long as I've owned it.

What I've already done:
1. A little over a year ago (February 2022), the oil pressure sensor stopped working completely. The gauge read 0 psi all the time and threw the P0521 code. I put a new AC Delco oil pressure switch and Dorman screen in.
2. This past weekend (March 2023), I was due for an oil change so did a motor flush with the motor medic stuff. I also dropped the pan and replaced the oil pickup tube oring.
3. I'm not going to lie, there have been at least 2 occasions (probably more) where I haven't checked the oil as often as I should have and when I did it either barely registered or didn't register on the dipstick. One of these was last week, but topping off the oil didn't really change anything.

The pressure now, but still not great in my opinion. Cold idle is around 35 psi. Hot idle is around 22 psi. Running (hot or cold) it stays around 35-40, responds to throttle (ie decrease when coasting and increases when accelerating), and never drops below 30 while moving. It hasn't thrown a code in ~100 miles since this past weekend.

I have used Pennzoil High Mileage Synthetic with Fram Xtra Guard Synthetic oil filters as long as I've owned it. Don't kill me, but I change the oil when the truck tells me to (I think it's 7,500 miles).

What do you recommend I do next (in order of cost/ease for me):
1. Do nothing, everything is fine. I've seen some posts on here that have said this behavior is perfectly normal.
2. Change the oil/filter (or just the filter) at 3,000 miles or when the oil pressure gets scary.
3. Change oil and/or filter to something else and/or use a different weight oil and/or oil additive. Not trying to get into a chest pounding session here, but open to ideas if others have direct experience with this fixing this problem. I'm not convinced that the motor flush and/or the oring swap did anything, it may have just been the oil change that increased my pressure.
4. Change the oil pressure sensor and screen again. It's only a year old, but $50 and some scratches/bruises/cussing is easy and cheap.
5. Change the oil pump. Thinking that perhaps between running the engine with low oil and/or a bad oring, I've trashed my oil pump. I am seeing some small surging of the oil pressure all the time. Nothing major, maybe +/-2 psia when RPMs are rock solid (idling or cruising).
6. Sell the truck. I consider this the nuke button since I like the truck, but I don't think I'm willing to dig in deeper than the things above. Not interested in (myself or a shop) removing the DoD/AFM, changing the cam/cam bearings, etc. The juice isn't worth the squeeze for my situation.

For "Change the oil pump" above:
-The old oring was orange and the new oring was also orange so I thought I was good. The old oring had flat spots on the ID and OD, but wasn't split or as brittle as I thought it would be. I was also surprised that the new oring went in as easy as it did. I was expecting/hoping it to need some hard pushing to get it in, but it just kind of slipped in (maybe that's normal). With the oil pump change, I could use the thicker oring (like the green one that comes with the Melling oil pumps). My pickup tube has the tapered end, not the straight end. If I dig into it again, I will use a new Melling pickup tube as well.
-What oil pump should I use? I've read that (at least) the LTZs have a stock high volume pump because they have the towing package and oil cooler. Is that correct? I'm looking at Melling M295 (normal volume/pressure), Melling M295HV (high volume/normal pressure), or Melling 10295/10296 high volume/pressure.
-Should I change the oil pressure relief valve as well while I'm in there? I think it screws into the pan. I'm looking at Melling MOPR100. Are the oil pressure relief valve and the oil filter bypass valve the same thing?

Thanks!
 

tom3

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With the mileage and the oil consumption I'd change the oil more often. Probably getting some blow by and oil contamination that is breaking down the base. I'd go no more than 4k miles. What weight oil are you using? Otherwise I'd live with it.
 

Geotrash

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Hey all and sorry for the novel!

I have a 2012 Tahoe LTZ with a 5.3 and 178k miles. We recently had the check engine light come on with P0521 (I think) as the code which is oil pressure sensor. The oil pressure has always been "low" since we've owned it, but recently it would start below 20 psi at cold idle, get down to maybe 15 psi at hot idle, and never got above 25 psi while driving. I've never noticed any ticks or anything as long as I've owned it.

What I've already done:
1. A little over a year ago (February 2022), the oil pressure sensor stopped working completely. The gauge read 0 psi all the time and threw the P0521 code. I put a new AC Delco oil pressure switch and Dorman screen in.
2. This past weekend (March 2023), I was due for an oil change so did a motor flush with the motor medic stuff. I also dropped the pan and replaced the oil pickup tube oring.
3. I'm not going to lie, there have been at least 2 occasions (probably more) where I haven't checked the oil as often as I should have and when I did it either barely registered or didn't register on the dipstick. One of these was last week, but topping off the oil didn't really change anything.

The pressure now, but still not great in my opinion. Cold idle is around 35 psi. Hot idle is around 22 psi. Running (hot or cold) it stays around 35-40, responds to throttle (ie decrease when coasting and increases when accelerating), and never drops below 30 while moving. It hasn't thrown a code in ~100 miles since this past weekend.

I have used Pennzoil High Mileage Synthetic with Fram Xtra Guard Synthetic oil filters as long as I've owned it. Don't kill me, but I change the oil when the truck tells me to (I think it's 7,500 miles).

What do you recommend I do next (in order of cost/ease for me):
1. Do nothing, everything is fine. I've seen some posts on here that have said this behavior is perfectly normal.
2. Change the oil/filter (or just the filter) at 3,000 miles or when the oil pressure gets scary.
3. Change oil and/or filter to something else and/or use a different weight oil and/or oil additive. Not trying to get into a chest pounding session here, but open to ideas if others have direct experience with this fixing this problem. I'm not convinced that the motor flush and/or the oring swap did anything, it may have just been the oil change that increased my pressure.
4. Change the oil pressure sensor and screen again. It's only a year old, but $50 and some scratches/bruises/cussing is easy and cheap.
5. Change the oil pump. Thinking that perhaps between running the engine with low oil and/or a bad oring, I've trashed my oil pump. I am seeing some small surging of the oil pressure all the time. Nothing major, maybe +/-2 psia when RPMs are rock solid (idling or cruising).
6. Sell the truck. I consider this the nuke button since I like the truck, but I don't think I'm willing to dig in deeper than the things above. Not interested in (myself or a shop) removing the DoD/AFM, changing the cam/cam bearings, etc. The juice isn't worth the squeeze for my situation.

For "Change the oil pump" above:
-The old oring was orange and the new oring was also orange so I thought I was good. The old oring had flat spots on the ID and OD, but wasn't split or as brittle as I thought it would be. I was also surprised that the new oring went in as easy as it did. I was expecting/hoping it to need some hard pushing to get it in, but it just kind of slipped in (maybe that's normal). With the oil pump change, I could use the thicker oring (like the green one that comes with the Melling oil pumps). My pickup tube has the tapered end, not the straight end. If I dig into it again, I will use a new Melling pickup tube as well.
-What oil pump should I use? I've read that (at least) the LTZs have a stock high volume pump because they have the towing package and oil cooler. Is that correct? I'm looking at Melling M295 (normal volume/pressure), Melling M295HV (high volume/normal pressure), or Melling 10295/10296 high volume/pressure.
-Should I change the oil pressure relief valve as well while I'm in there? I think it screws into the pan. I'm looking at Melling MOPR100. Are the oil pressure relief valve and the oil filter bypass valve the same thing?

Thanks!
When I did the first cam swap in my 2012 I changed the o-ring in the pump and used the orange one as you did. I also noticed that it was a relatively easy fit. However, when I started the engine after the swap, my oil pressure was down about 5-10 PSI from where it had been. I tore it down again within 100 miles because a lifter failed due to the lifter trays I used, and this time I replaced the oil pump with a Melling 365HV (high volume), which came with a green o-ring that they said was the correct one for my application (truck). It was a much tighter fit upon installation than the orange one had been previously.

I also changed the relief valve in the pan (it's a pop-off valve so it doesn't really regulate pressure so much as it protects against pressure spikes from the AFM system). When I installed the pump I kept the spring that it came installed in the pump outlet (that's the one that regulates pressure), and when I started it I had great oil pressure again. I tore down the old pump and there was no damage to it and all clearances checked out so I believe that my original pump (factory high-volume) was fine and that my problem was the o-ring I installed the first time around.

Not sure what to suggest, because I know it's a PITA to drop the pan and do the o-ring again. Just relating my experience in the hope it will help you. If you go back in there again, I would replace the relief valve in the pan with new. It can be deleted safely and plugged only if removing the AFM components, which it seems isn't in your plan, which is fine.

For now, you might try a different filter (I run the Wix 57045) and Euro 5w-40 oil. I run the Amazon Basics brand in my 2012 and it's been running like a champ for the last 20K this way. I change my oil every 5K or less.
 
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w102acd

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Hard to believe I left something out of my novel :), but I use 5W-30 Pennzoil High Mileage Synthetic.

Thanks Geotrash for sharing your experience! You don't explicitly say it. Am I correct in assuming the green oring and new HV oil pump fixed your oil pressure problem? Also, why did you use the M365HV rather than the M295HV? Everywhere I've looked says the M295HV is the correct one for me. The M365HV looks to be equivalent. Anyone know the difference?

I'm kicking myself for not replacing the oil pump and oil pressure relief valve while I had it all apart, but happy I didn't pay a shop $1000 to change the $5 oring. If I drop the pan again, I'll definitely do the pickup tube, oring, and pump. On a positive note, it'll be much faster the second time. :)

As of right now, I'll plan to live with it for the next 4,000 or so miles and then drop the pan, change the pickup tube, oring, oil pump, oil relief valve, oil pan gasket, oil cooler gasket, and timing cover gasket. We do have a 1500 mile spring break trip planned so I'll be there pretty quickly. I guess I'll flex as things change (if things get worse or better quicker).

I'll probably replace the oil pressure sensor and screen in the next couple of weeks just to rule that out before I rip into it again.
 

Geotrash

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Hard to believe I left something out of my novel :), but I use 5W-30 Pennzoil High Mileage Synthetic.

Thanks Geotrash for sharing your experience! You don't explicitly say it. Am I correct in assuming the green oring and new HV oil pump fixed your oil pressure problem? Also, why did you use the M365HV rather than the M295HV? Everywhere I've looked says the M295HV is the correct one for me. The M365HV looks to be equivalent. Anyone know the difference?

I'm kicking myself for not replacing the oil pump and oil pressure relief valve while I had it all apart, but happy I didn't pay a shop $1000 to change the $5 oring. If I drop the pan again, I'll definitely do the pickup tube, oring, and pump. On a positive note, it'll be much faster the second time. :)

As of right now, I'll plan to live with it for the next 4,000 or so miles and then drop the pan, change the pickup tube, oring, oil pump, oil relief valve, oil pan gasket, oil cooler gasket, and timing cover gasket. We do have a 1500 mile spring break trip planned so I'll be there pretty quickly. I guess I'll flex as things change (if things get worse or better quicker).

I'll probably replace the oil pressure sensor and screen in the next couple of weeks just to rule that out before I rip into it again.
Happy to help.

The truth is I don't know which of the things I changed actually solved my oil pressure problem because I changed the cam, oil pump, o-ring, and relief valve, all at the same time. Any of which could alone be the cause of low oil pressure. But, what I believe is that the thicker green Melling o-ring is what actually solved my problem.

I chose the M365HV based on a call with Melling's technical team about what I was planning to do. I actually bought it before the first cam swap but didn't install it until the second. I don't remember what the difference was between the 365HV and 295HV.
 
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w102acd

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Gotcha! Since I'm not interested in swapping the cam, I think I'll stick with my plan. However, you bring up an interesting point. I will plan on doing the +2 quart downhill oring test that has been described on this forum to see if my new oring could be all or part of my problem.
 

j91z28d1

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where did you get the oem oil pressure sensor? I got what I thought was oem off Amazon. it looked perfect, bag, numbers and everything. put one in my c6 and then later my 11 Yukon. less than 6 months I notched a flicker in the gauge on a hour drive, like huh. it finally got worse to where I was sure it wasn't the engine but the sender. I went back to the Amazon listing and sorted like 500 reviews by 1 to 2 stars. lots of people saying it seems to be a counterfeit ACDELCO. now I have no idea how this could be, but I went ahead and stopped by the dealer, had them match gm parts direct pricing and got a new one. matched them up and everything looks the same, but the font on the sensor body is different from the original I still had and the new dealer one.

my car still has the iffy sensor. it's a manual, so no rpm flare in gear, but say you're rolling down the road steady at 2500rpm, you step in the gas some and oil pressure drops a few psi before building with raising rpm. we kinda all figured it was rod bearing wear since I've abused this poor engine badly. many track days, belt slung over heated horribly, then drive it a 1000miles home on the baked oil. reduced power mode and all. but after a oil hose burst last trip, I had the bottom end apart to inspect bearings and they all look fine. I believe the Amazon ACDELCO sensor is doing weird stuff.
middle pic is the Amazon one.

so for me, I'd throw a dealership or gm parts direct sensor in it, switch to mobile 1 10w40 (just my preference, no clue if it's any better brand) but definitely at least some 10w40 and drive it till I notice any issues.


this is also a good pod cast from millings about ls oil pumps and issues.

 

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w102acd

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Gotta love this forum! As a matter of fact, I did buy the "ACDELCO" oil pressure sensor from Amazon because it was like $30. I remember thinking at the time, "how can Amazon sell them for half the price of an auto parts store?" However,then moved on to "it's an ACDELCO part, so what do I care?" Sounds like a screen and oil pressure sensor change (to a real GM part) would be a good things to do this weekend. Thanks for sharing your experience!

Looking at this one (I assume GM genuine on Rock Auto is legit?):

Does anyone know the "criteria" for the check engine light and P0521 code? I've read somewhere that its very low, like 6 psi or something like that. It has me thinking perhaps my sensor is going bad because I haven't noticed anything this low since I put the (maybe/maybe not ACDELCO) oil pressure sensor in a year ago.
 
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w102acd

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For reference, here is the oil pressure switch I ordered from Amazon:

The store is even called "GM Store", but I see the same reviews as j91z28d1 did when looking at the 1 star ratings. Lots of complaints of oil leaking through the housing and into the connector. One of them even references RockAuto ("RA") as being a good part.
 

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