Oil pressure drop 2007 Tahoe 5.3

[kingbeepa]

Over the past month, ‘07 Tahoe has had a low pressure alarm that indicates “Oil pressure low stop engine.” 240k miles. Oil level is full.

In response, I have correctly installed:
Oil pressure sensor, oil level sensor terminal connector, oil pick up tube assembly with new O-ring, oil reservoir gasket, and changed oil plus oil filter.

At least two things I have not addressed:
Oil level sensor, oil pump

As I’ve thrown a bunch of $$ at this mystery, which one of the two or some other thing should I begin with to get the warning alarm to stop?
What error codes would a computer likely tell me?

 

[wjburken]

Did you clean the screen below the oil pressure sensor?

Did you confirm oil pressure with an analog gauge?

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

First step is to purchase a mechanical oil pressure gauge, and they are available at Harbor Freight. Other folks here will chime in on exactly where to connect it.

This will tell you if your current pressure gauge is reading correctly or not, which is often the case in these situations. You can view the oil pressure with the accessory on with the motor off, the pressure at cold idle, the pressure at hot idle, and the pressure while driving (if you temporarily attach the gauge face to the windshield).

From there, there should be a straighter path to determining the source of your issue.

 

[kingbeepa]

Did you clean the screen below the oil pressure sensor?

Did you confirm oil pressure with an analog gauge?

Good things to consider!

There was no screen under the pressure sensor in the expected spot. Research turned up a common practice to remove the screen since they tend to clog. I was not surprised to see it missing and I did not install the one that came with the new one to stay consistent.

I have no analog gauge, but it sounds pretty straightforward based on research I’ve read.

To play devil’s advocate, what if these two leads turn up more failures? Go buy a computer reader? Change to a thicker oil?

 

[Marky Dissod]

If you use the engine during the winter, thicker oil is a liability.

Before addressing the oil pump, do a used oil analysis.
If it turns up too many wear metals, even a 'V4 mode' oil pump will only delay the inevitable at best;
better to start shopping for a 6.0L.
If the wear metals are low enough, then maybe try an oil pump used in V4 mode engines?

 

[wjburken]

Good things to consider!

There was no screen under the pressure sensor in the expected spot. Research turned up a common practice to remove the screen since they tend to clog. I was not surprised to see it missing and I did not install the one that came with the new one to stay consistent.

I have no analog gauge, but it sounds pretty straightforward based on research I’ve read.

To play devil’s advocate, what if these two leads turn up more failures? Go buy a computer reader? Change to a thicker oil?

Before you can move forward, you need to understand if you have a pressure generation issue or a pressure sensing issue. If it’s a pressure generation issue, you’ve already taken care of the most common issue which is the o-ring on the pick-up tube.

You already have a “V4” oil pump since your Tahoe has AFM. You may have a by-pass relief stuck open on the oil pump that is keeping it from producing pressure.

Find out if you truly have a pressure issue with an analog gauge and go from there.

 

[donjetman]

@kingbeepa
VLOM orings at towers may be leaking.

 

[strutaeng]

If not the VLOM, then most likely cam bearings or rod/main bearings.

My LQ4 had 260k miles when I tore it down due to a lifter tick. When it was cold (less than 40F) I would get the "low oil pressure" on the instrument cluster momentarily, then pressure would be okay. My cam bearings were kinda worn, but seemed typical. The rod/main bearings had minimal wear. I went ahead and replaced the cam/main/rods bearings since engine was torn down.

The oil pressure increased a little, but I haven't gotten the low oil pressure on start-up...well, it hasn't actually dropped to below 40F here yet. But oil pressure is usually "60" on the garage on cold start-up so I'm not expecting low oil pressure. I'm at 266k now, as a daily driver.

 

[j91z28d1]

confirm lack of oil pressure is real. if so, replace with high volume aftermarket pump. drive till blows up or you get sick or it. whichever comes first haha.


bit confused thou, is the low oil code being set all the time, or only sometimes? have you been driving it around with it saying pull over for lack of pressure.



yours sounds lower than most. but I've seen more than a few threads about low oil pressure. drop the pan to change o ring, new pressure sensors and stuff only to laster go back in for a high volume pump. no clue why it's still low, but the pump hides it and they don't seem to blow up soon after. so eh.

 

[petethepug]

I had my Indi replace the oil pressure gauge when the trans was being replaced. Pretty sure he didn’t use OEM because it reads 30-60-120-90lb sporadically and then freaks and goes to zero which sets off the alarm.

The manual gauge will verify a brand new, bad, outta the box sensor and/or harness issue.

 

[kingbeepa]

confirm lack of oil pressure is real. if so, replace with high volume aftermarket pump. drive till blows up or you get sick or it. whichever comes first haha.


bit confused thou, is the low oil code being set all the time, or only sometimes? have you been driving it around with it saying pull over for lack of pressure.



yours sounds lower than most. but I've seen more than a few threads about low oil pressure. drop the pan to change o ring, new pressure sensors and stuff only to laster go back in for a high volume pump. no clue why it's still low, but the pump hides it and they don't seem to blow up soon after. so eh.

It begins pressure reading around 20 then slowly drops til it alarms.

Yes, I do drive it for a short period before stopping, then it resets the cycle after starting up the engine again.

Already replaced O-ring, pickup tube, oil pan gasket (fixed the leak), oil pressure sensor, and the connector plug for the level sensor… so far.

Also, this all happened after changing the oil and filter. What brand is best to rule out lack of quality in the big picture?

 

[Charlie207]

It begins pressure reading around 20 then slowly drops til it alarms.

Yes, I do drive it for a short period before stopping, then it resets the cycle after starting up the engine again.

Already replaced O-ring, pickup tube, oil pan gasket (fixed the leak), oil pressure sensor, and the connector plug for the level sensor… so far.

Also, this all happened after changing the oil and filter. What brand is best to rule out lack of quality in the big picture?

I think any 5W-30 Dexos 1 and up oil would be fine. As far as filters go, probably any new name brand filter would be fine to test the pressure issue.

I'd still look at the VLOM gasket as another place it could leak. RockAuto: https://www.rockauto.com/en/moreinfo.php?pk=11378161&cc=3305712&pt=10710&jsn=11275

 

[Marky Dissod]

As far as filters go, probably any new name brand filter would be fine to test the pressure issue.

My admittedly blunt rule of thumb for oil filters is as follows:
Never buy any brand name's 'basic' offering.
I.E.:
instead of Fram's PH3675, try XG3675 or TG3675
instead of Purolator L25288, try PBL25288
instead of Wix 51522, try 51522XP
Mobil1 M1-206 doesn't have an upgrade, right?

Also, I prefer ACDelco PF61 over the parts mungqi's 'recommendation'.

 

[j91z28d1]

It begins pressure reading around 20 then slowly drops til it alarms.

Yes, I do drive it for a short period before stopping, then it resets the cycle after starting up the engine again.

Already replaced O-ring, pickup tube, oil pan gasket (fixed the leak), oil pressure sensor, and the connector plug for the level sensor… so far.

Also, this all happened after changing the oil and filter. What brand is best to rule out lack of quality in the big picture?

I wish I could find it, someone posted a video on here of a cam bearing, pan off looking up you could see the bearing had moved and was showing enough to uncover the oil passageway. that would be a major internal pressure leak.


so my 2 cents on oil pressure, atleast what makes sense to me. if you have zero pressure with a high volume pump after it's warmed up, that's a major leak, blockage or sensor failing in a less common way. for leaks there's a bypass valve in the pump that can get stuck and just dump all the oil back into the pan before pressurizing the engine. on some years there's what'd called a afm bypass valve on the inside drivers side of the pan. it's set at 60psi bypass, if it stuck open it could bypass a ton of oil.. as for the vlom gaskets, some preach they can leak, if you still have the afm lifters in place, it doesn't matter. they are vented when the vlom solenoids are not sending oil pressure down to the lifters. my disable kit I installed it has you literally cut the gaskets off those ports and leave them open to vent any backed up pressure that could unintentionally activate the afm lifter. I saw no drop in oil pressure cutting the gaskets off and leaving the holes open. if you have switched to non afm lifters, those ports should be blocked. but I find it hard to believe you'll drop to zero psi over all 8 being left open.



as for o'ring, instead of pulling everything apart to try new sizes, just find a steep ish hill and park nose down, the oil will cover the o'ring. if the oil pressure comes up, the o'ring is leaking, if not. eh. you can also add 2 extra qt of oil at idle. that will cover the o ring too. Just don't drive around much with 2 extra in there. I think there's 2 posts out of 509 where replaceing an o'ring fixed it completely.


mechanical oil pressure gauge is where to start, there's a oil port on a ls on the front drivers side of the block, it's in the oil galley right after the oil pump, before the filter, so that would rule out cheap filter lowering oil pressure.


if you do end up with the pan off again, look up in there and make sure all the cam bearings are where they should be.


at that point if you don't want to pull the engine to find the issue. might be interesting to throw one of the hybrid pumps on it for a science experiment. they fit a standard ls engine but are a vain style variable displacement pump more like what the newer LT engines have now, and will flow a very high volume of oil. total Band-aid but just for reference, the normal engine gm minimum spec for oil. pressure hot is something like 7psi at 1000 rpm. the hybrid minimum is 36psi hot at 1000 rpm. mine sets at 50-60psi at all times.

 

[Charlie207]

I wish I could find it, someone posted a video on here of a cam bearing, pan off looking up you could see the bearing had moved and was showing enough to uncover the oil passageway. that would be a major internal pressure leak.


so my 2 cents on oil pressure, atleast what makes sense to me. if you have zero pressure with a high volume pump after it's warmed up, that's a major leak, blockage or sensor failing in a less common way. for leaks there's a bypass valve in the pump that can get stuck and just dump all the oil back into the pan before pressurizing the engine. on some years there's what'd called a afm bypass valve on the inside drivers side of the pan. it's set at 60psi bypass, if it stuck open it could bypass a ton of oil.. as for the vlom gaskets, some preach they can leak, if you still have the afm lifters in place, it doesn't matter. they are vented when the vlom solenoids are not sending oil pressure down to the lifters. my disable kit I installed it has you literally cut the gaskets off those ports and leave them open to vent any backed up pressure that could unintentionally activate the afm lifter. I saw no drop in oil pressure cutting the gaskets off and leaving the holes open. if you have switched to non afm lifters, those ports should be blocked. but I find it hard to believe you'll drop to zero psi over all 8 being left open.



as for o'ring, instead of pulling everything apart to try new sizes, just find a steep ish hill and park nose down, the oil will cover the o'ring. if the oil pressure comes up, the o'ring is leaking, if not. eh. you can also add 2 extra qt of oil at idle. that will cover the o ring too. Just don't drive around much with 2 extra in there. I think there's 2 posts out of 509 where replaceing an o'ring fixed it completely.


mechanical oil pressure gauge is where to start, there's a oil port on a ls on the front drivers side of the block, it's in the oil galley right after the oil pump, before the filter, so that would rule out cheap filter lowering oil pressure.


if you do end up with the pan off again, look up in there and make sure all the cam bearings are where they should be.


at that point if you don't want to pull the engine to find the issue. might be interesting to throw one of the hybrid pumps on it for a science experiment. they fit a standard ls engine but are a vain style variable displacement pump more like what the newer LT engines have now, and will flow a very high volume of oil. total Band-aid but just for reference, the normal engine gm minimum spec for oil. pressure hot is something like 7psi at 1000 rpm. the hybrid minimum is 36psi hot at 1000 rpm. mine sets at 50-60psi at all times.

Yeah, the machinist that looked over my project engine said that the only bearings he's seen actually wear out in an LS are the cam bearings; the mains and con-rods all seemed to last forever as long as no serious trash passed through the oil system. (like mine, luckily)

The other thing to consider is that a high-volume pump can lead to high pressure over time, if the the oil passages start to build up with gunk, causing the relief valve to wear out.

From another forum about Melling oil pumps:

• M295: standard volume/ standard pressure
• 10295: standard volume/ high pressure
• 10296: high volume/ standard pressure

The 10296 flows 30% more oil compared to the M295, and was designed for DoD engines that needed the higher volume of oil to operate the AFM lifters. It was never meant for non-DoD engines. Allegedly you can provide too much volume that it starts increasing case pressure through the galleys and back in to the pump, causing the relief valve to constantly be open. (remember, pressure is resistance to flow.)