Another Oil Pressure Quandary

[SweetNubbinz]

Hey folks,

2008 Chevy Tahoe, 5.3L, 177K miles

History of the issue: a few months ago I was coming back from a longer drive (approx 150 miles) and as i exited the freeway my oil dived to near nothing and I received warnings, don't remember the exact wording. I immediately pulled over and shut down and checked the oil. Found it was about a quart low, barely on the stick. I started it back up and things were fine so I started back home. About half way it dropped again but feathering the gas brought it up. I powered through the last half mile that way. I filed the oil when I got home and found the oil pressure lower than usual but steady. I dropped it off at my local mechanic and they wanted to replace the oil pressure sensor. I was doubtful because I had replaced it the year prior when it quit reading altogether. They replaced it and said all was good but my oil was still low. I know my oil was always around 40 at idle and would increase with the throttle as is expected. Following this incident and the repair, it was 20 and would raise a bit with the throttle. The shop says it was within spec. I went home and changed the oil and filter. I have used Royal Purple HMX and WIX filters since I bought the truck with 132K on it. Immediately everything looked good so I figured I just paid $700 for an oil change I did myself. Lesson learned.

So about a month ago, the low oil pressure started again. But I noticed that it was only when cold. After the engine is up to temp, it's back to 40+. This seems opposite of what i would expect. I was under the impression that thicker oil would cause HIGHER pressure then it should lower as it heats up. I changed the oil again at about mid-change interval. No change. What is going on here? Oil pump? Pick up o-ring?

Wish I knew a good mechanic I could trust.

 

[mikez71]

Not sure why the difference... But make sure your oil level is good.

20psi is plenty. Pretty standard for idle I think?

Here is where the low oil pressure warning lamp activates...

 

[donjetman]

Oil pump to its pickup tube o-ring needs replacing every 10 yrs are so.
also
here's a TSB that applies to your vehicle for oil consumption: https://static.nhtsa.gov/odi/tsbs/2014/MC-10114272-9999.pdf

 

[Joseph Garcia]

If you have the old style valve cover, replace it. Also, install an oil catch can, while you are at it.

I believe that you are going to need to drop the oil pan, as I believe that the source of your issue is one or both of the following:

(1) Replace the O-ring on the oil pickup tube, AND purchase a 2-bolt cover plate to better secure the oil pickup tube to the block (hopefully to increase O-ring life).

(2) While you are in there, replace the oil pressure relief valve in the oil pan, AND purchase an oil flow deflector that should be installed with the new oil pressure relief valve.

 

[Marky Dissod]

Here is where the low oil pressure warning lamp activates ...
View attachment 471496

You realize that that table is also tune-able, right?
For example:
RpM: 000 . . . 512 . . . 1024 . . . 1536 . . . 2048 . . . 2560 . . . 3072 . . . 3584 . . . 4096 . . . 4608 . . . 5120 . . . 5632 . . . 6144 & Up
Min Psi tuned: 7.3 . . .. 9.4 . . . . 11.2 . . . 13.1 . . . 15.0 . . . . 17.0 . . . 18.8 . . . . 19.6 . . . 20.7 . . . . 22.6 . . . 24.4 . . . 25.5

See what I did there? Obviously if you raise the numbers too high, you get false warnings from the dummy light,
but it should be clearly evident that people think they need far more oil pressure than they really do.
Do wonder if those numbers differ between engines that Half@$$ vs engines that do not?

 

[mikez71]

Do wonder if those numbers differ between engines that Half@$$ vs engines that do not?

As far as I can tell, pressure warning map is the same between AFM and non-AFM (2009 and 2010 H3 is what I compared with)
2.5 seconds before oil lamp illuminates
15 seconds before low oil pressure message pops up (10seconds for H3)

The 2012 escalade 6.2 are SLIGHTLY higher numbers. (5.3 is this much less than 6.2)

16kpa hysteris
3.50 seconds lamp delay
10 seconds message delay

 

[Marky Dissod]

As far as I can tell, pressure warning map is the same between AFM and non-AFM (2009 and 2010 H3 is what I compared with)
2.5 seconds before oil lamp illuminates
15 seconds before low oil pressure message pops up (10seconds for H3)
View attachment 471520

The 2012 escalade 6.2 are SLIGHTLY higher numbers. (5.3 is this much less than 6.2)
View attachment 471521
16kpa hysteris
3.50 seconds lamp delay
10 seconds message delay

Long story medium: feel free to use the 'best' numbers from ALL the various GM OE Gen3 & Gen4 V8 varieties
(Cadillac Fleetwood V4P LT1 responds nicely to FireBird LT1 shift times, for example.)

 

[mikez71]

15 seconds does seem like awhile to wait before popping the message. little oil light can be hard to notice when driving.. Even 10 is long

 

[Marky Dissod]

15 seconds does seem like awhile to wait before popping the message. little oil light can be hard to notice when driving.. Even 10 is long

The go looking for even better GM OE numbers! Or ...

Friend borrowed my Z71 for a weekend, he was too optimistic about how much gas it said it had left, and had a close call with a gas station.
You best believe that I tuned the fuel gauge display for more pessimism to counterbalance his misplaced optimism

 

[mikez71]

Not too worried about using OE numbers here.. I might do something wild and crazy!!!!

Dangit, negative numbers don't work!

Good idea about the fuel guage.. Like setting clock 5 min early.. but I never do that... against the rule of guaging!

 

[Marky Dissod]

Not too worried about using OE numbers here. I might do something wild and crazy!

When I say 'OE numbers', always remember that I mean the BEST OE numbers available for ANY GM Gen3 / Gen4 V8 vehicle, including cars.
If that's not crazy enough for you, then props yo. I'm merely suggesting being flexible without being TOO crazy.
I prefer having one foot on one side of the line, and then crossing the line with my other foot, y'know?

Dangit, negative numbers don't work!

Not many places where negative numbers work. Where were you thinking?

Good idea about the fuel gauge. Like setting clock 5 min early, but I never do that. against the rule of gauging!

You know how many posts here ask something to the effect of
'is it ok if I ran out of gas like a dumbschidt?' Outgrew that schidt in my late 20s. When I learned my good friend didn't, I accepted that he may never learn.
Instead of dressing him down with that Asking Alexandria song in the background, I tuned around his obstinate ignorance.
Along the same lines of tuning the speedo faster than actual instead of slower than actual ...

 

[mikez71]

I was joking about the negative numbers, but did try to input them just to check what hptuners allowed..

 

[SweetNubbinz]

So, it seems half say it's not a problem and the the other half say it is. When it's been 40 plus and suddenly changes to around 20 (15-25) when cold I should just chalk it up to age? I need to get another 5 years out of this truck with the way prices are today.

I just added a catch can (the Evil one) and in 3 weeks it's almost halfway up the dipstick. I'll be doing the valve cover soon. I recently tore my meniscus so I've got to take things a bit at a time.

 

[j91z28d1]

So, it seems half say it's not a problem and the the other half say it is. When it's been 40 plus and suddenly changes to around 20 (15-25) when cold I should just chalk it up to age? I need to get another 5 years out of this truck with the way prices are today.

I just added a catch can (the Evil one) and in 3 weeks it's almost halfway up the dipstick. I'll be doing the valve cover soon. I recently tore my meniscus so I've got to take things a bit at a time.

so I haven't had it happen to mine, so I can only tell you the trend I've noticed over the last few years of reading pretty much every oil pressure thread I can find.

the oil pressure sensors are junk, like all of them. all fail over time. out of box, a month later, 6 months or 5 years. no one knows when it will fail or how it will fail, some go to zero, some max out. some just flicker around, some leak oil all over the engine. I've had a dead one, a maxed one and a random flicker only after a 30min or longer drive. the best seems to be just stop by a gm parts departments and buy a new one. rock auto is trusted too but no place else. no Amazon or ebay parts ever, and definitely not a off brand from a local auto parts store, except that they are easy to return if they are life time warranty. which leads me to they sell a remote mount for the sensor, I believe they are about 50$ these days, just some fittings and braided line so you can mount it where it's easy to swap when they go bad or need to test if it's bad with a mechanical gauge which is good to have handy.

for the low pressure, if I'm reading your post right, it's backwards to what's common. most usually have high pressure cold and then when up to temp, it thins and drops to 15-20psi at idle 600rpm. if yours is low cold and high hot. I can only guess the sensor is bad again. atleast worth putting a mechanical gauge on it to see if it's real.


from the oil pressure threads I've read the trend seems to be you have 40 psi at idle for anywhere from the first 80k to 180k miles. all of a sudden it drops to 20 or less at idle and everyone goes wtf please tell I don't need a new engine soon. they then look online, get the common it's the o ring that's bad advice cause that's the most logical thing. they pull the pan replace the o ring, might change a few psi. wonder why, turns out there's 3 different size o rings, so they 2nd guess they got the right one. drop pan again. replace with different o ring. still no change, at that point logic says it's the oil pump, front is pulled apart, replacment pump is put on, better but still not the old 40psi. front is pulled apart again, high volume pump is used, oil pressure comes up to around 40 and everyone forgets about it.


the high volume pump just covers for whatever caused it. which is fine, because no one really knows what caused it. theory's range from afm tower o rings leaking, worn cam bearings, worn rod/main bearings, vvt stuff.

usually you take a high mileage junk yard ls apart and the main and rod bearings look good, the cam bearing look worn, but turns out gm align bores the cam bearing after install, and used the cheapest designed bearings know to man. so it's possible copper has been showing from day one.

in the end, it seems anything above the factory minimum spec (which is something crazy like 7psi at a 1000 rpm hot) doesn't shorten the engine life enough to really see a trend is blown up engines. the lifters/cam lobe seems to be the common failure point no matter the oil pressure (the hybrid version run a different oil pump on basically the same ls engine that keeps it always between 50-70psi and engine replacement because of lifter failure is basically running at 100% by 200k miles) that cam lobe to lifter roller interface is splash oiled anyways. my feeling is that's probably failing because of low quality parts used more so than oil, back in the old sbc days or even the older Gen 3 ls engines. the same lifter didn't really fail like these gen 4's. but now days every part is suspect. there's literally no guaranteed good parts anymore to be bought at any price point across basically the entire industry.


my 1.5 cent opinion is double check the oil pressure with a gauge, if it's lower hot than you want. you can try the o ring test of add 2 extra qt of oil, park with the front down hill and see if the oil pressure increases. if it does, the o ring is bad and sucking air. if not just run thicker oil till you get the pressure you want. donjetman on here has run everything from 0w20 to 15w40 or 50 can't remember which right now, with oil sample tests to back it up. no increase in engine wear from any of the weight oil he's run. try a 10w40, if that doesn't do it go 15w40/50. whatever makes you comfortable. I doubt even a 20w50 would cause any problem except maybe a small loss in fuel mileage. I'd guess under a mile per gallon.


good luck with it.

 

[j91z28d1]

As far as I can tell, pressure warning map is the same between AFM and non-AFM (2009 and 2010 H3 is what I compared with)
2.5 seconds before oil lamp illuminates
15 seconds before low oil pressure message pops up (10seconds for H3)
View attachment 471520

The 2012 escalade 6.2 are SLIGHTLY higher numbers. (5.3 is this much less than 6.2)
View attachment 471521
16kpa hysteris
3.50 seconds lamp delay
10 seconds message delay

I believe the delay is for first start up.

I got a buddy with an ls6 right now and for some reason out of the blue it just started losing oil prime or something. if the car sets more than a few hours, it takes a solid 30sec or more to build pressure. once it does come up, it's the same 35 at idle it's always had. the engine sounds perfect no tick or anything at 0psi. my ls3 car sounds worse with oil pressure., it's been apart about 2 years ago, looked over and small. cam put in than last power. so new o ring and all. tried different filters, oils. Confirmed with a mechanical gauge.


Seems way to long, and I can't find a single thread on the net that doesn't just go dead before a reason was found. at this point it's probably going to come out, inspect and put another new pump in it and hope that's it. doesn't make any sense to me thou.

 

[j91z28d1]

The go looking for even better GM OE numbers! Or ...

Friend borrowed my Z71 for a weekend, he was too optimistic about how much gas it said it had left, and had a close call with a gas station.
You best believe that I tuned the fuel gauge display for more pessimism to counterbalance his misplaced optimism

"better" higher oil number would be the hybrid tune numbers. the minimum settings would probably have your oil pressure warnings going off all the time. you'd have to swap in the hybrid pump.

instead of the minimum oil pressure spec being like 7psi, I think it's 35 or something hot idle haha.

I have a feeling the numbers gm put in there for oil is fine for these suv's.

I have thought about lowering the delay on my c6 thou, they have a bit of a known history for kicking rods out of the non dry sump cars in long left handers I believe it is, and at max load high rpm 300deg oil temp, 2 sec without any oil pressure feels like asking for trouble and it's not something you can really look at in the moment, even in the heads up display. there's a lot of other things going on.

 

[mikez71]

This is what hptuners sas about the delay setting..

Right, 15 seconds seems like awhile..
Maybe they figure you'll be watching a big smoke cloud for a few seconds, so they'll let you digest that before throwing the warning message up.. ?

I'll probably change mine to 5 seconds.. 2.5 seconds for lamp, another 2.5 seconds for message to display if pressure hasn't returned....
Unless the low oil pressure warning will do something like throw you in REP mode.. damn computers you never know what'll happen!
I know I don't want REP mode.. almost take runaway throttle over REP mode..

 

[Marky Dissod]

Unless the low oil pressure warning will do something like throw you in REP mode ... damn computers you never know what'll happen!
I know I don't want REP mode ... almost take runaway throttle over REP mode ...

What's REP mode? Never seen it heard of it or experienced it.

 

[mikez71]

Reduced Engine Power.. I'm not saying the oil pressure warning will do that forsure, but if you mess with the throttle maps, and it freaks outs, you get REP.
The throttle barely cracks. 6% or so.. you're almost stuck on the road.. can barely get out of your own way.
I'm sure it's there for safety, but it's a safety hazard itself, imho...

 

[rdezs]

As to his earlier comment about oil pressure increasing once it's warmed up..... While you have the pan off, you might want to take a look at your oil pressure relief valve in the oil pump. Little bits of carbon and whatnot make it stick. Wouldn't be a bad idea just to replace the oil pump itself . (In addition to the aforementioned o-ring, two bolt girdle for the pickup tube, and that pressure relief valve mounted in the oil pan)