Oil pressure issue

[builds4christ]

Hey all,

Sorry if I'm beating a dead horse here. Just looking for some wisdom.

Got an 08 L92 Yukon. Picked her up pretty cheap! She's got 193k and seems to run well.

Had low oil pressure when I got her. I dug in, melling pump with the spring that came in it, new pickup tube and oring, removed the relief valve in the oil pan, new oil pressure sending unit, new dipstick tube oring, threw in some 10w40 and when it's cold it gets great pressure!

Cold it idles (in park) at about 60-70psi. After a drive and full warm up, it idles at roughly 25 psi.

After warm up, it cruises at 37 or so psi. Cold, close to 80 at cruise.

Just not sure why there's such a large swing. Otherwise, the pressure responds as it should. Rev and it climbs. It's not erratic or erroneous from what I can tell.

Is she just worn out? Am I safe at these pressures?

Thanks so much for any advice. I'm used to the older iron SBC. I never have pressure issues with my older engines and I'm trying to learn the LS platform quirks.

 

[SpareParts]

Normal. Combination of cold vs hot oil, bearing ware and aluminum engines expand slightly more than iron blocks.
As long as you have 25psi hot you have nothing to worry about.

 

[builds4christ]

Ok thank you, I appreciate that. Would you recommend me running any heavier weight oil for the wear or maybe a quart of Lucas? How about running the engine a tad cooler? It's got a 174 stat in it, but the fans kick on at stock temp. Was going to lower the fan kick on temps a bit. Was thinking that might be good since it's procharged.

Yeah aluminum is light weight, but for me has been something to get used to. Especially when torquing things down lol.

 

[thefrey]

I would say that's pretty normal. Nothing big to worry about imo.

I used to get 15psi hot idle, 28-32 cruising, and 45 cold start. After a new melling HV pump and DOD delete I get 60-70 psi cold start and higher when cold cruise, 25psi hot, and 42-45 cruising. I have 225k and some change right now. I am running 5w30.

I like the profile pic FYI. Would love to hear more about it.

 

[Joseph Garcia]

Hey all,

Sorry if I'm beating a dead horse here. Just looking for some wisdom.

Got an 08 L92 Yukon. Picked her up pretty cheap! She's got 193k and seems to run well.

Had low oil pressure when I got her. I dug in, melling pump with the spring that came in it, new pickup tube and oring, removed the relief valve in the oil pan, new oil pressure sending unit, new dipstick tube oring, threw in some 10w40 and when it's cold it gets great pressure!

Cold it idles (in park) at about 60-70psi. After a drive and full warm up, it idles at roughly 25 psi.

After warm up, it cruises at 37 or so psi. Cold, close to 80 at cruise.

Just not sure why there's such a large swing. Otherwise, the pressure responds as it should. Rev and it climbs. It's not erratic or erroneous from what I can tell.

Is she just worn out? Am I safe at these pressures?

Thanks so much for any advice. I'm used to the older iron SBC. I never have pressure issues with my older engines and I'm trying to learn the LS platform quirks.

What you're experiencing is completely normal for your setup. Removing the oil pressure overflow valve in the oil pan removes the topline oil pressure limiter. Close to 80 psi cold and 25 psi idle hot are exactly where they should be. Oil viscosity changes with temperature.

I would warn you not to let the oil pressure exceed 80 psi, as you don't want to damage any oil seals. I am in the same boat as you, and when it is below 50 degrees here, I always remote start the truck and let it idle for at least 10 minutes, before moving it. And, when I do move it, I watch the oil pressure gauge very closely, and I baby the truck/motor rpm's so as not to exceed 80 psi. Once the oil warms up, and gets below 70 psi, then I'm ok to go without limitations.

I am curious, though, why are you running 10W-40 motor oil, when the published motor oil spec is 5W-30?

 

[Marky Dissod]

Would you recommend me running any heavier weight oil for the wear, or maybe a quart of Lucas?

5W30 is fine. I get why people go to 10W40 when the spec is 5W30, ok, whatever.
Solid NO to Lucas. Choose the right motor oil (Valvoline Restore & Protect 5W30, just an opinion), change it early / often enough, never need additives,
so sayeth Lake Speed Jr & an entire boatload of tribologists.

Turning fan temps down should increase oil pressure - oil pressure goes down as temp goes up.

 

[thefrey]

What you're experiencing is completely normal for your setup. Removing the oil pressure overflow valve in the oil pan removes the topline oil pressure limiter. Close to 80 psi cold and 25 psi idle hot are exactly where they should be. Oil viscosity changes with temperature.

I would warn you not to let the oil pressure exceed 80 psi, as you don't want to damage any oil seals. I am in the same boat as you, and when it is below 50 degrees here, I always remote start the truck and let it idle for at least 10 minutes, before moving it. And, when I do move it, I watch the oil pressure gauge very closely, and I baby the truck/motor rpm's so as not to exceed 80 psi. Once the oil warms up, and gets below 70 psi, then I'm ok to go without limitations.

I am curious, though, why are you running 10W-40 motor oil, when the published motor oil spec is 5W-30?

I was thinking about this, isn't there a relief spring in all of the oil pumps that will relieve pressure over a certain value (depending upon what spring you have)? I would think that there is a limit that it might stop at 85psi or so instead of climbing indefinitely.

I am especially curious because I have to get on a 65mph highway early in my drive and the on ramp is short so I gotta give er' the beans

 

[builds4christ]

I would say that's pretty normal. Nothing big to worry about imo.

I used to get 15psi hot idle, 28-32 cruising, and 45 cold start. After a new melling HV pump and DOD delete I get 60-70 psi cold start and higher when cold cruise, 25psi hot, and 42-45 cruising. I have 225k and some change right now. I am running 5w30.

I like the profile pic FYI. Would love to hear more about it.

Thanks for the tips @thefrey ! I'm super happy I made this post because I'm feeling better about this truck as I read, haha.

Thanks for the compliment on the profile pic! It's my side ministry/business. I try and use my mechanical skills to help those who either can't pay for repairs or need to pay significantly less. All to the glory of God because He's given me the skills and provided for me and my family all this time! So I guess I'm trying to pass it forward.

@Joseph Garcia thanks for the info brother! I'm running slightly thicker oil to account for larger clearances since the engine has a ton of miles.

I do that with all my aging engines. I don't go too extreme, generally, but most of my blocks have been iron, so I haven't needed to. This is the first aluminum block I've had that's swung so dramatically after it warmed up haha.

 

[builds4christ]

5W30 is fine. I get why people go to 10W40 when the spec is 5W30, ok, whatever.
Solid NO to Lucas. Choose the right motor oil (Valvoline Restore & Protect 5W30, just an opinion), change it early / often enough, never need additives,
so sayeth Lake Speed Jr & an entire boatload of tribologists.

Turning fan temps down should increase oil pressure - oil pressure goes down as temp goes up.

I'll have to check out Lake Speed jr! The only additive I've ever used was Lucas, namely because of the little demonstration dohickey sitting on top of the orielly counter .

I like the idea of the oil staying in places up top.

But I am curious about this so I'll check it out. I already bought the credits for the truck, so I'll hptune the temps down.

Thanks for the input!

 

[Marky Dissod]

... only additive I've ever used was Lucas, namely because of the little demonstration dohickey sitting on top of the o'reilly counter.

If you stare closely at it, you'll notice that Lucas lets the oil develop air bubbles, which made me nervous, so I avoided it.
(Other thing that made me nervous was when I recently stared at it again, and noticed I need reading glasses, gottdamnt!)

 

[Scrappycrow]

... or maybe a quart of Lucas?

I see someone beat me suggesting Lake Speed's videos to you!

Unless you understand the specific chemistry of the oil and specific chemistry of an additive, it's best to not use an additive. You could easily end up unbalancing the chemistry and end up with way too much in one area, or end up with the the oil and the additive chemistry canceling each other out.

Overall, the use of additives is outdated, so if you're basing this on anything like "I've done this for decades" or "My dad/grandpa told me to use them," you have to banish that way of thinking and update yourself to modern knowledge.

 

[SpareParts]

Never us a additive in my opinion. 10w 40 is perfectly acceptable in a higher milage l92 because of higher clearances especially in the summer months.
Why run the engine cooler?

 

[Marky Dissod]

I see someone beat me suggesting Lake Speed's videos to you!

It's just a roll of the dice. Besides, you got me into Lake Speed Jr.

Unless you understand the specific chemistry of the oil and specific chemistry of an additive, it's best to not use an additive.
You could easily end up unbalancing the chemistry and end up with way too much in one area, or end up with the the oil and the additive chemistry canceling each other out.

I've always wondered what would happen if I were wacky enough to mix 1Qt of each of the following:
Valvoline Restore & Protect 5W30
Pennzoil Platinum 5W30
Quaker State Full Synthetic 5W30
Mobil1 Extended Performance High Mileage 5W30
I've yet to decide which would be the 5th motor oil. Point is to mix 'em up and see what happens. Do they cooperate, or not?

Overall, the use of additives is outdated, so if you're basing this on anything like "I've done this for decades" or "My dad/grandpa told me to use them",
you have to banish that way of thinking and update yourself to modern knowledge.

Motor oil used to not be synthetic. Back then it might've even made sense to use CERTAIN additives.

Why run the engine cooler?

Motor oil does what it does better between 212F & 248F, so that H2O can be vaporized before it reacts with fuel washdown to form acids.
ATF does what it does better between 176F & 230F. As it gets hotter it gets thinner. They're not just lubricants, they're literally meant to keep things from touching.
Typically motor oil temp and ATF temp are NOT measured at the hottest possible spots, but at the easiest spots to mount sensors,
meaning that some of the oil / ATF is actually hotter than indicated.

 

[builds4christ]

Wow you guys are great! Thanks for all the good info. Seems like I've got a lot to think about!

 

[SpareParts]

Why run a cooler thermostat?
Seems to me running a cooler thermostat would be detrimental. Running to cool the ecu thinks it's not up to operating temp and is always trying to get up to it's programmed operating temp range that GM programming wants it to be.

 

[Marky Dissod]

Why run a cooler thermostat?
Seems to me running a cooler thermostat would be detrimental. Running too cool the ecu thinks it's not up to operating temp,
and is always trying to get up to its programmed operating temp range that GM programming wants it to be.

'Operating temp' is a temp window, not a specific integer. An ecm tune accounting for the cooler thermostat would work better of course.
So long as coolant gets hot enough to let O2s make corrections, and to let the CAT OverTemp bit enable (if desired),
only real penalty for staying on the cool side of GM's intended temp window, is -2 or -3 MpGs, which is offset by more longevity / greater durability for hard parts.

 

[mikez71]

I went with a Motorad 174 t-stat because my new OEM t-stat was sometimes not opening until 203F.
My Motorad 174 opens around 186-188 iirc..

I tried lowering the fan turn on to 194, but the fan would run way too often.
Stock fan comes on at 201F, currently set at 199, which acts normally.
Might be able to go down a 1 or 2 deg more? But more than that will likely be cycling too much..

I can hold 188deg if cruising on a cool day. But in the heat, it's always 192+.
(192 being the stock lower limit when cooling fan turns OFF)
Idling on only a warm day, temps rise from 192 to 199 in ~5 minutes. (guestimate)

So truth be told, it's not a whole lot of extra headroom..

@ 194F, 0 timing is pulled.
@ 212F, 3 degrees of timing retard.
So around 200degF, 1 degree of timing retard.
And around 206degF, 2 degrees of timing retard.

 

[Marky Dissod]

Note that the temp cited for a thermostat is when it BEGINS to crack open, it is fully open at a higher temp than cited on the packaging.

 

[builds4christ]

Got you guys.

I've got the ecm unlocked with HP tuners, but it isn't a simple on/off setting in my OS. it's a gradual fan control setup and the temperature tables aren't modifiable, only the percentages of desired fan at each temp step.

So it's a "Desired % vs ECT" setup, unfortunately, and the lowest temp you can modify the % is at 192 degrees. Unless any of y'all know hot to force the temp change!

I don't want it to run too cool, but would like it to stay between 190 and 195.

 

[mikez71]

I've heard you can't change the temp tables, UNLESS you convert it to 2 bar OS..
Not sure what all is involved (will need a new MAP sensor I'm guessing, looks like you need to fill in VE map, and will probably want some fine tuning)

BTW, you need to update your signature to include your new Yukon!