Low oil pressure....sometimes

I am very interested in what you find changing out the o-ring. Mine is basically doing the same thing. Repeatable low oil pressure on low engine temps. Just the opposite of what it should be. Been watching for about 6 months now. The oil press will drop below 20 psi until it hits operating temp at 210 F. Once at operating temp, no problems, always 30 to 40 psi depending on rpm. Which makes me think an o-ring problem. It may be swelling up with increased temperature. Until it warms up, I am always putting it in nutural at red lights just to keep it above 20 psi. Once at 210, no problems. Also no problems if it cools between daily uses (hours between uses). But if it's days or maybe even 24 hours, back to low pressure issues. Very repeatable issue and would like to get it fixed. The Chevy place is clueless !

Reebok59 said:

I am very interested in what you find changing out the o-ring. Mine is basically doing the same thing. Repeatable low oil pressure on low engine temps. Just the opposite of what it should be. Been watching for about 6 months now. The oil press will drop below 20 psi until it hits operating temp at 210 F. Once at operating temp, no problems, always 30 to 40 psi depending on rpm. Which makes me think an o-ring problem. It may be swelling up with increased temperature. Until it warms up, I am always putting it in nutural at red lights just to keep it above 20 psi. Once at 210, no problems. Also no problems if it cools between daily uses (hours between uses). But if it's days or maybe even 24 hours, back to low pressure issues. Very repeatable issue and would like to get it fixed. The Chevy place is clueless !

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I was also a little disappointed that the shop I took it to didn't have a more definitive answer than "well, it is above the minimum spec", but I decided to go ahead and have them replace the o-ring. They are doing the work today, so hopefully I will see normal oil pressures when I get it back.

Hated to let someone else work on it, I prefer doing my own repairs, but I just don't have the time right now. Since they are going to have to drop the front axle, I gave them the axle seals to replace that I have had sitting around for a couple of months too.

Reebok59 said:

I am very interested in what you find changing out the o-ring. Mine is basically doing the same thing. Repeatable low oil pressure on low engine temps. Just the opposite of what it should be. Been watching for about 6 months now. The oil press will drop below 20 psi until it hits operating temp at 210 F. Once at operating temp, no problems, always 30 to 40 psi depending on rpm. Which makes me think an o-ring problem. It may be swelling up with increased temperature. Until it warms up, I am always putting it in nutural at red lights just to keep it above 20 psi. Once at 210, no problems. Also no problems if it cools between daily uses (hours between uses). But if it's days or maybe even 24 hours, back to low pressure issues. Very repeatable issue and would like to get it fixed. The Chevy place is clueless !

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This sounds more like a tired motor liking higher viscosity oil. So when she heats up, the oil is now at 30 weight and the pressure goes up then cold at 5 weight.

swathdiver said:

This sounds more like a tired motor liking higher viscosity oil. So when she heats up, the oil is now at 30 weight and the pressure goes up then cold at 5 weight.

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Not sure that's fair to say. Oil doesn't change from a "thin" viscosity when cold only to thicken at operating temp.

5w-30 just means it's a 30w at operating temp, but the oil when cold, will not thicken at the same rate as an SAE30. It'll maintain some better flow characteristics between a 5 weight and a 30 weight, but it WILL be many many times thicker when cold.

See this graph here



Fun point of note; see how the viscosity vs. temperature change is shallower with the 5w-30 as opposed to the 10w-30? If you were to continue to plot this function above 100c and look at it closer, the 5w30 would actually maintain a thicker viscosity than the 10w30 as temps rise. Essentially the higher the viscosity index of the oil, the shallower that temp vs. viscosity slope is. Not as thick when below 100c, not as thin above, with 100c being the intercept point. It's why I always recommend oils with a good viscosity index, and never subscribed to the "you need to run a 10w30 for hot weather because it's thicker" ideology - it's just wrong. There are some cases where you might want that, but trying to argue temps and viscosity isn't it! I'd run 0w30 year round. From -10 to over 110 degrees. Just switched to a 0w40 due to availability and pricing but that's a different discussion

If I graph up some theoretical oils:

Note that the 0w30 doesn't get as as thick when cold, but still quite thick




If we go really cold, you run into some pretty substantial differences. Note the viscosity numbers at the bottom, knowing that both oils are supposed to be 11cst@100c

The 0w30 is nearly 500 times that value, whereas the 10w30 is over 1000 times that!



If we change gears and look at higher temps, you get some rather interesting results. The oil that's thinner when cold is now... Thicker when hot? That goes back to the "slope" description I was using above. That 'thin' 0w30 actually does a better job at resisting thinning as temps go up.



Realistically, you're talking about 0.1 to 0.2cst differences. In the engine, that's not enough for it to care or really notice. BUT it is there. And I think provides enough into to frame the argument I'm making.

So....got the Tahoe back last night from the shop, and the o-ring solved my low oil pressure problem. However, next time I think I'll bring the pan gasket with me. $141 for a pan gasket??? That's ridiculous, shouldn't have been more than about $35. Also, my backup camera is no longer working, although I really can't see any way to blame them for that. Just a coincidence I think.

What a relief. It makes sense that it was the O ring because when the oil was cold and thick, the pressure was low. I think the bad rubber became pliable after it warmed up.

Good thing you didn't wait for idle pressure to go "out of spec". Now she's good for another 200 k.

DougAMiller said:

So....got the Tahoe back last night from the shop, and the o-ring solved my low oil pressure problem. However, next time I think I'll bring the pan gasket with me. $141 for a pan gasket??? That's ridiculous, shouldn't have been more than about $35. Also, my backup camera is no longer working, although I really can't see any way to blame them for that. Just a coincidence I think.

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Now I'm wondering why your O-ring testing didn't reveal this. If the testing methods aren't reliable, it'd be helpful for others to know why and what can be done.

I was wondering the same thing about the o-ring test. I highly suspect my low oil pressure issues are due to my O-ring but if possible, I would like to confirm with a test before dropping the oil pan. Is the recommended procedure 2 qt overfill plus incline if possible? And has it been used reliability by others? Sounds like it really didn't work for Doug.

Well, the backup camera was just a bad ground, all better now.

iamdub said:

Now I'm wondering why your O-ring testing didn't reveal this. If the testing methods aren't reliable, it'd be helpful for others to know why and what can be done.

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Good question. From what I've read either the overfill method OR a steep incline is recommended to test this. However, when the overfill didn't change anything I put it nose down as much as I could and still nothing. So, I would have thought that even if I didn't do either one of them quite enough, combining them should have submerged the o-ring.

I guess someone needs to fill one with the timing cover off so they can visually confirm how many quarts it takes to submerge the o-ring.