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Mark, ASE Certified Technician
Category: GM
Satisfied Customers: 847
Experience:  34+ yrs Dealership Exp. - Fully State & ASE Certified - GM Master & GM World Class Tech
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2005 suburban: oil pressure..changed oil..he put in a new oil pump

Customer Question

i have a 2005 suburban that suddenly lost oil pressure. i changed oil and filter, did n t cure the problem. i took it to a mechanic,he put in a new oil pump. this has not corrected the problem. the lifters unload at an idle. when the rpm is increased the oil pressure increases enough to fill the lifters. what else could be restricting the oil flow. i think the motor is a 5.7 v8 and has 118,000 miles. the oil and filter has always been changed at 3,000 mile intervals. need help! charles vrska [email protected]
Submitted: 6 years ago.
Category: GM
Expert:  Mark replied 6 years ago.
Greetings and welcome to Just Answer. My name is Mark.

Only making a suggestion here because I have been here and seen it done. There is an 0-ring that seals the pick-up screen to the oil pump. It is VERY IMPORTANT that this 0-ring is installed correctly, or the exact situation you are encountering will happen. At an idle, the oil pump will just suck air and you will lose oil pressure. Once you pick-up the idle, the oil pump spins faster. Yes, it is still sucking some air, but it will pick-up the oil too. Now the lifter noise goes away until you bring it down off idle.

I know you start out your post with your vehicle losing oil pressure suddenly, and then finish up with the oil pump being replaced, but I have seen these o-rings split and fail on an otherwise normally running engine.

I am going to assume your mechanic took an oil pressure reading BEFORE he replaced the oil pump. There is a lot of work to replacing the oil pump on one of these, and if your mechanic is not familiar with installing the pick-up screen correctly, he could have repaired your original issue, and created another.

I have seen these 0-rings fail and create the kind of issue you're talking about. The repair is not the oil pump, as much as it is the pick-up screen o-ring. If initially the mechanic takes an oil pressure reading and it is low or non-existent, the first step is to remove the oil pan and then remove the pick-up screen. If one finds the 0-ring to be the issue, then there is no need to replace the oil pump, as it requires removal of the engine front cover.

Below, I have included the repair and pictures of the pick-up screen and pump. I would ask your mechanic if he indeed remembers installing the 0-ring SECURELY and CORRECTLY. I would then put an oil pressure gauge on the engine and verify you have no oil pressure. I know by your description with lifter noise and such, you do not, but you want to make sure.

If you had an engine bearing issue, the characteristics usually are different than what you are describing. Oil pressure may come up a little bit upon RPM increase, but lifters don't normally bleed down as much as you're indicating. Oil pressure is created and maintained by bearing clearance. As engine bearings wear out, oil passes through more easily and thus, lower pressure. With worn out bearings, there usually is some engine bearing noise associated.

I am not saying you don't have more serious engine issues, ... I am only stating by what I am reading here, it sounds to me like the o-ring issue. It is worth a check see.

Oil Pump and Pick-up Screen

Removal Procedure

    Object Number: 647800  Size: SH

  1. Remove the oil pan.
  2. Remove the engine front cover.
  3. Remove the oil pump screen bolt and nuts.
  4. Remove the oil pump screen with O-ring seal.
  5. Remove the O-ring seal from the pump screen.
  6. Discard the O-ring seal.

  7. Object Number: 683798  Size: SH

  8. Remove the remaining crankshaft oil deflector nuts.
  9. Remove the crankshaft oil deflector.

  10. Object Number: 64281  Size: SH
  11. Remove the oil pump bolts.
  12. Important: Do not allow dirt or debris to enter the oil pump assembly, cap end as necessary.

  13. Remove the oil pump.
  14. If required, clean and inspect the oil pump.
Mark and 2 other GM Specialists are ready to help you
Customer: replied 6 years ago.
have completed your suggestions, problem still not solved. any other ideas? charles
Expert:  Mark replied 6 years ago.
Hello Charles. We need to make sure our communication is correct.

Please verify that I understand from your original post. You have no oil pressure at an idle. When you rev up the engine, your oil pressure increases and the lifter noise goes away.

Is this correct?

Also, up to this point, you have a NEW engine oil pump and the 0-ring is intact?

Is this correct?

I will get back to you tonight when I know I fully understand our communication here. I just want to make sure I haven't missed anything and there hasn't been any new developments since your original post.

Thanks, Mark
Customer: replied 6 years ago.
every thing is properly connected but still have the same problem with oil pressure. the next thing i will do is check the main bearings to see if they have failed for some unknown reason. Charles
Expert:  Mark replied 6 years ago.
Hello back Charles.

If you have a new engine oil pump and the 0-ring is in place, then you are right in checking the bearings. When oil is "forced" between two surfaces, pressure is creating. When there is no "restriction" (the clearance between bearing surfaces) then no or low oil pressure will exist.

Personally, I would be more concerned with cam bearings. Take a good look at the "lobes" of the cam also. I have replaced more chevy engines, and rebuilt more chevy engines in the past 5-7 years with cam and bearing issues more than rod and main issues.

Rounded off lobes, chips and pieces missing on lobes, severe scoring on lobes, and damage to the roller lifters, are all possibilities. If you are just removing the engine oil pan, look carefully up through the block and inspect the cam. Turn the engine over to be able to see all you can. You won't be able to see number 1 lobe, and that threw me for a loop on one occasion. I have a strange noise and erratic pressure. All rod and main bearings looked good, and the cam looked good.

Had it torn partially apart too many times and too much theory. It was time to remove and dis-assemble. I found the number 1 cam lobe damaged and cam bearing scored.

Remember, if you do find cam bearings scored to a point where they have spun in the bore, you'll need an engine. GM doesn't recommend and I don't think they make "over-sized" cam bearings. If the cam bearings are just scored, and they haven't spun, you can replace the bearings and cam.