2000 Chevy Suburban Oil Pressure Fluctuates

Tiny
BARRY-WALKER@INSIGHT
  • MEMBER
  • 2000 CHEVROLET SUBURBAN
  • V8
  • 4WD
  • AUTOMATIC
  • 170,000 MILES
I have a Chey Suburban with a 5.3 liter V-8 that has 170,000 miles on it. Recently the oil pressure has started fluctuating. I have already replaced the oil sending unit and that did not fix the problem. The pressure normally varies between 40 and 60 psi. The fluctuations mainly occur when the engine is idling - the needle on the oil pressure gauge jumps around very quickly at idle. When the engine rpm is increased the oil pressure increases to about 60 psi and pretty much holds steady. Are the fluctuations an indication of a potential problem with the oil pump or could it be the oil pump inlet screen clogged in the oil pan (oil pan has never been dropped and cleaned)? If the oil pump inlet screen is clogged up shoudn't the fluctuations in oil pressure occur at all rpm ranges? Should I even be concerned about this?
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Wednesday, August 19th, 2009 AT 9:40 PM

7 Replies

Tiny
MHPAUTOS
  • EXPERT
Hi there,

Thank you for the donation,

My first thought would be a sticky oil pressure relief valve, the fluctuation at low engine speed would tend to indicate this, have you tested the oil pressure with a mechanical gauge to be sure that you are actually chasing a pressure related problem?

Mark (mhpautos)
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Wednesday, August 19th, 2009 AT 11:27 PM
Tiny
BARRY-WALKER@INSIGHT
  • MEMBER
I have not tried to use a pressure gauge yet in place of the oil sending unit. Is there a way to hook up a gauge to the oil filter mounting surface which I think would be easilier than trying to hook up the gauge to the oil sending unit port which is difficult to get too. If the problem is a stickiy oil pressure relief valve then is there an easy fix for that (short of removing/replacing the oil pump)?

Thanks
BRW
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Thursday, August 20th, 2009 AT 7:00 PM
Tiny
MHPAUTOS
  • EXPERT
You will have to hook it up at the sender unit point, I will look but normally this will be at the pump in the sump.

Mark
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Thursday, August 20th, 2009 AT 7:35 PM
Tiny
BARRY-WALKER@INSIGHT
  • MEMBER
If the relief valve on oil pump is sticking then what is the solution to fixing?
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Thursday, August 20th, 2009 AT 8:41 PM
Tiny
MHPAUTOS
  • EXPERT
Replace the pump and pressure relief vale as a unit, I will have to check first if the valve is part of the pump Assembly, I don't have access to Mitchell 1 just yet so if I have problems I will pass it on to a Mod that can look into this for you.

Mark (mhpautos)
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Thursday, August 20th, 2009 AT 8:47 PM
Tiny
MHPAUTOS
  • EXPERT
Just an update,

As I will now be away from the computer that I have Mitchell 1 access from for a few days, I have forwarded your question and these post to our No 1 Mod, I am sure that he will pick this up and assist you with this question, I will keep an eye on the progress and add what I can if required.

Mark (mhpautos)
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Thursday, August 20th, 2009 AT 8:58 PM
Tiny
RASMATAZ
  • MEMBER
When was the last oil and filter change?

To actually know what's happening with the oil pressure -you have to hook up a mechanical gauge to where the oil pressure switch is and read the pressure if normal replace the oil pressure switch out of calibration -abnormal could mean an oil pump and engine bearings-sludge/debris in the crankcase could be clogging things up in there that's the pick tube screen and oil filter-

If the relief valve on oil pump is sticking then what is the solution to fixing? Replacement needed here.

I strongly recommend an engine flush and go from there.

When the oil leaves the pump, it passes through the filter before going on to the bearings and oil galleys. All filters create a certain amount of resistance to flow that increases with the rate of flow. But the amount is not much, typically only a couple of pounds. But as the filter becomes clogged with debris, the restriction created increases. Eventually the point may be reached where no oil will pass through the filter element. So to prevent such a blockage, a pressure relief valve located in the filter or where the filter mounts to the block is designed to open if the pressure differential across the filter exceeds a preset value (typically 5 to 40 psi). This allows the oil to bypass the filter and keep on flowing. But the engine's oil pressure will be reduced to that of the bypass valve. Replacing the plugged filter will solve the problem.
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Thursday, August 20th, 2009 AT 9:51 PM

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