Random oil pressure fluctuation

[Jon Goyette]

Here's an issue that has me stumped. 2000 Silverado, 4.3, 200K mi. Truck runs great, no oil consumption. I have a very random oil pressure fluctuation, normally I have 40 psi (+ or - 5psi) pretty steady, not affected by rpm or temp. about 20,000 mi. ago I started getting a lifter tick on start up accompanied by crazy fluctuation in oil pressure relative to rpm ( 15psi at idle and 60+ at 3500) It will do this for maybe a week and then stop....no tick and steady oil pressure again. Truck has always had regular oil changes with quality oil (dino) and a Wix filter, I've tried Lucas oil additive, Marvel, different viscosities between 10-30 and 15-40 nothing makes it worse or better. Seems to go away by itself and then return completely at random. Sometimes it will go 5k with no issues, other times maybe 2k. Not affected by oil changes or mileage...just comes and goes. Always lifter tick and oil fluctuation....tick goes away and so does crazy oil pressure. WTF is going on?

[Jstevens7700]

Maybe the oil pressure sensor? Not very hard to change, might be a good start and maybe step two would be evaluating the instrument cluster.


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[Jon Goyette]

Right, that doesn't explain the lifter tick associated with the pressure fluctuation though. If it was just the sensor I don't think there would be a mechanical symptom too....

[Jstevens7700]

My lifter taps every now and then. I mix lucas heavy duty engine oil stabilizer a quart or two to 4 quarts of oil and it seems to quiten it up. Usually taps when i need an oil change.

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[RivGuy]

To fix it properly, that is not using a thickening additive in the oil, would be to replace the lifter(s).

If it's possible to determine the lifter that is failing and giving you the interment ticking and the oil pressure drop you could cheap out and just replace that lifter.

But the smart move is to replace them all, especially with the mileage you have on the engine.

Lifters are inexpensive in the big picture and you'll get a lot more miles from the engine using the factory recommended oil after replacing them.

Good luck.

[Jon Goyette]

I can see a bad lifter causing a drop in pressure, but would it cause an increase too? When the engine is operating in "no tick" mode, oil pressure tops out at 45psi and is steady regardless of rpm. In "tick" mode, oil pressure increases to 65 at higher rpm and drops to 15 at idle. You think a bad lifter is the culprit? Not trying to be a dick here, just want to verify the issue before replacing parts. Thanks for the input.

[swathdiver]

18 minutes ago, Jon Goyette said:

I can see a bad lifter causing a drop in pressure, but would it cause an increase too? When the engine is operating in "no tick" mode, oil pressure tops out at 45psi and is steady regardless of rpm. In "tick" mode, oil pressure increases to 65 at higher rpm and drops to 15 at idle. You think a bad lifter is the culprit? Not trying to be a dick here, just want to verify the issue before replacing parts. Thanks for the input.

Jon, is that 4.3 based on the LS Gen III motor?  It could be the o-ring for the oil pump's pick up tube.  But, I would think that would cause the pressure drop and fluctuate, not get higher.  I'm guessing here but I think that if the pressure goes up and a lifter starts ticking, you are getting a restriction somewhere that causes a loss of volume for a moment while the pressure is high.  If that is so, what parts inside an engine can cause that?  Does the motor have roller lifters, maybe one is moving slightly?  Oil pump gears moving out of position for some reason?  Debris or sludge in the oil pan restricting the pickup from time to time?

[newdude]

59 minutes ago, swathdiver said:

Jon, is that 4.3 based on the LS Gen III motor?  It could be the o-ring for the oil pump's pick up tube.  But, I would think that would cause the pressure drop and fluctuate, not get higher.  I'm guessing here but I think that if the pressure goes up and a lifter starts ticking, you are getting a restriction somewhere that causes a loss of volume for a moment while the pressure is high.  If that is so, what parts inside an engine can cause that?  Does the motor have roller lifters, maybe one is moving slightly?  Oil pump gears moving out of position for some reason?  Debris or sludge in the oil pan restricting the pickup from time to time?

 

Old 4.3 was Gen 1 350 based.  350 minus two cylinders.  The "Vortec" 4.3. 

[Jon Goyette]

James, Thanks for the reply. The 4.3 is basically a Gen 2 vortec, 5.7 flat tappet engine with 2 cylinders lopped off. My 1st thought was oil pump, pickup, tube or screen. but then I thought if there was a blockage it would have to be on the post pump side of the oiling system to cause the increase in pressure. This lead me to think it was the ticking lifter that was the cause, even though I can't really wrap my head around that due to the symptoms. Looks like I will dive into the lifters, probably about due to put a new spider on it anyway. Should probably pull the pan and go after the oil pump too just to be safe...and why not do a timing set and cam...but thats why I didn't want to get into it in the first place...

[sefiroxx]

Of running a thickening agent, then the pickup vacuum is unable to feed enough oil to raise pressure. Once the oil ages, pcks up moisture and thins out, the oil pressure will rise and the idle oil pressure problems come about.

The AFM needs 22+lbs to operate correctly