'05 5.3 oil pressure change

[hikerboy]

My '05 5.3 Z-71 has normally run about 45-50 psi while cruising down the highway at 55mph, turning about 1800 rpms (4.10 rear end).  Recently, the gauge is showing less than 40 (30-35) and at idle, it's at about 20 or less, which is also a drop from normal history.  I've owned it since new, changed oil religiously, and it's got 100K miles.  Recently had the oil pan gasket replaced, but I know that the oil pickup tube o-ring was not changed as it's not noted on my invoice (didn't know about that before doing some research)   Possibly an oil pressure sending unit? Gauge cluster was replaced a few years ago with an updated stepper motor design. 

 

Other than wishing I'd had the shop replace the pickup o-ring when I spent $475 to have the oil pan gasket replaced, any advice?

 

Thanks!

[muddkatt]

Hook up a mechanical gauge and see what the pressure really is. Proceed from there.

[CamGTP]

The filter screen if there is one for the oil pressure switch could have junk in it too.

[hikerboy]

No filter screen on the pre-AFM engines - - but I'll take it in and have it checked out. 

[hikerboy]

Update - - oil change, 5W30 Chevron Supreme and a new Purolator One oil filter....voila, back to normal/previous levels. I'm guessing the viscosity was poor on the old oil and perhaps a filter problem with the PF46E, but whatever the case, I'm happy now.

[Bill336]

Do you suppose the shop reused your oil or used an inferior oil?

[hikerboy]

Bill336, that's a good question - - It's a reputable shop, I'm guessing an inferior oil. I'm 1000 miles into the Chevron Supreme 5W30 and all is still good.

[Gagliano7]

Oil wouldn't affect pressure that much. I am going with a bad filter.

[Caroline Foister]

have a2011 later c  can 5.3 starting  pressure  isabou 40  once I warms up rips to 0 hangers oil pressure sensor  2x aftëf market then dealership  paŕf he check engine  light  comes on at Hut down an Inger beggings I poked o dealër th y Corey zaid ascending  unit now säys liftès or brain there  is no miss runs great wanting to harvest $2300 plus parts I can't afford can't get loan has 116k an babiëx oil change with synthetic  e Erykah 3 months or 3000 zàme filër qnd oil usèx sinë Brenda new Suggestions  please 

[swathdiver]

16 minutes ago, Caroline Foister said:

have a2011 later c  can 5.3 starting  pressure  isabou 40  once I warms up rips to 0 hangers oil pressure sensor  2x aftëf market then dealership  paŕf he check engine  light  comes on at Hut down an Inger beggings I poked o dealër th y Corey zaid ascending  unit now säys liftès or brain there  is no miss runs great wanting to harvest $2300 plus parts I can't afford can't get loan has 116k an babiëx oil change with synthetic  e Erykah 3 months or 3000 zàme filër qnd oil usèx sinë Brenda new Suggestions  please 

Probably need a new oil pump pickup tube o-ring.  Fill the engine with 8 or 9 quarts of oil and see if the pressure stays up.  If it does, that's your problem.