Skibadc

Hello Experts - I'm new here but have been trolling for help / reading over the last months.

2009 5.3L Chev engine, AFM, VIN 3, about 285,000 km on motor

Fast recap: Had problems with low oil pressure, failed lifters, etc., pulled engine, did complete rebuild (meaning pistons out, to rebuild shop, clean, hone measure to spec, new CAM bearings install, new CAM shaft GM std, heads cleaned, surfaced, valve seats redone. On rebuild new rings, new valves, new lifters, new crankshaft bearings, new misc parts, seals, and the like. New Melling higher pressure oil pump, new o ring, new oil pressure relief valve, (and added the deflector), replaced oil pressure sending unit and screen (twice), new oil filter.

Start up procedure followed per spec. Started right away.

Problem - normal oil pressure for first few minutes, but as soon as motor reaches normal operating temperature, the pressure drops to 10 or less, then goes to zero with warning on dash to shut down engine.

I've confirmed pressure at oil pump is is normal range (anywhere from 30 to 50 pending rpm) with manual gauge. Oil pressure at top end is reading much lower, anywhere from 5 to 15. Both manual and electrical gauge are consistent / match. Incidentally, I've confirmed oil sending unit is working measures 12.95 micro ohm.

engine run smooth initially on start up, but once oil pressure drops then there is ticking due to starved lifter / no oil.

It seems there is a problem between the oil pump and the top end - I am at a loss....
oil pressure relief valve was changed - thinking originally that it was stuck 'open', and oil galleys, oil cooler lines and radiator blown out out with air. on the third time pulling engine! The SAGA part.

sorry long post, lots of details. Happy to post more if needed :-)

Gumby22

The only components between the pump and top end are the filter, cooler and relief valve.

First try changing the filter, regardless of how new it is.

If that doesn’t change the pressure, I’d recommend temporarily bypassing the oil cooler circuit. If pressure improves, there’s likely a restriction in the cooler.

If it still doesn’t improve, either the relief valve is at fault or there’s a restriction between the relief valve and the top end.

Skibadc

Thanks Gumby,

I have installed a new oil relief valve (GM part and deflector) in oil pan.
I changed oil filter as well to AC Delco FP46 (stock)
I blew out all oil lines at same time (meaning from top to oil filter, from oil pump to oil filter, the hoses for oil cooler, and the radiator / oil cooler).

Just ran this afternoon with no valve covers on - no lifter issues, good movement, BUT NO OIL at all from push rods over the top of rockers.

something causing oil pressure to not stay stable / fall after normal temperature hit.

head scratcher - engine coming out again I think!

Gumby22

Then you’ll need to verify bearing clearances. It sounds like the pump is working, and if it’s unlikely the relief valve is at fault and there’s no restrictions in the galleys, the only thing left is the bearing clearances. If they’re excessive, oil pressure can’t properly build, especially at operating temperature.

One other test is to replace the oil with a heavier weight, such as 15w40 (diesel oil) or straight 40 or 50 weight. If pressure improves with a heavier oil, the bearing clearances are most likely to be at fault.

Here’s an oil flow diagram. The cooler circuit would be in series between the filter and block.

Aeromech777

I had the same problem, mine was the dreaded Oil pick up tube o-ring. 12 hours under the truck for a 50 cent oring. Changed the Pressure switch, screen, etc...
When I started the I truck had the exact same thing, Then I read in a chat somewhere that certain oil filters will cause the problem also. So I ditched the Fram. and replaced it with the AC Delco Gold #UPF48R (rockauto has them for 7.79) and I have not had a problem since.. Here's a good article good luck on it. "There is a SI bulletin from GM, #PIP5276D which tells you if you run into this problem, it will also set a code P0521,to upgrade to a UPF48R filter. "
https://bobistheoilguy.com/forums/th...-pf48e.286907/

dpieroni3

should also check the valve lifter oil manifold (VLOM) for a leak.