I have a 2003 Tahoe with 170k miles that has run like a top and has had Amsoil synthetic oil changed at 7-10k mile intervals. But I may have killed it...

My problems, in brief:

• Added instructed amount (8oz) of ATP leak-stopper to oil to hopefully stop oil pan gasket leak (great Amazon reviews), ran for 200-300 miles and noticed slowly declining oil pressure at idle, but not concerningly low. Pressure increased with RPMs to about 35-40psi. Called their customer service, they said it was fine to run in the oil until the next oil change. One day, low oil pressure warning light came on, so changed the oil, expected pressure to return to normal, no luck, still low at idle.

• Symptoms were and still are low oil pressure at idle once warm at about 15-20psi and the Oil Pressure Low light comes on

• Replaced the oil pressure sender with genuine ACDelco, no change

• Had the oil pan gasket and o-ring replaced, no change

• Changed to a much thicker Rotella 15w-40 diesel oil, takes longer to warm up and pressure to drop, but Oil Pressure warning still came on during the 10 mile drive after change.

• Upon that oil change, noticed a ferrous metal powder on the magnetic drain plug with only ~200 miles on previous synthetic oil, which has me very concerned. Truck has been parked for the last week since that 10 mile drive.

• No sewing machine noise or lifter tapping during idle with the low oil pressure.

As the thicker oil didn’t really change the oil pressure at idle, does that sound like a bad oil pump? Can bearings go bad that quickly with synthetic oil and only poor pressure at idle? Is there a way to determine if it’s bearings or oil pump?

I will be sending the oil sample to Blackstone for analysis to see if the metal is bearings or what. Will update with results.

 

I'd lean towards the pump first before I thought the bearings are the cause.

 

The LS oil pumps fail often? I thought these things were near bullet proof.

 

bearings wont leave anything on the plug, bearings are non magnetic, made out of metals like aluminum, zinc, manganese, tin, etc.

 

Everything will eventually fail. Oil pumps are a cause for concern on the earlier gen3 motors. my 02 has 167k on it, and the pump hasnt failed, but I have metal fuzz/slurry on the drain plug too.

 

Any way to diagnose bad oil pump vs bad bearings before I spend half a day putting a new oil pump on?

 

If its not knocking at any RPM, probably not bearings. If it has enough clearance to drop pressure that much, it has enough clearance to knock. IMO

 

I was gonna put that stuff in mine to hopefully stop the rear main leak. However, after reading numerous reviews of losing oil pressure i decided against it.

 

Yeah, steer clear! My wife's bone stock 2009 Tahoe dropped oil pressure too, but not to a critical level. And I only left that stuff in her Tahoe for two days before I changed the oil, but the oil pressure never returned to ~40 at idle, it's more like 30 now. And the stuff didn't slow or stop either leak

How's the '02 Tahoe treating you? Still running well?

 

I am guessing the stop leak caused the bypass in the oil pump to stick causing the low oil pressure. The engine may not be detrimentally hurt and you may be ok if you get the pressure back up.