2001 Chevy Suburban Low oil pressure only at idle

Hi stensrude. Welcome to the forum. All three of those are possibilities. If the pickup screen is partially blocked, pressure will be low when the engine is first started and is still cold and the oil is thicker. Pressure will be higher at idle if the problem is related to bearing wear. The pressure will also go up, if bearings are the cause, if you use a higher viscosity oil or if you add a "viscosity index improver" such as STP. The additives only do the same thing as using the higher viscosity oils.

The clue too against the pickup screen being blocked is if pressure goes up when engine rpm goes up. That suggests higher volume overcomes the higher than normal internal leakage past the bearings. A blocked screen won't allow a higher volume.

Caradiodoc

If the pressure was already low at startup when the engine was cold, I'd be leaning more toward a worn oil pump. It's hard to make a judgement call based on mileage because neither the pump nor the bearings should show excessive wear yet. The place to start is by insecting the crankshaft and connecting rod bearings. That's really not a very serious undertaking. It just requires draining the oil and removing the oil pan. If excessive clearance is found, technically the proper repair is to remove the crankshaft, have it machined and polished, and install matching under-size bearings. But removing the crankshaft involves removing the engine or transmission, so a lot of people just install new bearings with generally positive results. If simple bearing wear is the cause, oil pressure will be restored. If a bearing is "spun", meaning it has a rough, ground up surface, the crankshaft journal will also be severely damaged, and you'd be hearing banging noises too.

If bearing clearances are ok, put the new oil pump in. They are relatively inexpensive and provide cheap insurance. Be sure to insect the pickup screen for looseness.

Since the STP helped, go with a higher viscosity oil at the next oil change. You should not have to use an additive at every oil change as it only provides the same increased thickness the higher weight oil provides. You might also try a straight weight oil such as 30W or even 40W. These are not good choices for cold winter climates because they can cause hard starting due to low cranking speed, and it can put added stress on the shaft for shaft-driven oil pumps. I've only read about those shafts breaking a couple of times but why risk it?

Caradiodoc

Can I move in with you? I live through Wisconsin winters!

You can tackle the bearings if you're mechanically-inclined. Be sure to put the caps on with a torque wrench. It will be helpful to have a service manual. I'm pretty linited on what I have for GM. What little I do have is not original so there's a chance the torque specs could be wrong.

Do you know how to use Plasti-gauge? Parts stores or engine machine shops that sell it can show you how to use it.

You might want to look at (examine) a new oil pump first. It used to be a heavy cast iron square block that bolted onto the bottom of the engine, but a lot of engines have been redesigned using a big aluminum plate that bolts onto the front of the engine and is run by the crankshaft snout. To change this style, it is usually necessary to remove a few of the front oil pan bolts so having the pan off already makes it easier. This style pump also requires removal of the timing chain. Due to valve spring pressure, it is common for the camshaft to turn a little when the chain is removed, so be sure you see where the timing marks are or mark them for future reassembly. Hopefully your pump is still on the bottom of the engine. That style is a lot easier to replace.

Caradiodoc