Oil pressure

This article is primarily for the 4.8 through 6.2 liter
motors. Oil pressure starts from oil pump. The oil
pump pulls oil from the oil pan through the oil
pickup tube the distributes the oil throughout the
engine. Think of the oil flow like a water faucet.
When water runs out of the faucet there is very
little restriction, thus very little pressure. If you
restrict  the flow with your hands it will try and
squirt out wherever it can. This is a simple way of
describing an engine oiling system. The seals
,gaskets and bearings in an engine are what keep
the oil from squirting out causing oil pressure loss.
Good gasket,seals and bearings are an important
part of the diagnosis process. So let's start with
breaking this down in about three parts. 1st the
suction part. The oil pump pulls oil from the pan
through  a metal tube with a seal and a screen on
it. If the screen is plugged the pump cannot get the
oil it needs. And if the seal is defective then it pulls
air inside the pump and reduces pressure. Gm has
had issues in the past with this seal failing.
Difficult to diagnosis without disassembling. The
screen however can be checked through  the drain
plug hole with a flexible camera. Not a very
expensive tool anyone can purchase one and most
shops will have one. 2nd the pressure part and
most difficult part to diagnosis. The oil pump
pushes the pressure into the oil filter and up the
engine to oil  pressure gauge. The oil travels down
the engine from the oil pump through the oil pan
gasket into the filter and back up the oil pan gasket
to the oil Guage sender. This oil pan gasket has
two rubber orings. If they fail oil pressure is lost.
They can either leak external whereas it can be
seen or they can leak internal and cannot be seen.
From the oil Guage , oil travels to a number of
seals and bearings. The oil pump is capable of
pushing about 120 lbs of pressure to the engine.
This is really to much pressure but the excess
amount of pressure is regulated by a spring and
valve in the oil pump itself. The valve and spring
will deliver about 60 lbs of pressure to the engine
and send the excess back to the oil pan. They do
this because parts wear and when they do it drops
the pressure. This is how the engine maintains a
constant flow of oil pressure. Even if there are
small oil leaks either internal or external such as oil
leaks or worn bearings and internal parts , the oil
pump has enough reserve pressure to maintain a
steady pressure to the engine. 3rd part is locating
the source of low oil pressure. I will list in order the
items most common, least expensive and least
evasive to check when trying to diagnosis oil
pressure loss.
1 oil sender and if it is a fuel management engine
then also the screen below oil sender, easiest to
change and  most common to fail.
2 oil pickup tube screen. Check it through drain
plug hole with camera to see if the screen is
plugged.
3 oil pan gasket. Orings built into gasket shrink or
break causing external leak around oil filter or
internal leak showing no signs of leaking but
sending oil pressure back to inside of oil pan.
4 camshaft thrust plate. Most common part I have
had to replace. Located behind camshaft  gear.
Has a small seal built into this plate which goes
flat and allows oil pressure to drop especially when
warmed up. Requires removing water pump,
crankshaft pulley and front timing cover. 4 bolts
hold it on behind camshaft gear.
5 oil pump pickup tube oring. In order to replace
the oil pickup tube oring the oil pan and front
timing cover have to be removed at the same time.
6 all this being said this diagnosis is for gm
engines with oil pressure loss but otherwise they
run normal. If you have abnormal noises, knocking,
or running issues those will need to addressed
first.