1998 4.3 shell 10w30~im wondering how the switch gets its pressure reading and from where. i know where the oil pressure sensor is located, but is it an oil passage or is it reading somewhere else. also i read that its a diaphram style, so i assume it just pushes the diaphram in and it gets its reading that way, is this true?

also how do worn engine bearings effect the readings? also what else can cause low/fluctuating oil pressure. a failing pump is obvious...and possibly the oil filter/weight of oil used.

im more more curious than i am worried right now, but sometimes at idle/warm motor, the needle will flicker between say 18 and 20psi pretty jittery, but for the most part it sits steady at 18 or 19psi(fully warm engine) while cruising the highway its a hair under 40psi. and while slowly accelerating its 40-42psi.

now this is a longshot and i might get laughed at, but can a rear main seal leak contribute to lower oil pressure? i guess no, but thought id ask since its oil leaking....

I'm aware that stock oil gauges are not the greatest, and that gm says 8 or 10 psi/1000rpm

 

The switch just reads pressure running through the oil galleys. They are just long holes drilled in the block that direct oil to the bearings. There are galleys all through the block. Any hole you see with a pipe plug in it is a hole left from drilling out oil passages.

That is most likely true and the oil pressure just has to overcome spring pressure on the opposite of the diaphram. The diaphram would then move and close a switch.

Worn bearings are going to allow oil to escape the bearing clearance easily. Notice how a garden hose has more "pressure" as you increase resistance to flow? The bearings create resistance to flow which in turn creates pressure. So as bearings wear the clearance increases and reduces resistance to oil flow. Increasing oil weight makes it more resistant to flow so it reads more pressure... but that is a band-aid fix at best.

In my opinion your pressures are fine as you said. That's what mine is reading on the guage as well.

Seals only keep the oil in the engine. They should not hold back any pressure and if so, something is wrong. I believe the average oil seal can only stand-up to about 10psi before blowing out. Oil seals generaly only leak due to wear of either the seal lip or the sealing surface or both. Or damage of course.