Well I got into my truck today and before I started moving I looked at my oil pressure and its about 20... But when I start moving it goes to 40 but when I shift into R or D my RPMs drop down to past 1k for a second then its ok. But why is my oil pressure at 20 when its ideling? My friends cars are all at 40+ when they idel...help please

 

Did you check your oil level? If its low then it gauge will read low. Oil pressure is always lower at idle.
Possible problems for low oil pressure:
1) low oil level
2) bad valve seals
3) bad piston rings. ( do a compression test)
4) gauge not working properly.

These are the obvious, may have missed somethin.

 

Every vehicle is different. And every vehicle has different oil supply demands.

Low oil pressure for the 4.3L v6 according to GM is 8psi and this is where the newer trucks will simply not run if the oil pressure dips below this level. 20psi is plenty at idle and 40psi is more than enough when moving. My chevelle only has around 12psi at idle and 25-30psi at speed (30psi at 6000rpm), but that has a high volume (not high pressure) pump and everything is rather high on the clearances.

Low oil pressure should cause fluctuations if you are actually getting to oil starvation levels.
Bad valve seals and bad piston rings will lead to burning oil causing lower levels if not kept in check
Gauge could be off.

Main things that can affect the oil pressure (aside from low oil level causing starvation) are a weak pressure relief spring, clogged oil filter, and/or excessive bearing clearance on the crank mains, rods, or cam bearings. There are others, but I can't think of them right now.

Typically, long before the oil pressure will drop enough to do damage (if you are just loosing it due to bearing clearances), you will hear the lifters start to tap due to the hydraulic lifters using the oil pressure to pump up. If you are not hearing lifter tap, your pressure is fine.

What kind of oil filter are you using? What viscosity of oil are you using (5w30 or 10w30)?

 

Thanks for all the help I really appreciate it. Some synlube oil filter(I bought the truck not long ago and it doesnt need an oil change yet) and 10w30. The level is right, I guess i'm just worrying too much. thanks for the help though

 

The only thing I did't see already posted was the oil pressure sending unit. Possibly faulty.

 

Are the oil pressure sending units a commonly faulty problem? Mine worked fine till the intake manifold gaskets blew, after repairing the gaskets my oil pressure on start up is 40 then at operating temp it goes between 10-15, then sometimes when I stop at temp it drops to 0 and the check gauges light comes on. There is no pinging, knocking, or lifter tap at all, the engine purrs like brand new, so does that mean bad oil pressure sending unit??? I think it is, but i'm looking for that second opinion, thanks in advance!!

 

It is always possible that the sending unit is bad. The only true way to verify this is to remove the sending unit and install a mechanical gauge in its place for a true reading of the oil pressure. If all is well with a mechanical gauge, replace the sender.

 

Cool thanks again kyle, always there with best info. I am going to test it to make sure, but even still to replace the sending unit isn't that much, I think last I checked with autozone its only like 22bucks!! Thanks again!!