I just bought a 99 GMC SIERRA with a 4.3 v6 for $400 for a work pig, runs good, no noises, oil pressure at zero at idle, goes up to 25-30 psi when you give it some throttle, the oil looks clean and the P.O put marvel mystery oil in it, I was thinking about giving it a oil and filter change first to see what happens and check the oil pressure with a mechanical gauge, if I have to pull the oil pan Ill change the oil pump and maybe main bearings ? My question is does that sound like a good game plan, am I thinking about this correctly, any thoughts are greatly appreciated

 

It's a start. How many miles does you Chevy have on the odometer?

 

To tell you the truth I didn't pay any attention to that, Ill look in the morning, it was a mechanic friend's sons truck and he didn't feel like messing with it, so he offered it to me before scrapping it, it runs good, no noises

 

Back when I owned a Jeep CJ-5 I saw lots of them running low oil pressures, or at least at the gauge, but more like 10 PSI idle and 40 PSI max. the 258 C-I motor was like the Chevy 250. It just kept on running. Mine only ran between 30-40 PSI no matter what. Those old inline-sixes were short on HP, but great on torque and longevity, as long as you changed the oil and filter regularly. Jacked mine up 3" inches for the Rubicon Trail. With a granny 4-speed you could almost idle those old straight 6's over lots of solid granite rock in 4-low.

But back to your vehicle, if it really has no oil pressure showing, but still runs great, the old canard about fixing something that isn't broke comes into play here. As a side note, almost every semi-truck on the road these days is running a turbocharged inline-6 cylinder
diesel-powered 4-stoke engine. The inline 6 is inherently balanced and if a rig aint' running it's not making money. It's as simple as that..

 

Change the oil and filter but use a heavier oil.

 

Im going to check the pressure at the engine with a manual gauge and do exactly that

 

Its 194317