My dad has a1996 5.9 with around 300k on it idlin it only has 20lbs oil pressure my 97 has 200k on it and it has 40psi idlin I was wondering where would the best place to start improving it. I work on large engines for a living and rods and mains are the normal culprits but I was wondering what was normal for these smaller engines thx in advance

 

Mine with 300 is around 30 once warmed up @ idle then increase as I drive I run dello for oil in mine as that is what I was using in my semi's hope that helps

 

Lower end bearings wearing out will cause low oil pressure. 300k seems kinda soon tho

 

Try 15w50 diesel oil instead of 40w
Mystik JT-8 sold at most farm stores and auto parts places.
25-30 dollars sold in 2 gallon jugs.
It is semi-synthetic.

 

I don't trust the gauge in the dash, in my 96 mine would say 20 psi going 65 mph on the highway sometimes. Installed a mechanical gauge to the port on top of the filter and have 32 psi at idle when warm and between 60-70 on the highway.

 

I Agee stock gauge is more like an idiot light not very accruate insatall aftermarket gauge

 

Never install the gauge by the filter... You need to install it in the main galley, that is where the stock sending unit is.. If you have to tee to keep the stock gauges then tee it. I had 546000 miles when I got my 94 the idle was about 550-600 and the oil light would come on when warm at idle. I raised the idle to 700, the light flickered when warm. I didnt drive it due to it being an ugly, greasy beast. I bought it for the engine!! When I installed the 12v into my 3rd gen 1500 I put a mechanical gauge on and oil pressure never fell below 26 psi. The stock sending units wear out, gauge is usually good, broke completly or bad ground... If it has a bad ground your volt meter would move with your turn signal flashes!! I would check with mechanical gauge warm and replace the sending unit if reading is different at my shop...

 

I agree that in the gallery is the best place for it but the easiest way for a quick check is at the filter housing and it will still give you a better idea of what is going on then the factory gauge. I know lots of people who have their gauge installed in the port above the oil filter and no ones has problems. From a technical stand point I should see pressure on my mechanical gauge before I ever see pressure on my factory gauge because oil will pressurize first through the filter before it gets to the factory gauge, but I don't my factory gauge almost instantly jumps up to 40 psi and it takes quite a bit more time before I see anything on my mech. gauge.

 

If you have low oil pressure once the truck is at operating temperature switch to Mystik JT-8 15w50
That will bump up your oil pressure at least 10 PSI.