On my 2nd 1987 IROC LB-9 (High Mileage)... I have noticed that my Oil pressure readings are good until I have driven it over 30 miles and/or 40 minutes...

About 6 months ago I had oil pressure issues and found out that my oil pump was failing...thus I had a new hi-volume OP installed as well as new crank shaft and rod bearings.. (this was more of band-aid fix to give me some time before rebuilding the entire engine). IROC runs great, good idle, no hesitation, no overheating, idles at 550 in "D". I am running Castrol GTX 10w-40 with a Fram PH-30.

*When driving at speed OP sits at a good 45-50 psi
*when around town in "D" OP sits at a good 30 psi
-- WHEN I DRIVE IT MORE THAN 40 MINUTES or over 30 miles at HWY speeds In Park OP is 27 psi and in "Drive" it sits on first tick mark above red and sometimes even right above the red.

QUESTION:??? Could the oil be thinning out that dramatically when car is driven over 40 minutes? Both Fans are config with a switch so the car is never overheating and temps sit at 180 all the time. Aside from the crankshaft and rod bearings... would the worn cam shaft bearings??? really make that much difference?? Anything else I am missing along the oil passage path that I may be missing that would be worn and accounting for the falling OIL pressure in this weird sense...??? I have tried 20w-50 and it seems to help a little so might have to go with that.... OR with a straight 30 wt?

QUESTION:

I wouldn't worry about it too much, if memory serves me idle oil pressure should be atleast 8 psi @ 500 rpm. Running mobil 1 10w40 my Vette idles with 10 psi when it is warmed up. The 20k mile 350 in my Express does not carry much idle oil pressure either.

I would NEVER RUN A FRAM FILTER on anything I cared about.

use wix filters....only! you can try Castrol HD 40 oil .it will push the oil pressure up nicely.

I use mobil 1 filters, not Wix.....I like the look and quality of the materials in the mobil filters better