Thanks for all the good advice - I always like listening and learning.
Been trying to hunt that one down since I got this truck ten years ago.
I had even higher engine temps before I replaced my radiator to a 3 core two years ago and don't use water/coolant any more.
I still have an original 30psi gauge, which is pegged at warmup and during in-town driving.
In the summer it goes down to 20 or lower at idle, in town and short trips. Longer trips and standing in traffic drops the pressure to almost 0.
On the freeway at 2500-3000 rpm the pressure drops eventually to 20 after a while and almost to 0 pressure at idle, coming off the freeway.
The hot summers make the pressure drop faster and keep it down.
The oil gauge seems to read very accurately; replaced the oil gauge line; bypass filter is correct type and installed properly with the proper sized lines.
Head gets the right amount of oil. Timing is lean and beautiful (tried all kinds of retarded and advanced settings over the years). Distributer works beautiful and is even.
Rebuilt the head completely last year.
No smoke or burning oil excessively.
Nice pressure in all cylinders - about 125.
The block just can't hold the pressure any more once everything gets hot.
Since everything else on the engine sounds and works beautifully, I always asumed the bearings must be too worn and allowing pressure to bleed off.
