TL/DR: Can’t understand why my engine is running oil pressure so much higher than expected.
Background - I bought this car in 2019 at 94,000 miles. The story (and mods) is documented at My ‘new’ ‘70 Cougar! Where to begin??. FF to today, I have driven 14,000 miles of near perfect performance! My only issue ihas been that the previous owner’s builder used Crane plastic guide plate bushings (which failed after 10,000 miles). Fortunately caught the ticking before it damaged the lifters, cam or pushrod. Last year the heads were machined for proper steel guide plates and 7/16 rocker studs. Now, the car runs and drives like a champ again - routinely eating up 200+ miles of odometer a few times a month.
The only issue I struggle with is the fine mist of 10W-30 VR-1 that is seen streamed across my FL1A filter, that I change every six months/1500 miles. There’s also a drop at the base of the fuel pump. I assume this is only happening during driving because there’s never more than a drop or two on the garage floor when parked. I can’t find the leak. I’ve spent hours looking and even reset the intake and valve cover gaskets.
This all came to my attention when installing a Shelby-style gauge pod with matched gauges/sending units. I operate both (aftermarket oil psi and Motorcraft SW1311 dummy light) senders threaded it onto a brass adapter, which is then threaded to the port on top of the block. I about flipped when the needle was pegged at 80+ psi! First, I blamed the sender, then the wiring, then the ground, and finally the gauge itself. I wouldn’t expect the brass adapter to contribute to the gauge falsely reading high.
So I sprung for a mechanical gauge and threaded it to the T adapter - in place of the dummy light sender. Much to my surprise, it read 85 psi at start up! As the engine warmed up, it gradually dropped to 67 psi @ 1000 RPMs. I put a multimeter to the aftermarket sender wire, which read 73Ω to ground. That matched to about 67 psi. When I took it to 2000 RPMs, it ran up to 78 psi. At 2500 RPM, the mechanical gauge was at 81 psi!!
So now, I actually believe my engine runs at a ridiculously high oil pressure. Could normal driving RPMs at these high pressures and wind be forcing small amounts of oil to “leak” is causing the dispersion on my oil filter, with no garage floor drips.
So…my original question: What might cause my 351 Cleveland to run at oil pressures from 67 psi (warm/idle) to 81 psi (warm/2500 RPM)? Maybe a stuck by-pass valve? I can see a rebuilder choosing a higher volume oil pump, but most of those are standard pressure, anyway. Can I continue to run it without harming my engine? If not, how far after 14K miles would it become a problem?