Oil pressure and mult-viscosity oil.

Posted by Rscott77x on 2019/11/9 20:25:36
I started using Rotilla T4 in my 1947 Clipper's 356 cu inch engine. A well know Packard specialist informed me he was using in one of his Packards and it helped quiet down the engine. As my car has some noisy lifters I started using it as well. It did have a significant effect in quieting down the engine.
Around town, the engine has always consistently shown about 40 lbs of oil pressure .
Recently, I had some work done on the car which included having the OD repaired. I drove home, about 1 1/2 hour drive, and was able to easily travel at 65 MPH with the OD engaged. As I got close to home, I noticed the oil pressure had dropped to 20 lbs...I do not know when this started during the drive as I was watching traffic.
A few days later, I drove the car around town and (45-50 mph) and the oil pressure was at the usual 40 lbs.
When I start the car, the oil pressure briefly spikes to 50 which is caused, I think, by the effort of filling the oil filter canister.
My question is would the OD lower the engine RPM so much that the oil pressure would drop to 20 lbs? Or does the 15w-40 oil have some effect here.
As the oil heats up, it becomes 40w...thicker!! That should increase oil pressure, if at all.

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