CAUSES? High oil pressure

"HI MILEAGE" motor oil isn't any thicker. It just has additives in it for use in engine that are a litlle more worn. A 20w50 motor oil is a 20w50 motor oil no matter if it's hi mileage or not. It's a viscosity rating(20w50, 10w30 etc) so it has to be the same as ony other oil rated the same weight.

Personally I don't necessarily think the high mileage oils are anything but hype & that you are either going to just leak or burn more expensive oil than you would with regular oil. But that's JMO.

I think the 1st thing you have to do is verify what the oil pressure really is. Secondly what do you define as high?