I have a '93 Buick LeSabre I bought about three months ago. It now has about 25,000 original miles and I've made it a habit to observe the gauges so I would know what 'normal' position is. Since I bought it the oil pressure has been just above 70 when driving. This weekend I had the oil changed and switched to Mobil 1. The gauge now reads 80 when I drive. I checked the dipstick and it's a little above the "FULL" line but not by much. Could changing to a synthetic oil cause a higher oil pressure reading? Could slightly overfilling cause it? Thanks very much.