I have a new "USED" 1996 Buick Park Avenue with 147,000 mile on it. I've run Valvoline synthetic in my other 1993 PA Ultra and my wife's Chevrolet Lumina (1993). Usually 10-30 in the summer. However, I noticed that the oil pressure was around 30 PSI on this car with the new oil change. So... I changed it again with about 200 miles on it and put in 1 qt of 20-40 Valvoline Synthetic and the rest 10-30 Valvoline Synthetic. Now the pressure is around 45-50 lbs. It comes up to pressure very fast after starting and continues to hold pressure very well. Has anyone ever heard of this causing problems? I am really considering getting some 10-40 Amsoil from my neighbor up the road. Also, (and this may be a Buick PA issue) my light comes on saying "check oil level". I do and it completetly full, CLEAN, but full Any idea why that might happen?