I was talking to a mechanic about motor oil, and he highly recommended Schaeffer's motor oil. I have a '92 Ford F-150 4x4 302cu. 5.0 engine with about 83,0000 miles on it. I guess Schaeffer's Supreme 7000 motor oil is synthetic-blend motor oil. He also recommended that I use SAE15W-40 weight motor oil. Reasoning was that 5W-30 or the 10W-30 is regulated by the goverment about how much additives goes into the motor oil and after 1994 it was required for warranty puposes. I guess the SAE15W-40 weight has more additives in it. Is this safe? Should I use the 15W-40 or stick with the 10W-30 weight motor oil? Have any of you guys used this particular brand of motor oil and what do you guys think of the product. I'm really concerned about putting straight synthetic motor oil in it, because of the 83,000 miles and all of the negative opinions I've been getting if I do use a straight synthectic motor oil. I'm currently using Valvoline 10W-30 Max-Life motor oil. Do these high-mileage motor oil benefit better than a synthetic or a synthetic-blend motor oil? Is Schaeffer's motor oil as good as Amsoil, Mobil 1 or any of the best motor oil out there?