About 300 miles ago I put Motorcraft 5w20 in my 1995 Thunderbird, 4.6L V8 with 87,000 miles. I am thus far very pleased with the results. The engine is no noisier then it was with a 30 weight, and the car seems to have better response and is a bit quicker to rev. Gas mileage at this point seems excellent, but obviously I have not driven enough to determine if there are any real gains. I had previously tried a mix of Mobil 1 5w30 and 15w50 and the car did not seem to like that at all, it felt downright sluggish. Perhaps the modular V8s prefer a thinner oil.....