I bought a 98 f150 with the 4.6 V8. When I bought the truck it had castrol GTX 5w30 and a hastings/baldwin filter on it. Not a bad choice. And the guy had a bunch of receipts for 4k oil changes. The truck has 35k miles on it now. I changed right over to mobil 1 5w30 for the summer with motorcraft filters. The mobil1 is at about 2200 miles in the engine. It consumed about a half a quart in these 2200 miles, and the oil is very dark looking. The inside of the valve cover looks amazing, zero varnish. So is the mobil1 just cleaning up the system really well and consuming a bit? Its not leaking a drop anywhere, and the motor runs like a top. I am thinking of going to german castrol 0w30 next oil change if i can get my paws on some. Any thoughts/recommendations?