Unlike most petroleum based lubricants, unless there is a HUGE difference in tempuratures ( HIGH compression or HUSE PSI), 520 or 5-30 makes little difference. Because of the closer tolerances, and better lubricants out there today, viscosity amkes little if any difference the higher you go. Personally, if we can run 0 weight oils in our turbines here in Hawaii, and I run 0-30 MOBIL1 in my newer cars, the lighter the oil, the better the power output on a well sealed engine, as less is lost in friction and more heat is picked up in a faster moving, lower gravity lubricant.
Please,all you physics and chemistry bubba's chime in here. But if a gas turbine can run at 1200 degrees C and 40k rpm on light oil, and my Mustang and Suburban can as well in the humid, salty hot climate of Hawaii, it'll run anywhere ('cept Maybe Yuma)!
the people at ford said that if you don't put 5w20 in it will void the warranty stupid people. i swear. i haven't really tried different stuff cause i'm gettin work done under warranty and really don't wanna void it right now. personally i would run 5w20 sythetic but i guess that's just me. and it's made...just extremely hard to find..noone carries it. well that's my 2 cents
I belive that they started saying 5w20 on the 2001 models, cuz my friends 2000 GT calls for 5w30, who knows what they are thinking. I just run the Motorcraft 5W20 synthetic blend. I think it would be a little hard for the dealership to know if you were running 5w20 or 5w30, if they ask just tell them that you use 5w20 and you shouldn't have any problems....Unless they give you a polygraph test.