Great read about oil wieghts.

http://www.synlube.com/sae5w-20.htm

 

I have been using only 20-50 weight oil in all seasons and climates for over 30 years, even winter...also have used it used in racing engines. Changed oilevery 3000-3500 miles faithfully....or after each race.My 1989 Montero has passed 200,000 miles; never any lubrication problem or failures in engine since it was new and no leaks....quiet and great compression! I figure that oil is a lot cheaper than steel...even these days!! Good luck with your Mit!

 

Interesting reading. My 02 MustangGT requires 5W-20W oil. We have decussed this on our Stang board many of times. Must of us use 5-20 as stated by Ford. The 4.6V8 engine is considered a "close tolerance" engine like many today. According to Ford, we must use 5-20 to adequately libricate the engine. To me, it comes down to changing oil on a regular basis and proper maintenance of the vehicle. Pearl02