You're using 10-40 in a track pack GT or regular GT? Do you live in a warm climate? How long have you been using 10-40 for? Where you burning lower weight oil?
Climate is Socal. Although I do take the car to the mountains in the winter to snowboard - temps can drop to 20 F or so.
So would you recommend using the 5w50 or 10w40?
I use synthetic 10W40 in my GT track pack. Used for about a year. Only had the car a year, never burns oil. its not my DD. i primarily use it in the non winter months for Autocross. So cold weather starts are infrequent (never below freezing). hence why I suggested that the winter component (10W or 20W) for me doesn't matter ,and in your climate, might not matter. 20F isnt really that cold either, espically if was only for infrequent snow board trips.
I would not recommend going with 20W50. Ford recommends 5W20 for standard coyotes and 5W50 for the track package. Using a W20 to W50 might be OK, but using a 10W and 20W might be asking for trouble and depends on the climate.
Here is something worth reading. https://www.allfordmustangs.com/forum...-5w50-oil.html
I agree depends on climate, I said that when i noted that the OP was in warm Los Angeles..
this list, which you quoted is what i based my choice on. (ignore the Amsoil and pick your favourite brand)
"Amsoil ALM 5W-20 – If your car is 100% stock, never raced, driven like a grandma, or short trip driven, no matter the climate….use this. *Mustang GT only*
Amsoil AZO 0W-30 - If your car is driven year round up north in very cold temperatures with bolt on mods, street/drag raced during the summer, and you want one oil for year round use....use this.
Amsoil ATM 10W-30 - If your car is moderate to heavily modded, used in hotter climate states, or never driven during winter months in northern states...use this. *If you always short trip the car, use Amsoil AZO or ALM instead (never get the oil up to full temperature)*
Amsoil RD30 10W-30 - If your street car is modded to the max and producing HP beyond 600 rwhp, turbo or Supercharged, especially E85 fuel engines...use this.
Amsoil XLO 10W-40 - If you have a Boss 302 or Track Pack GT, and you close course run your car for the experience (learning - short heats)....use this.
Amsoil Dominator 15W-50 - If you have a Boss 302 or Track Pack GT, and you close course race your car in competition for extended sessions….use this. This lubricant is best suited when pushing your car to the edge of cooling limits from sustained high rpm operation. *Not optimal for short trip, grocery getting street duties*
*Boss 302 and Track Pack GT owners - If you do not road race your car, use Amsoil ATM 10W-30. 5W-50 spec for this engine is overkill and results in excessive oil pressure.*"