The factory recommended engine oil viscosity is 10w-30 for the SRT-10. 0w-20 is a full viscosity grade lower (thinner). If youre concerned about cold weather performance, try 5w-30.
All of the above are bad suggestions.
Factory fill is Mobil1 0W40 Great for cold weather start ups (0W) and more than enough protection without parasitic losses at full engine temperatures even out here in Arizona.
Cheers!
Hmmm, 132,800 miles says I am correct with 15-50.