Which type of oil to use

I live in northern Colorado. My 273 is stock and 160,000 miles on its last rebuild.

our temps run 0F to 100F.

I use 10W40 (would prefer to have 5W40 as the 0-32F range the oil pours like molasses)

On a new rebuild I would use 5W30 or 10W30

Many newer cars use 5W20 (better clearances)

The FSM calls for 30W for most regions MyMopar.com free FSM download for your car or for your engines year