Bobby , the original handbook that came with my truck says to use 20W or SAE 20 down to 32 deg F .
20w as low as +10F
10W as low as - 10F
10W + 10% Kerosine below -10F
It also says to drain the crankcase every 2000 - 3000 miles or more often in dirty conditions .
During new engine break in , the book says to use 10W for the first 1000 miles ( with a hot drain at 500 miles ).
'40 Chev 1/2 ton - 216
