20w 50 oil is used in diesel engines and v-twin motorcycle engines.. so i guess if you live some where its hot enough that the heavier oil can heat up quickly then go for it. the oil needs to heat up fast so that it flows good enough to prevent cold start engine wear.
If you are using it to try to slow a rear main seal leak then i wouldnt recomend it because all your gonna do it create a sludge ball in your engine.
if you are using it because you live in death valley and/or Baja race then yes use the 20w-50