I have an oil temp gauge in my truck and the scale starts at 140. I took my truck out today for about 20 miles (it was about 40 out today) and the oil didn't even get up to the 140 mark.

I read in hot rod one time that optimum oil temp was over 200.
what gives?
I have 10W-30 in the thing, maybe I should put lighter oil in considering how cold the oil stays.