I'm running 20w50 in both my '95 Dakota and my '81 D-250. The Dakota pops right off with no problems, its nearing 200k however and its a loose motor. The motor in the D-250 only has 28k on it so I'm considering switching back to 10w40.

I've had to drop oil in it in the mid 20s and yeah that 20w50 was pretty danged thick. Came out like goo out of the cold bottle. It also takes some time when its cold out to get the lifters pumped up.

I fired it off last week in mid-teens weather and it did okay once the oil got to pumping (took a few secs though). It did crank slowly though.