Diesel Engine oil..Preference?

[John SD]

Been using 5W40 synthetic in diesels that must run in winter. Kubota starts good in unheated shed without being plugged in down to 0. Last year I used Rotella synthetic. This year the oil is changed with Cenex Maxtron 5W40.

10w OR 15w is too thick for SD winters, or is it just that you don't plug in?

I do plug it in if temps are teens or lower, but sometimes I take the tractor out on unanticipated runs on short notice I should mention the Kubota has glow plugs, but they only come on if the temp is at a certain temperature or lower.

IMO, 15W anything is too thick for SD winters. Coolant heaters alone don't do a lot for oil in the pan.

In the past I have also used regular 10W30 oil. Honestly don't notice much difference in cold starting on 10W30 vs 5W40.

My old Ford starters are borderline for cold weather no matter what oil I use. The Fords get plugged in for a while anytime below freezing. 24/7 if it's below 0.