I see Tier 4 has now entered this thread. For the record, it was -31ー here this morning. High this afternoon actually did reach +10ー. My nephew and I spent the day moving bales, feeding cattle, and loading out 2 trucks of grain. We both have Tier 4 Kubotas. They are the only tractors that would start today. We go by the book - Kubota says #1 diesel for temperatures 14ーF or colder so we run #1 all winter. We never use a blend because colder than about -10ー and you'll have problems. My nephew doesn't use any additives. I use Shaeffer's 2000. So from we who live colder than 0ーF from December through February its #1 diesel. Yes, running #1 means worse fuel economy but the cattle need to be fed. Additives - may help if you have #2 in the tank and you need to run when it gets cold but our supplier starts giving us #1 in November and we run that until March. Turning the engine over to get it running is often a problem when the temps are colder than -30ーF. Block heater is enough from 0ー and colder.