I have block heaters on our gas vehicles. Don't use them much, even in subzero weather. Probably should.
Our new Volvos with Cummins at work are embarrassing to the Cummins name. Between all the computerized crap and the evil "regen" smog systems, they are absolutely MISERABLE trucks to have in cold weather. They are costing the company a bloody fortune in frozen trucks and breakdowns and repairs and wasted fuel.
You cannot simply leave them running when it gets brutally cold. The smog system will plug while idling for even just a couple hours, much less extended periods. When that happens, it will quickly progress to an expensive breakdown since the truck cannot regen itself while idling. So it shuts down and freezes up anyway.
If you drive all the way to work over the weekend to "regen" the truck manually, which I sure as hell won't do, you will have to sit and wait for one to two hours for it to maybe; hopefully; get hot enough (1200 degrees) to get the job done. You must then reset the fast idle to keep the truck running again, else it will shut itself off and freeze solid.
The fuel filters, exposed, uninsulated, and too far from the motor to get any engine heat, have silly little 12v electric heater coils that do not work well and do no good at all if the fuel in the tanks and lines is gelling. Headquarters for our company is in Tennessee where they have NO CONCEPT of what sustained sub-zero weather is, so the morons refuse to pay a little extra to have in-tank heaters installed or ordered on our new trucks. They are VERY effective and simply reroute hot engine coolant through a series of coils in each tank to warm the fuel while the engine is running.
Ever since ULSD came out, I swear the cold weather properties of diesel have taken a downward plunge. You need so much and so many additives, it is very expensive. And they only do a marginal job.
The company is doing all it can to make the freezing and gelling and dead-truck issue the "driver's problem". They dictate using their fuel at the terminal and insist it is properly treated and "DO NOT ADD any Additives!!". So we do as told, and ALL of our trucks gelled up. Now it is "You MUST Add this stuff and this amount", except they run out of it and many trucks are still gelling.
If your truck is not left running all week and weekend and won't start, it is YOUR fault. If you leave it run and it clogs the regen system (guaranteed it will), that is also YOUR fault. The extra fuel consumed will also be held against your fuel mileage bonus, so forget getting any bonus. These computerized smog Cummins get such lousy mileage anyway that fuel bonuses are a thing of the past to begin with.
I told the new shop manager, in charge of all this stuff, that I was going home for the weekend and I had filled my tanks with HIS fuel, HIS additive package, and plugged it in. He wanted it left running. "OK, but I will not be driving the 30 mile round trip every 10 to 12 hours to manually regen the thing. I have things to do of my own and I don't get compensated for the time or fuel to do that. "
"Well, it will be your fault if it clogs up. "
"No. It won't. But, then I will plug it in. If it won't start Sunday night, I will go home and your truck and loads can sit until warmer weather for all I care. It is the company's truck. I did NOT spec it. I did NOT choose the fuel or additives. I damned sure did NOT design such a miserable smog system. Have a nice weekend. "
Any diesel truck with properly treated fuel and good batteries that will not start when left plugged in is not worth owning. Especially now that the Government has decided the air coming out the stack must be cleaner than the air going into the intake filter. You could not GIVE me a new personal truck with those nightmarishly expensive and unreliable systems.
Attention: TDR Forum Junkies 
, thought I be able to give it a try when I was in KC for Thanksgiving but it only got down it the high twenties which has been our lows down here lately:{ (Having an Open Air Produce Stand cold weather doesn't help sales). 
but I was dressed 
for cold weather).
