The last diesel I drove on a regular basis was a metallic green 1982 VW rabbit diesel with British tan interior that I drove mostly in mid-late 80s. It was "Fully Loaded", which back then basically just meant that it had a/c and an AM/FM stereo. IIRC it had about 52 horsepower and 89 ft of torque. The top fuel economy I recorded was 52.4 mpg on a 400 mile trip through western NY and northern PA in the fall. Temperature was in the 50s, high pressure, dry, windows up, no a/c. The mpg commonly flirted with 50 on the highway and was in the high 30s/low40s around town.
My "winter driving kit" included a block heater, a propane torch, an extra battery w/ cables, anti-gel, and the oxy-acetylene kit in my garage at the time (more on that last one later). See, we had some crazy cold winters back then, with temperatures under -10 F and even a few down to -25F. I haven't seen temperatures like that since, well probably the early 90s.
If you have cold winters, the first thing to keep in mind is that you better change your fuel filter by Thanksgiving, because the things will gel up and any little bit of dirt or moisture will make it worse. You wanted to have a clean filter. Had to put that anti-gel in the tank, too. However, when those temperatures dropped to -10 or -15 or colder, and you weren't able to plug in the block heater, then the car sometimes would turn-over but never start. You can only run the glow plugs so long and if that fails then you need to go to phase II, because most likely your fuel is gelled anyway.
Phase II means pulling out the propane torch and gently heating up the canister where the fuel filter is (avoid the fuel lines!). This warms up the fuel and gets it flowing again (and it warms up your hands!). Keep a fire extinguisher handy and keep your engine compartment clean.
Of course, it's not uncommon for your battery to run low during one of these 20-minute engine starting exercises, in which case you pull out battery #2, and.....here's the trick: You hook the batteries up in series to create 24V. Now, you don't want to hit the glow plugs for very long at 24V so you have to quickly turn the key and turn over the car. Boy do those dash lights light up! (probably couldn't do that with computers these days, I'm thinking?) The engine really turns over and as long as you've got fuel flowing, usually it will start at that point.
I kept the car in an unheated garage then and one time I forgot to plug it in and couldn't get it started, it was -18. Fortunately, I remembered to bring my extra battery into the house to keep it warm and trickle charged by the boot rack, so I swapped out a warm battery from the house, heated up the fuel filter but it wouldn't quite catch. One of the glow plugs was out, it seemed. So, in a "Now what?" moment I grabbed the oxy-acetylene torch, drilled a small hole in in the air filter cover, turned on the oxygen (no acetylene! It's unstable under pressure and will detonate!) , and shoved the hose in the air intake. Bam! if that thing didn't start right up!. So, I put some electrical tape over the hole and left it there in case I ever had to use it again. In fact most of the times after that I just did it as a demonstration for friends on how the oxygen could start the car, even without glow plugs.
Now, a few months after I started demonstrating the oxygen thing, the car did blow a ring at 220,000 miles. Hard to say if it was my oxygen trick or the 220,000 miles. Given the engine displacement and the oxygen rate I was probably only enriching the oxygen content by 5 or 10%, but that sure was enough. So, anyway I put all new rings in it and it ran great for two more winters, extra batteries and all, until it hit a deer at 262,000 miles and went to the great recycling yard beyond.