I fired my last 7.3 in -21 by cycling the glows twice and it fired and wasn't plugged in.
Last fall at elk camp it was 5 above, and Whitey barely started. Lottsa white smoke when it did... But there are only 2 glowplugs that work. Goes in Tuesday for new glow plugs and I'll replace the 6 year old batteries before it goes away from home this fall.
Old batteries and worn out glows are not helpful. Have the battery terminals cleaned really well or replaced too. Check the wiring also, it's likely old too. The best wire at a reasonable price I found was welding cable. Replace the wire between the batteries and to the starter. If you don't know, the older powerstrokes take a bit of oil out of the pan, put it under very high pressure and use that high pressure oil to fire the injectors. When dino oil gets that cold it's gets viscous and doesn't work well in that or any application.
I ran the Valvoline Extreme Blue full syn 5w40 all the time but I got it at a huge discount. You could easily just run it in the winter and go back to dino when it's warm. That said, that was my experience from 8-10 years ago, there may be other 5w40 full syn oils for diesel now, I sold the truck and have not kept up on the oils.
Micky
