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.
