He didn’t expect to break an axle. Took what weapons he could, torched the rest with the disabled truck. Guns n ammo is heavy stuff.
Why did he set fire to the truck? As I understand, it was on some forestry road; those are 1-lane (at best) and nobody drives there without need. He could have left the truck without burning it, and then nobody would know that it's his truck - not for days, if not for weeks.
Why would he set up a base on a mountain, in a place where strangers stand out and where you have only a few easily blockable roads? A place that requires either assistance or frequent trips to cities to obtain food. A place where he is not a typical person around. That would make no sense.
It does sound, though, improbable that he intentionally drove his truck up there, intentionally left some of his stuff, intentionally broke the axle (how do you do that on demand?) and then disappeared into nowhere. Most of this stuff doesn't help him at all. I must surmise it was an accident, and his plan B failed just like the plan A. Now he is on plan C, hoofing it through a foot of snow on terrain that is inhospitable even in a warmer season. The Occam's Razor tells me that Mr. Dorner is not as smart as he claimed; he is probably laying dead in some ravine, with broken neck from a fall. His tracks and his body are covered with fresh snow, and by spring there will be nothing left to recover. Coyotes will tear his skeleton apart and carry each bone far away; the buzzards will do the same with whatever they can lift. The animals are probably already busy. He may never be found.