There are some positive aspects of LPG power and the oil does stay clean or clear for a long time, same with the internal engine components, at least from what I can see of mine.
Mine uses an Impco model J vaporizer, not sure what carb is on it, and a 30 lb tank, like commonly seen on a forklift. Easy to change a tank out, but I pay way too much for refills, thats the only thing I'm not liking about it, $25 flat rate to refill, regardless if it's empty so if you want to top one off, it can be costly. My heating oil supplier just opened up a nice size LPG division, now time to see what my options are, thinking a few extra tanks will be it, right now it's $3.57/gallon at Agway, topped on off Sun. it worked out to $5.35 /gallon, might have to ask them about a gallon price, they probably won't do it though. When I first got this tractor, LPG was cheap, like $12 per 30 lb tank.
Cold weather starting can be an issue, and I do not know all the details, except the cold can keep the LPG from vaporizing, so if I leave it outside, I have to tarp it and use one of those LPG Ready Glo 44,000 btu heaters under it and a tarp, 15 min. of that and she will fire right up, then the coolant line from the engine, will supply heat to the vaporizer, just that initial start, though sometimes it has suprised me, 20 deg F it has started without heat.
The tractors with the mounted tank, seem to have some means to start on vapor and or you can fool with or adjust for cold weather starts, I don't know jack about those, that and the nurse tank and refill set up, kind wish I could refill my own, but maybe I'll find a better deal, the current one is a rip off.
PS, may sound odd, but this tractor has not had an oil change since Sept. '04, oil is clear, 15W- Rotella, though I'm not sure if that is pushing it, I will change it before winter and do so more often, at a glance, seems like those oil change intervals can definitely be extended, not sure what the norm is for LPG and what contaminants or breakdown of the oil occurs etc.