1. Air leaks in the fuel system. If any of the negative pressure components have an air leak you'll be sucking air. This means less fuel, but more crucially less lubrication. High pressure injection pumps are meant to be lubricated by fuel.

2. Algae. Sometimes a fuel system can be contaminated by extremophiles that grow in untreated fuel. This will merely clog filters, and in the absence of water or air leaks will cause only fuel starvation and no engine damage.

3. Water. Water will turn into a steam bubble in the vacuum of the suction stroke of the injector pump, and then on the subsequent compression stroke the bubble will cavitate--turn inside out--and blast the wall of the injection pump cylinder with an extremely concentrated high temperature jet. Doing this hundreds of times per second wreaks havoc on the poor engine.

So if your fuel is dry and clean you're good.

For the pollution question, my retort is "which kind?" I claim diesels create more NOx and soot for less CO2. So, which is your priority?

I'd say "it depends". In a dense city I see NOx and soot as being a higher priority. If you're out in the sticks, probably your contribution to global warming (CO2 et al) should be weighted more heavily.

> "Google disagrees with the comment about diesel fuel. It looks like 6-12 months"

> I don't know where Google is getting their information from, but I've personally started diesels I know haven't run in 20+yr on the first crank.

> So if your fuel is dry and clean you're good.

They are talking about diesel fuel, which definitely has a shelf life without additives to keep it from turning to mush.

Its definitely much shorter than a decade, but if stored really well more than a year is pretty doable. 2+ years can be a gamble though. And if it causes problems, it might cause some serious problems. Want to gamble on your generator during an emergency?

I've definitely had some gas sitting in a tank with stabilizer last a couple of years. I've definitely had gas sitting in a tank go bad in under a year.