18 month old gas is not ideal, but I'd be curious how you know it's
degraded? Draining the old gas should work by using a syphone hose and
jerry can. Some recylers w/ take it if it's labled.
If you add a gasoline a good gasoline additive to the new gas and
changed over to a good synthetic lube, you s/b good 2-go.
RH

Depends how it was stored. If it was indoors it should be fine, though
it'll stink when you get it running until you get fresh gas in it. Some
of the thinner solvents will be gone from evaporation in the gas no
matter how well it's been stored. Wisconsin winter gas (I'm in Fort
Atkinson) would have had more of the thin stuff to evaporate since it's
designed to be stored & used in cold temperatures. Summer gas has less
solvents in it to make it less evaporative in summer heat. The old gas
won't stop you from getting the van running all other things being the
same, but it might make it harder to start or keep running decently if
it's really marginal in the ignition or fuel delivery departments.

I'd throw in some injector cleaner to add some more thinning solvents to
the old gas, and a can of HEET to get rid if some of the water that's
probably condensed in the tank & fuel lines. Get a new fuel filter right
off the bat too. If the ignition system is OK, that should be fine. Then
make sure you use up that gas asap, and expect it to smell funny, get
terrible mileage and run kinda crappy until you get something in there
less than 18+ months old. ;)

Obviously, you're going to want to change the oil & filter as soon as
you get it running since there's likely to be a bunch of water in the
crankcase from condensation as well. The antifreeze should be OK for
now, but maybe not for when it actually gets to below freezing around here.

Cheers,
 - JJ

I had a 1987 Nissan Stanza sit for 3 years with a nearly full tank of gas
...started it up, passed DEQ...no problems with the "old gas' whatsoever. I
had a 1989 Dodge van sit for nearly two years, same result...with a 33 gal
tank I had no interest in dumping the gas unless I had to. Now with my lawn
mower or weed-whacker, if left sitting over the winter I happily dump the
gas....Rod