Before even thinking of cranking that engine I would pull all the plugs and install come Marvin's Mystery oil and a fuel system cleaner like BG-44K of Berryman's Chemtool-12 into each cylinder to let them soak the pistons and rings a while.

Earlier this week I read of some recipe for 1/3 Marvin's and 1/3 each of two other ingredients, but I can't remember them. ATF might have been the third item.

Then put a breaker bar and socket (27mm?) on the crank bolt and gently rock the crank both directions to allow the chemicals to loosen any corrosion inside the cylinders.

I'd then run the old gas through (or siphon it out if I could do so safely & start with fresh gas) along with the BG 44K.

Then change the fuel filter and oil & filter.

I've seen it on Volvo tanks (especially plastic ones in the 700) and on other auto tanks. But especially in marine fuel systems when winterization isn't done. One winter is enough to varnish carbs and throttle bodies.

I posted about horrendously varnished 740 tanks before, and got some comical email from people who practically called me stupid for even mentioning it. But no matter. I wish those who laughed a tank full of varnish and a glued set of valves. Because that's what a good quantity of ingested varnish will cause.

You might or might not find varnish in the fuel tank. Cleaning it out would not hurt; that much I assure you. It isn't that hard to drop the tank, and there is certain to have been some sort of degradation. Fortunatly you've skirted the reformulated fuel problems which account for much, if not most varnishing.

Personally I'd say, if you're serious about a restoration, this project will prove to be only a slight bump in the road. And you might discover a lot of debris in there anyway. Either way, I'd NEVER run a 15 year old supply of gas. But that's just my (professional) opinion.
--
1992 940 wagon, 72k
make people envious; smile often.