I make the first runs of an engine on a test stand.

I use old fuel to break an engine in. I put a little castor oil in the old fuel.

If the engine quits because of old fuel, its no big deal, You are not flying the plane. Just keep the igniter on the glow plug.

I don't pay much attention to the Nitro. I don't buy anything beyond the 10% to 20% range anyway.