UPS in Sacramento switched the delivery rigs to Diesel several years ago. They let the old gasoline tank sit for over a year before offering the left over gas for free to employees. Those that had low fuel tanks at the time had total engine damage, valves stuck in the heads letting the pistons hit open valves. Total overhauls needed. Many had less than empty tanks and maybe got 1/4 tank of free gas. Those engines lived but ran like crap till it was burned up and new fuel installed.
Talk with any machine shop about old gas damage and you will hear true horror stories, same for Lawn mower shops, most have signs warning you not to run old gas in engines.
When an engine runs on old gas it does not burn well, there is a residue like shellac that forms on the piston heads and on the valves. It is actually pretty on the pistons but is shiny goo that is hard to remove if you are trying to save the pistons. It also leave a god awful smell in the engine that will have the entire machine shop stinking after the engine is torn down. Anyone that has been around one of these bad gas engines knows the smell. It is not horrible but very distinct and you don't forget it.
I only share this hoping you guys can avoid similar fate. $50 worth of gas is not worth destroying a $7500 engine, or if you count labor make that number $15,000.
I repaired a boat for a friend 3 years ago, lucky for her 6 of 8 injectors plugged when they first launched the boat after sitting for over 4 years. The boat held 65 gallons of gas, it had around 20 gallons in it of bad gas. A potential buyer of this boat added 20 gallons of fresh gas "to be safe" before his test drive of this boat before buying it. My friend was a recent widow and was selling off her husbands toys. Someone she knew wanted to buy the boat and she let them take if for a test drive after putting in a new battery. It never ran long enough to move much past the dock. Plugged 6 injectors on a 8.2l GM big block which killed the engine and saved it from Piston and valve damage.
I flushed all 8 injectors, washed a gold goo like gel out of them and got them spraying a good pattern again. Flushed the huge gas tank and lines, and had the engine purring again. Bad gas does bad things. The boat was a nice 27 foot Cobalt so it was definitely worth repairing. Sold for $24,500. On the good running test drive it pushed nearly 63 MPH. Engine ran great.
I would never use old gas in a small engine; there's just not enough dilution to make it safe for the engine. I run ethanol-free with stabilizer year 'round in my small engines (mower, snowblower). I've seen and fixed many a mower carburetor that's been plugged due to old gas. If I put it in the car's tank I'd dilute it well and use it up a little at a time.