Q: My next-door neighbor tells me I should add a quart of automatic transmission fluid to my 2002 Corvette's gas tank before I put it away for the winter. He says this will keep the gas from gelling. Is this another old wives' tale?
A: I think he's confusing a couple of good ideas from older times. It used to be common to add a small amount of oil, often marketed as "top oil," to fuel tanks to provide extra lubrication for the valvetrain. But this became less and less necessary starting as long ago as the '60s, back when valve guides were simple holes drilled into an iron cylinder head. Lately, the guides--bronze sleeves pressed into the head casting--are more wear-resistant. When we transitioned to unleaded fuel, there were major concerns with valve-seat recession caused by the lack of lubricating lead compounds in the fuel.
Additives to fix this problem are still on the shelves. (See the letter below.) And it's a common practice to add antigelling additives to diesel vehicles to keep the fuel from turning into big, waxy flakes in the tank in cold weather. None of this stuff applies to your relatively new Corvette. Moreover, adding ATF to your tank is likely to contaminate the oxygen sensors with zinc or phosphorus compounds. These are extreme-pressure additives, necessary because the transmission has plenty of steel gear teeth sliding over one another--not really a concern in the engine. So save the ATF for the transmission.
Q: I have a 1966 T-Bird with the 390 engine. Do I need to use a lead additive in the fuel?
A: Technically, yes. From the top: Tetraethyl lead was used in gasoline from the mid-1920s until the mid-1980s. It boosted the octane rating of gasoline substantially and very inexpensively. That permitted the petroleum companies to utilize more of the low-octane fractions in a barrel of crude--that's part of the reason gasoline was so inexpensive in this country for so many generations. As compression ratios and overall efficiency rose, cars required higher and higher octane, so the refineries had to process the crude oil more to raise the octane of the poorer fractions high enough to prevent knocking. That takes time and money. There was an unexpected side benefit to adding this lead compound to the fuel: As the gasoline burned off, it left a small amount of metallic lead film plating everything in the combustion chamber. That thin film acted as a lubricant and antierosion agent at the interface between the red-hot exhaust valve and its cast-iron seat.
Suddenly it's the '70s, and we recognize lead as an environmental toxin. It also contaminates catalytic converters almost instantly. Federal regulations start to ban lead from gasoline. The car companies combat increased valve-seat recession by using better metallurgy in the valves and by sinking hardened metal valve-seat inserts into the heads instead of just machining the raw cast iron.
Problem: The owners of older cars like yours are stuck. You can get non-lead-based additives intended to prevent valve recession, but I'm not convinced they're really that effective. If your T-Bird is a pampered toy and not a daily driver (and I'm guessing it is), the modest amount of light-duty driving you give it probably won't wear out the valve seats very fast. Just enjoy it, and when the compression goes down, pull the heads off and get the valves done. It's not very expensive to replace the exhaust valves with upgraded ones and get the seats machined for hardened, unleaded fuel-rated inserts.