The Old Gray Grit Ain’t What It Used to Be

A car collector put his Packard away for about 30 years. When he took the car out of storage, there was no getting it started. “Why, this car used to be a ‘gas’ when I drove it,” he said. He couldn’t understand why it didn’t run now. The reason? His gas used to be a “gas” too — now it’s just a gritty, gray residue.

According to Matt Joseph, columnist for Skinned Knuckles and author of The Standard Guide to Automobile Restoration, that “gray residue” is Stage 2 of the process that fuel goes through as it goes stale. “Gasoline starts to go bad in about three months,” he said. “After a year or so, the Stage 1 deterioration turns it into a brown gel — after a decade or so, all you have is a gray residue. By that time, the car’s fuel system is ruined.”

The gray stuff left after years of storage is actually gum and varnish deposits in their final state. We’re more used to the brownish-red deposits that stain our beautifully restored vintage S.U.’s and Quadra-Jets after just a few months of winter hibernation. “If you leave gas in a car from fall to spring, it starts to smell funny,” Joseph explained. “Most people are familiar with the odor, but they don’t realize that the smell is the fuel going bad. It means that it has started to varnish up.” Eventually, gum and varnish will clog the fuel system. This in turn will cause hard starting. Deteriorated gasoline will eventually increase maintenance costs and even shorten the life of an engine.

According to Gold Eagle, a Chicago company that markets a popular fuel stabilizer called Sta-Bil, all fuels are made up of many different organic compounds. Over time, these compounds change and become new compounds that alter the characteristics of a fuel. Air, moisture and other elements in the environment create new molecules that oxidize and form gummy residues or varnish-like films that coat gas tanks and eventually clog up fuel lines and carburetors.

A few off-brand fuels use no oxidation inhibitors, but most brand-name gasolines have such additives that can protect stored fuel for a short time. Few car collectors realize that oxidation inhibitors in pump gasoline rarely work for more than 60 days and hardly ever more than 90 days. That means the fuel stored in the tank of that car you put away at the end of September was going stale by New Year’s Day.

Some people believe that running a gas tank low and then draining all the fuel before tucking a car in for winter will protect it. This is a big chore, especially if you own a bunch of cars. The only way to completely drain a system is to blow it out with compressed air. Draining and siphoning alone won’t get all the fuel out. In addition to the tedious work involved, you’d be wasting lots of expensive gas. You can’t store it, because that would be a fire hazard.

Draining a fuel system completely is also one of those procedures that solves one problem and creates another: rust. With bare metal in the tank and fuel lines exposed to air (and moisture caused by condensation), those parts will begin to corrode. Gaskets and seals may also dry out or crack, allowing the system to leak when refilled.

The best answer to this gasoline degradation is the use of a fuel stabilizer. There are many such products on the market, including those made by Gunk, STP and Gold Eagle, all of which have been manufacturing fuel stabilizers for decades.

Most gasoline stabilizers will prevent gasoline from going stale for between a year and six months, according to Larry Beaver, Ph.D., Vice President of Research and Development for Gunk. Most of the products intended for consumer uses contain “a specialty detergent designed to keep varnish and other materials safely suspended so that it doesn’t create gums and varnishes,” said Beaver. Where they differ, he continued, is in the amount of the stabilizer chemicals used in the product and in how much is needed to treat a given quantity of fuel.

According to Norman Berke, a research associate with STP Research and Development, ”The primary focus in fuel stabilization is to prevent or reduce fuel oxidation. Oxidation results in gums and gels forming in the fuel. When the concentration of these [gums and gels] becomes great enough, fuel jets, needle valves, fuel filters and fuel injectors can become restricted or plugged.”

Although there are a variety of minor differences in the major brands of fuel stabilizers, both Beaver and Berke agree that most reputable brands may be safely mixed in a single tank of fuel.

Fuel degradation is not the only challenge that car collectors who store vehicles for lengthy periods of time face. Earlier, we mentioned rust formation in a drained system. Joseph points out that a pre-1970 vehicle stored in an unheated area with a partially full gas tank is prone to the same problem. “Pre-1970 cars have non-sealed fuel systems that develop condensation as a car or truck goes through normal temperature cycles (cold at night and warm during the day),” Joseph notes. “Moisture is introduced into the system and any exposed surface area inside the gas tank or other parts can start rusting.” Fuel stabilizers — even those with emulsifiers — can only deal with a limited amount of moisture; their primary job is to keep the fuel from breaking down.

For this reason, vehicles should be stored with the gas tank as full as possible, leaving some room for normal fuel expansion on hot days. Add the fuel stabilizer according to the manufacturer’s direction, fill the tank with gas and be sure to start the engine to allow the stabilizer to flow through the fuel system. Follow this simple procedure, and in the spring you should be able to start and drive the car on the same gas you stored it with. On the other hand, Joseph points out that if you store a car for six months with the gas tank partly full, even if you put fuel stabilizer in, you should plan on draining the tank and adding fresh fuel.

Using a fuel stabilizer is an important part of winterizing your collector car agrees automobile restorer Chris Charlton, who cites bad oxidized fuel as the single biggest problem associated with storing cars for extended periods.

But using a fuel stabilizer shouldn’t be limited to your collector car. The gasoline in your lawn mower, snow mobile, snow blower, chain saw or boat—be it two-stroke or four-stroke–is just as susceptible to oxidation as the fuel in your collector car.

If you didn’t use a fuel stabilizer when you stored your car in the fall, it may not be too late. Buy one of the premium products available, add the recommended dosage to your fuel tank, start it up and run it for a few minutes. You may just save yourself a lot of work come spring.

John “Gunner” Gunnell is the automotive books editor at Krause Publications in Iola, Wis., and former editor of Old Cars Weekly and Old Cars Price Guide.