Want the steps, not the theory? Our long-term storage prep checklist is the do-this-in-order version. This post explains why each of those steps is on the list.
Three items dominate every conversation about storing a collector car: a battery tender, tire flat spots, and fuel stabilizer. The rules get repeated — hook up a maintainer, bump the pressures, treat the tank — and they are right. But owners who know only the rules tend to misapply them: leaving an old trickle charger connected all winter, overinflating to a number someone quoted at a car show, or pouring stabilizer into six-month-old gas. All three problems share one origin. A stored car is not idle; it is a system with slow chemical and mechanical processes running in it, and driving is what normally interrupts them.
Batteries: two drains, then permanent damage
Where the charge goes
A stored battery loses charge two ways at once. Self-discharge is an internal reaction that runs whether or not anything is connected; a healthy flooded lead-acid battery commonly loses on the order of 3–5% of its charge per month at room temperature, an AGM rather less. Parasitic draw is the bigger problem: every modern car keeps modules awake or lightly sleeping — alarm, keyless entry, telematics, body control — and the residual current is typically a few tens of milliamps. A 30-milliamp draw is 0.72 amp-hours a day, roughly 22 amp-hours a month; on a 70 amp-hour battery that is about a third of capacity per month before self-discharge takes its share. It is why a car that started fine in November is dead in January, and why the same battery in a 1968 car would have survived the winter.
Why a flat battery is worse than an inconvenience
Resting voltage approximates state of charge: roughly 12.6 V and above is full, 12.4 V about 75%, 12.2 V about 50%, 12.0 V about 25%. Damage begins near the top of that range. Discharging converts active material into lead sulfate, which is normal and reverses on charging; what does not reverse is what happens when that sulfate is left standing. Small, soft deposits gradually recrystallize into large, hard ones that no longer convert back readily. The battery does not come back merely flat in the spring — it comes back with permanently less capacity.
Temperature pushes from both ends: self-discharge roughly doubles for every 18°F (10°C) of temperature rise, while a deeply discharged battery — whose electrolyte has become more like water — can freeze not far below +20°F and crack its plates and case.
Maintainer, not charger — and yes, you can leave it connected
An old-style trickle charger delivers a roughly fixed current and never stops; over months it overcharges, gasses off electrolyte, and corrodes the positive grids. A smart maintainer in the 1–2 amp class charges, drops to a float around 13.2–13.4 V, then cycles back on only when voltage sags. So: a multi-stage maintainer can stay connected all season; a dumb charger should not stay connected overnight. Match the chemistry — AGM and lithium starter batteries need the correct mode, and a lithium battery charged on a lead-acid profile can be damaged. Prefer the maintainer to disconnecting the battery, which on a modern car dumps adaptations and settings.
Flat spots: rubber has a memory
What a flat spot actually is
Tire rubber is viscoelastic, so it does not behave like a spring: under sustained load it slowly deforms, and when the load comes off it recovers slowly rather than instantly. Park a car and the contact patch flattens under a corner weight that never moves, so the tread-area cords and the rubber around them take a set in that shape — the thumping you feel over the first few miles. Cold makes it much worse, because performance tires commonly use nylon cap plies and nylon readily takes a set while cooling under load. An unheated garage through a Denver winter flat-spots tires that a temperate building would not.
Temporary or permanent?
Most flat spots are temporary: twenty to thirty minutes of driving puts heat and flex back into the tire and it returns to round. The permanent case is specific — a heavy car, low-profile summer tires, low pressure, cold, and months without moving. Then the set stops being elastic and the tire never fully recovers.
What actually reduces it
- A modest pressure increase. Adding 2–5 psi above placard pressure (Hagerty's guidance; tire makers including Michelin hold that placard pressure is fine) stiffens the carcass and limits contact-patch deflection. Never exceed the sidewall maximum, and reset pressures before the first drive. The much-repeated advice to add 10 psi or more is not supported by tire manufacturers.
- Cradles or curved storage pads. These spread the load over an arc instead of a flat line, attacking the mechanism rather than resisting it — the right answer beyond about six months.
- Movement. Rolling the car a quarter tire-rotation every few weeks means no patch of rubber holds the set long enough to keep it. A facility with a repositioning routine is doing exactly this. Jack stands are not the shortcut they look like: unloading the tires trades a tire problem for a suspension one.
Fuel: three failures wearing one name
"Old gas" is shorthand for three distinct processes, and stabilizer only addresses some of them.
1. The light ends leave
Gasoline is a blend, and its most volatile components — butane, pentane, similar light hydrocarbons — are what let a cold engine start. They are also the first to evaporate out of the vapor space and through the evaporative emissions system. What remains is flammable but harder to light, which is why old fuel produces long cranking rather than a bang. Untreated pump gasoline, especially E10, begins measurably losing volatility in as little as 30–60 days.
2. Oxidation makes varnish
Gasoline's reactive components — olefins in particular — combine with oxygen to form peroxides and then heavier, sticky products: the gums and varnish that glaze injector tips, block carburetor passages, and leave a lacquer film in fuel rails. Warmth accelerates the reaction, as do trace copper and zinc from fuel-system metals, which catalyze it.
3. Ethanol collects water
Ethanol is hygroscopic — it pulls water vapor out of the air above the fuel and holds it in solution. E10 carries only a limited amount, on the order of half a percent by volume at room temperature; past that the mixture phase-separates, dropping a corrosive layer of ethanol and water to the bottom of the tank — precisely where the pump pickup sits. Hence the real argument for a full tank: no vapor space means little air to supply oxygen for oxidation or water for the ethanol to absorb, and little cool surface for condensation.
What stabilizer does, and what it cannot
A stabilizer is a package, not one chemical: antioxidants that interrupt the oxidation chain, metal deactivators that tie up the copper and zinc catalyzing it, corrosion inhibitors that coat tank and line surfaces, and dispersants that keep whatever forms suspended. Used correctly it keeps fuel serviceable for roughly 12–24 months instead of a couple of months. The limits follow from the mechanism: it prevents degradation but cannot reverse it, so adding it to fuel that already smells like varnish accomplishes nothing, and it neither removes water nor re-mixes a phase-separated tank. It also has to reach the whole system — add it before the final fill-up, then drive 5–15 minutes so treated fuel circulates through pump, lines, rails, and injectors.
The mechanisms side by side
| Problem | Mechanism | Accelerated by | What stops it |
|---|---|---|---|
| Battery capacity loss | Parasitic draw plus self-discharge, then hard sulfate crystallization | Heat; module count; a weak cell | Multi-stage maintainer, float 13.2–13.4 V, correct chemistry mode |
| Tire flat spots | Viscoelastic set in the contact patch; nylon cap plies set while cooling | Cold; low pressure; heavy car; low-profile tires; duration | +2–5 psi, cradles, repositioning, stable temperature |
| Hard starting | Loss of the light, volatile hydrocarbons in the blend | Warmth; vapor space; time | Full tank, stabilizer, shorter terms |
| Injector and carburetor deposits | Olefins oxidizing into gums and varnish, catalyzed by trace metals | Warmth; oxygen in the vapor space | Antioxidant and metal-deactivator stabilizer |
| Tank-bottom corrosion | Ethanol absorbing water until the mixture phase-separates | Humidity; partial tank; temperature cycling | Full tank, ethanol-free fuel, corrosion inhibitor |
Temperature is the variable underneath all three
Read the table down the "accelerated by" column and one factor appears in every row. Heat speeds self-discharge and fuel oxidation; cold sets flat spots and freezes discharged batteries; cycling between the two moves air and moisture in and out of the tank. A car sitting through August in Las Vegas and a car sitting through a Denver winter fail in opposite directions, and neither fails the way a car in a building held at a steady temperature does. That is the honest case for climate control over a heated garage: stability, not comfort. Our comparison of climate-controlled versus standard indoor storage covers the humidity side of the same argument — a separate mechanism again, with corrosion rates climbing once relative humidity passes roughly 60%.
It is also why a facility's service list is worth reading literally. "Battery tending" should mean a multi-stage maintainer matched to your chemistry and checked on a schedule, not a charger on a shelf; "tire care" should mean cradles or a repositioning interval, not a pressure check at move-in. Those are among the practices we look for before listing anyone — see our verification standards, or browse collector car storage by city.