Ethanol, Stale Fuel and Storing a Classic

Fuel is the part of a winter lay-up that gets least attention and causes the most tedious spring. Battery problems announce themselves; a gummed-up carburettor waits until the first warm Saturday.

Modern pump fuel does two distinct things to a stored classic, and they need separating because only one of them has a bottle-shaped solution.

Two problems, not one

Fuel goes stale. Petrol oxidises. Lighter fractions evaporate, the rest polymerises, and what is left behind is the varnish that blocks jets, gums float needles and coats the inside of a carburettor. This is the old problem, it existed long before ethanol, and it is what stabiliser addresses.

Ethanol attracts water. Ethanol is hygroscopic — it pulls moisture out of the air above the fuel. This is the newer problem and stabiliser does very little about it.

Conflating the two is why people treat a tank, store the car, and still find corrosion and a car that will not run cleanly in spring.

What water in the tank actually does

Past a certain water content the ethanol-water mixture stops staying in solution and separates out as a distinct layer at the bottom of the tank.

That matters because of where it sits. The fuel pickup draws from the bottom, so the first thing the engine gets on startup is the layer that will not burn properly. The layer is also corrosive and it is resting directly on steel.

On a modern car with a sealed tank and a short lay-up this rarely becomes a problem. On a classic with a vented tank, a season of temperature swings, and possibly some existing surface rust, it is exactly the mechanism that turns a stored car into a fuel-system rebuild.

What actually helps

In order of how much difference each makes:

Fill the tank. Free, and it addresses the mechanism directly. Less air space means less moisture available to condense, and fuel covering the tank walls means less bare steel exposed to it.

Use ethanol-free fuel if you can get it. This removes the water-attraction problem and the material-compatibility problem simultaneously, which no additive does. Availability varies considerably by region.

Add a stabiliser, and add it before the last drive. The additive needs to reach the carburettor or injectors, not just sit in the tank — so treat the fuel, then run the engine long enough to draw treated fuel all the way through the system. Adding stabiliser to a tank on a car that is then parked immediately treats the tank and nothing downstream of it.

Check the flexible lines. On a car whose rubber predates ethanol blends, the fuel hoses are a consumable. Perished lines weep rather than burst, so the symptom is a smell and a stain rather than anything dramatic.

Materials that predate the fuel

This is the part specific to older cars, and it is why generic storage advice does not transfer.

Fuel hoses, carburettor float needles, accelerator pump diaphragms, cork gaskets and some tank sealing compounds were all specified for fuel that contained no ethanol. Modern equivalents exist for essentially all of them and are worth fitting during any fuel-system work you are doing anyway.

The usual signs that something in the system has not coped:

• A fuel smell in the garage that was not there before
• A float chamber that overflows after the car has stood
• Staining or softening on a flexible line where it meets a union
• Fine debris in the filter that was not there last year

None of those are emergencies and all of them get worse if the car goes into another lay-up untouched.

Draining, and when it makes sense

The instinct to store a car dry is reasonable and usually wrong for a single winter.

An empty tank is an air-filled tank, and air brings moisture to bare metal with no fuel film protecting it. For a seasonal lay-up, full and treated beats empty comfortably.

Draining becomes the right answer for genuinely long-term storage measured in years, for a car whose tank is coming out anyway, or where the fuel in there is already suspect and you would rather not circulate it.

Spring, and the order to do things in

Fuel problems and battery problems present identically from the driver's seat: the car will not start. Establishing which you have before reaching for anything saves a great deal of time.

• If it cranks slowly or not at all, it is electrical. Start with preventing a dead battery in winter storage, and if the battery keeps going flat rather than merely being flat, measure the parasitic draw.
• If it cranks healthily and will not fire, it is more likely fuel or ignition, and this page is the relevant one.
• If it fires and runs badly, suspect the carburettor rather than the tank — that is stale fuel varnish doing what it does.

A jump pack that spins a big engine but never gets it to catch is telling you the same thing, which is covered in compact jump starters for a V8 classic.

The rest of the lay-up routine — the battery, moisture, brakes, tyres and the things worth not bothering with — is in classic car winter storage.