Modern fuel and E10

Most pump petrol in the UK and Europe now contains up to ten percent ethanol, sold as E10. The E-Type was designed when petrol contained none. The general effects of ethanol on older fuel systems are well established; the details for any one car are less tidy.

What ethanol does

Ethanol can attack some older rubber compounds, seals, gaskets and diaphragms, causing them to swell, harden or crumble. It absorbs water, and the water it carries can promote corrosion in steel tanks and lines. It can also loosen old deposits inside a system and carry them into filters, jets and float valves. In a carburettor, where small drillings, a float needle and soft seals do the metering, any of these effects can show up as flooding, leaks or erratic running.

A car in storage is not a car in use

The same fuel behaves differently depending on how the car is used. A car driven weekly keeps fuel moving, uses it while it is fresh and exposes components to it briefly. A car laid up for winter holds the same fuel in the tank, lines and float chambers for months, which is when ethanol's water absorption and its effect on soft parts do their slow work. Owners storing a car over winter commonly fill the tank to reduce condensation space and drain or empty the carburettors, though the archive offers this as widespread practice rather than as a Jaguar recommendation.

What to do about it

Higher-octane grades in some markets contain less ethanol, and ethanol-free fuel exists in a few places. Fuel system components renewed today can usually be had in ethanol-tolerant materials, which is worth specifying whenever hoses, seals or float valves are replaced anyway. None of this requires panic; it requires knowing what the fuel is and how the car is used.