Unleaded Petrol and Pre-1986 Cars

Many vehicles built before 1986 were designed to operate on leaded fuel. However leaded fuel was withdrawn from the Australian market due to environmental and health concerns over lead pollution.

This information sheet will assist owners of pre-1986 vehicles to choose a suitable alternative fuel for their vehicles.

The lead compound added to leaded petrol did two things. It was a cheap and easy way of raising the fuel’s octane rating (the fuel’s resistance to engine knock) and it protected the engine’s valves and valve seats from excessive wear.

Depending on the engine’s design, it may have needed leaded fuel for either one or both of these purposes. However some pre-1986 vehicles are capable of operating on unleaded fuel.

To check if your vehicle can operate on an unleaded fuel go to the Australian Institute of Petroleum Lead Replacement Petrol Guide.

If you find your vehicle on the list, there are a few things you should keep in mind. The information contained in the list has been supplied by the vehicle manufacturers and is based on a correctly maintained and tuned engine in original condition. Certain repairs, modifications or normal engine reconditioning processes may alter the engine’s sensitivity to a lower octane rating fuel. Incorrect engine tune settings and carbon build-up in combustion chambers can also affect the engine’s ability to operate correctly on ULP.

Vehicles shown in the guide as suitable for premium unleaded (PULP) should not be operated on ordinary ULP, as major engine damage can result.

Vehicles not listed will require the use of a fuel with a suitable octane rating and a lead replacement additive. A vehicle’s octane requirement will be listed in its owner’s manual. Lead replacement additives are available from service stations and auto parts suppliers. They must be added to the vehicle’s fuel tank at each fill.

If pinging or engine knocking is audible, especially under load, it may be possible to slightly retard the ignition timing to overcome this. We recommend you discuss this with your mechanic and have him/her perform this operation. However significant variation to recommended ignition timing settings should not be made to allow use of ULP. Fuel consumption, performance and emissions may be adversely affected by retarding ignition timing.

If the engine is found to ping or knock under load the need for a higher-octane fuel is indicated.

Pinging or knocking in any engine should not be neglected as the potential for engine damage is great. If you aren’t sure if your engine is pinging, consult a reliable mechanic.

In theory it’s possible to modify early engines to allow them to operate satisfactorily on normal unleaded fuel, however such re-engineering will usually be costly and will involve major engine repairs or a complete overhaul. Such modifications will often involve reducing the engine’s compression ratio and installing valves and seats made from materials that are sufficiently hard and wear resistant to not require a valve protection agent in the fuel.

In some cases obtaining suitable replacement parts or performing the necessary modifications to the existing components may effectively, in practical terms, preclude conversion.

If you intend to pursue this course of action we suggest you discuss your particular requirements and likely costs with a reputable engine reconditioner.