If you own a car built before 1986 you must determine which of the fuels now available is suitable for it.
The lead compound used in petrol did two things:
- It raised 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 one or both purposes.
However, some pre-1986 vehicles will operate satisfactorily on Unleaded (ULP) or Premium Unleaded (PULP). To find out if your car is one of these check with its manufacturer.
If your car is not suitable for ULP or PULP, a fuel with a suitable octane rating and a lead replacement additive is needed.
- A car’s octane requirement will be shown in its owner’s manual.
- Lead replacement additives are available from service stations and auto parts suppliers.
Some important points:
- The manufacturers recommendation is based on a correctly maintained and tuned engine in original condition. Repairs and wear can alter an engine's sensitivity to a lower octane fuel.
- Vehicles listed as suitable for PULP may be damaged if operated on ordinary ULP.
- 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.
- Significant variations to ignition timing settings will adversely affect fuel consumption, performance, and emissions.
- If the engine pings or knocks under load a higher-octane fuel is needed.
- Pinging or knocking must not be ignored as engine damage can result.
- If you aren’t sure if your engine is pinging, consult a reliable mechanic.
- Lead replacement additive must be used at every fill as it has no residual effect.
In theory early engines can be modified to allow operation on unleaded fuel.
- Such re-engineering will usually be costly and will involve major engine repairs or a complete overhaul.
- We suggest you discuss your requirements and likely costs with a reputable engine reconditioner.
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