Lead replacement petrol
What are the options?
Leaded four star petrol was withdrawn from sale in 2000 and the product that replaced it - Lead Replacement Petrol (LRP) - went the same way in 2003 as sales were so low. What are the options if you drive a car designed to run on leaded petrol?
If you have a pre-1992 car it's important to find out if it can run on 95-octane Premium Unleaded petrol, the normal grade sold in the UK. Check with a dealer or the manufacturer.
Converting your car
For pre-1992 cars designed to run on leaded petrol there are two possible problems if they are run on unleaded fuel.
There is the loss of about two 'octane numbers' from the older four-star leaded and the LRP that replaced it. This should barely be noticed although ignition timing might have to be reset to avoid any tendency to detonation (or 'pinking').
Ignition timing is usually checked as part of the routine servicing so the extra cost of re-setting should not be great.
Secondly, if the engine has valve seats cut directly into a cast-iron cylinder head or block, the loss of the protective effect of the lead compounds means that under conditions of hard, high-speed use, erosion of the seats can occur.
If the seats recede by more than the pre-set valve clearances, the valves will overheat and severe damage will result.
The long-term answer is to have hard-alloy valve seat inserts installed, or even an exchange head fitted.
Conversion devices
There are advertised fuel-line or fuel tank devices that claim to allow the use of unleaded petrol in otherwise unconverted cars. We have not been able to establish the science behind these claims, and do not recommend their use.
Solutions for unconverted cars
If you don't want the expense and possible hassle of getting the head converted you have three basic choices:
1. Use a proprietary branded additive
We can't say that valve seat recession can't happen with these additives because of the enormous range of engines out there in conditions ranging from pristine to near collapse.
In normal or moderately hard road use however, the valve seat protection afforded by these additives is perfectly satisfactory, and engine life will be just as good as with leaded petrol.
Take care, as mixing and dose-rates can be quite difficult to get right in small amounts. Once you've chosen an additive stay with that brand rather than swapping between products.
2. See what happens on unleaded only
Not completely daft, in that driven reasonably for limited mileages, the valve clearances will not be taken up between services, so with moderate care no harm should result.
Look out for loss of compression or reduced valve clearances, in which case you must take action right away.
3. Continue using leaded four-star
When four-star was withdrawn from sale a concession to the regulations allowed 0.5% of petrol sales to be leaded, for 'characteristic' vehicles. But there are now only very small quantities sold for historic vehicles by licensed garages who are members of the Federation of British Historic Vehicle Clubs (FBHVC).
Other firms (Elf and Carless) may be able to supply fuel at racing events.
Extreme hard use tests have shown that the valve seat protection afforded by leaded petrol is superior to that of LRP additives but the advantage isn't great and isn't needed in normal road use. Having the option of leaded petrol for racing unconverted vintage cars could be useful though.
It makes no sense to drive long distances to buy leaded, or to mix it with additised fuels if it's hard to find.
There are strict and sensible regulations controlling the storage of petrol: it may only be kept in the vehicle's normal petrol tank or as a few litres in approved spare cans.
Special cases
There are some specialist high performance cars that need high octane fuel. These were made in the days of 100-octane fuels, but could get by on 97-octane leaded and then LRP. Going to 95-octane unleaded just possibly could cause trouble, even with the ignition retarded.
The long-term option is to lower the compression ratio - at some power loss - but with benefit to engine life. Usually a new set of pistons can achieve this; engine specialists can advise.
There are some proprietary 'octane boosting' fuel additives but their affect on different fuels can be unpredictable.
Two-strokes, without poppet valves, don't have a problem, and in fact lead replacement additives should not be used with two-stroke mixes. Sleeve valves have a different lubricating method, and will not be affected.
Suitable additives
There are several proprietary lead-replacement additives available for 'DIY' dosing of unleaded petrol.
Additives may be phosphorus, sodium, potassium or manganese based – and are quite satisfactory used at the correct dosing rates in appropriate vehicles.
The following fuel additives were found satisfactory in engine durability tests set up by the Federation of British Historic Vehicle Clubs:
- Millers VSP Plus, (manganese)
Millers Oils Ltd. Freephone 0800 281 053 - Red Line Lead Substitute, (sodium)
Opie Oils 01209 215164 - Superclean Zero Lead, (potassium)
Morris Oils 01743 232200 - Castrol Valvemaster & Valvemaster Plus (phosphorus)
Castrol Ltd. 01793 512712
It's best to choose one product and stay with it, though some inter-mixing will be inevitable at times.
Lead compounds
There have been lead compounds such as tetraethyl lead offered for sale, for the user to dose unleaded petrol with 'real lead'. Though the process is certainly effective, handling such toxic chemicals is far too dangerous to be undertaken at home.
Why lead was used
Lead was used as an additive in petrol from the 1920s through to the beginning of 2000 when European legislation discontinued normal sale and distribution of leaded petrol (otherwise known as four star or BS4040).
Lead allowed the development of higher 'octane number' fuel (the higher the number, the greater the resistance of the fuel to uncontrolled burning in the engine, or 'detonation'), and was also discovered, later, to have the property of protecting valve seats from wear.
Leaded fuel was withdrawn because lead is a cumulative toxin, found to affect human health adversely. Modern refining methods can provide the necessary fuel quality (octane) without added lead.
2 August 2011