Lead Replacement Petrol
What are the options?
Leaded four star petrol was withdrawn from sale in 2000 and now the product that replaced it has gone the same way.
Lead replacement petrol (LRP) is essentially a 97-octane (super) unleaded petrol with an additive to give the valve seat protection that some cars need.
By mid 2002 LRP accounted for only 2.7% of total fuel sales, and since the end of 2003 it has only been available at a few specialist outlets hoping to keep something no-one else has.
If you have a pre-1992 car it's important that you find out whether or not 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 to be run on premium unleaded.
Firstly, there will be a loss of about two 'octane numbers' from the older four-star leaded and the LRP that replaced it. This will generally be barely noticed although ignition timing might have to be reset to avoid any tendency to detonation (or 'pinking').
A check of the ignition timing is usually part of the routine service schedule, so the extra cost of re-setting should not be great. Give clear instructions to the garage when booking in for service.
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 hence do not recommend their use.
Solutions for unconverted cars
For the short term, the owner of a 'leaded only' engine has three basic choices.
1. Use a proprietary branded additive
The favoured option.
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 action must be taken 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 relatively few suppliers and the fuel's more expensive.
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.
There are about a hundred filling stations that still sell leaded four-star and the current locations can be obtained from www.leadedpetrol.co.uk (new window).
Other firms (Elf and Carless) may be able to supply fuel at racing events.
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 have been getting 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.
In the short term, use Super Unleaded, with an additive if required. There are some proprietary 'octane boosting' fuel additives but their affect on different fuels can be unpredictable. Some earlier electronic ignition modules cannot be reset for lower octane fuel, and are expensive to replace.
Some engines will present particular problems in fitting hardened valve seat inserts, either because the seats are very close together or in the case of non-detachable cylinder heads, because access is difficult. If inserts can't be installed, you are back to the three options of using an additive, seeing what happens or finding a supplier of leaded four star.
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 – these will increasingly be found in accessory shops and filling stations.
Additives have been in use in Germany, Austria, Switzerland and New Zealand for some years with no reports of problems, though there are reservations about the effect of a sodium based product on turbo-charger blades.
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 British Historic Vehicle Clubs:
- Millers VSP Plus, (manganese)
Millers Oils Ltd. Freephone 0800 281 053 - Red Line Lead Substitute, (sodium)
Delta Oil Ltd. 01476 861 195 - Superblend Zero Lead, (potassium)
Superblend Lubricants Ltd. 0116 291 1700 - Castrol Valvemaster & Valvemaster Plus (phosphorus)
Castrol Ltd. 01793 452 222 - Carplan Nitrox 4-Star (potassium) & 4-Lead (manganese)
Carplan Ltd. 0161 764 5981
In general, it's best to choose one product and stay with it, though some inter-mixing will be inevitable at times.
Where the vehicle manufacturer originally recommended the use of, for instance, one tank of leaded petrol to four tankfulls of unleaded, if you are using an additised fuel the additive should be used in every fill.
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.
Lead is a cumulative toxin, affecting the nervous system in extremely small doses – it is absorbed as a vapour through the skin, lungs and eyes. To take such material into the home environment is totally inappropriate. Only dedicated industrial toxic chemical handling equipment can avoid the risk of adverse health affects.
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.