Classic car engines were designed and built prior to the mid-70s ran solely on leaded gas. For the unsuspecting driving these vintage cars which are unrestored on unleaded fuel may cause serious damage to the engine. Why does it matter; isn’t gas just gas? Not any more as current fuels have dramatically changed over the past 30 years, and we need to take care of what goes into the gas tank to avoid damage and big repair bills.
Cars built for lead-based fuels do not work well with modern unleaded variants. Lead is needed to protect compounds in the fuel valves and without it, old engines can suffer serious damage and wear. Not only that, but ignition firing can be affected and may need to be reset and adjusted to work with different types of modern fuel.
In 1920, leaded gas was introduced to the motoring market as a main fuel for running cars. In the 1980s, it was decided that the increasing collective lead content was too toxic, and as such unleaded gas was introduced in the mid-1970s, and leaded gas was subsequently phased out and withdrawn from the gas market. Only a small percentage of gas stations still offer, and this potentially poses a problem for the vintage car owner.
Pure gas with a high-octane level have almost been phased out, with only a handful of suppliers now offering high-octane fuel at the pumps. Old cars rely on this kind of fuel because they are not built for modern alternatives, which can be far too abrasive in the fuel system.
Ever since the older-style of lead-based petrol was banned in 2000, fuel companies have provided standard unleaded which is mixed with a small quantity of ethanol. Ethanol is added to fuel to make it more environmentally friendly, but its corrosive properties mean it is not a good match for older cars that are not built for this kind of fuel.
Converting the Engine for Unleaded Fuel
Previously, the leaded compounds presented in the fuel provided the valve seats in the engine with a level of sustained protection. As unleaded gas does not provide this protection, problems begin to arise due to what is known as ‘valve seat regression.’ This is where the valve seats of the cylinder head are slowly worn away, causing the valves to regress back too far into the cylinder head.
The valves need to lose heat extremely rapidly, and they normally do so via conduction with the cylinder head when they close. If they regress too much, there is less contact surface area between the valve face and the valve seat of the cylinder head and so the valves are unable lose heat fast enough. This can result in the valves becoming “burnt out” – literally having holes and indentations burnt out of them. This can cause considerable damage to the engine. Interestingly it is often possible to run unleaded fuel in an unconverted engine for short periods of time, as the valve seats have in the past already been protected by the lead that was present in the fuel. This is known as ‘lead memory.’ However, be aware that you if your valves have been replaced at some point in the past, and new valve seats have been cut for them, then this ‘lead memory’ may have been removed.
If you wish to run on unleaded gas for sustained periods of time, then the best option is to have a machine shop perform an ‘unleaded conversion’ on your cylinder head. This will normally involve them removing the old valve seats and replacing them with special hardened alloy valve seat inserts – which tough enough not to suffer from valve seat regression. It should however be noted that, due to a change in octane number, when converting to an unleaded fuel, your engine’s timing will need adjusting. This is quite important as otherwise detonation can occur instead of a controlled combustion of the fuel and air mixture in the combustion chamber. Detonation, sometimes called ‘pinking’ due to the sound it makes, can literally ruin an engine.
The success of this sort of conversion can be subject to the configuration of the vintage car engine and should not be undertaken lightly. It is advisable to seek professional advice if you are seriously considering doing this. If you are concerned with reducing toxic car emissions, you might be able to retrospectively fit a two-way catalytic converter – but again this is subject to the type of engine and exhaust line in your vintage car.
Just Unleaded Fuel
If drastically converting your car engine is not an option, then there are other steps that you can take. The simplest option by far is to opt to run your car on unleaded fuel only. Classic cars can run for a while on purely unleaded petrol, but if the car is frequently used, as aforementioned, eventually the cylinder block or head will become vulnerable to corrosion. For this reason, if you choose to run your vintage car on just unleaded petrol and want to drive it frequently, then you will need to use a lead replacement additive. They are designed to offer the protection that leaded fuel once did, and are quite easy to add, if you are adept at measuring and following instructions! Most gas stations or car parts stores stock a range of these additives. As there are a range of alternative additive ingredients on the market, it would be advisable to contact a specialist or your car club to find out which is the best for your vintage car engine.
Lead Replacement Additives
It contains additives which lubricate and protect the fuel system, safeguarding it against the harmful effects of ethanol while guaranteeing excellent performance. Lead Replacement is specifically designed for use in classic and vintage cars and should be used in every tank to maintain your car’s performance and protect vulnerable components like valve seals.
Finally....
When buying a classic car, it is important to know the condition of the engine as to whether it original to the vintage car, or has it been restored and updated to run on modern fuels.
None of this is true. I have friends with old classic cars and have run them on unleaded gas for decades without a problem. That additive is just a con to rip people off.