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Is premium fuel better for old cars?

What Fuel Should You Use in Your Classic Car?

If you’re thinking of buying a classic car, or you’ve recently bought one, you might be wondering what fuel you should use in it.

With the majority of high-octane leaded fuels axed for environmental reasons, it can be difficult to find the right one.

Older cars typically run on leaded fuels with a high octane rating, but since they were scrapped in the early 2000s, classic car enthusiasts have had to look for other alternatives to keep their motors on the road.

White convertible with red accents on a sunny day

In this guide, we look at why modern fuels containing ethanol are bad for classic cars and the best available alternatives:

  • Why are Some Modern Fuels Bad for Classic Cars?
  • Which Fuels Work Best in Classic Cars?
  • What Will Electric Mean for Classic Cars?

Why are Some Modern Fuels Bad for Classic Cars?

Cars built for lead-based fuels don’t 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.

Pure petrol fuels with a high octane level have almost been phased out in the UK, with only a handful of suppliers now offering high-octane fuel at the pumps. Old cars rely on this kind of fuel because they aren’t 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 isn’t a good match for older cars that aren’t built for this kind of fuel.

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As the government looks to clamp down on petrol and diesel cars, fuel suppliers have launched new fuels containing a greater quantity of ethanol. This means it’s now even harder for classic car owners to find a fuel with a low enough ethanol count for use in their cars.

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Fuels which contain ethanol are bad for classic cars for a number of reasons, including:

  • Ethanol is “hygroscopic”, meaning it absorbs moisture. This moisture can condense in the fuel tank and cause components to rust, especially when the car is stored for long periods.
  • Fuels containing ethanol produce over 30% less power than older types of petrol, so the performance of older cars not built to work with this kind of fuel can suffer.
  • Ethanol is a powerful solvent and can corrode materials like rubber and fibreglass, both of which are often found on classics.

Can I Use Redex Fuel Additives with E10 Petrol?

E10 petrol has arrived in UK fuel stations, replacing the customary E5 formula for standard petrol. The good news is, you can use Redex petrol fuel additives safely with E10 fuel, so you can continue to benefit from improved engine health and performance.

Simply add a shot of Redex each time you top up the tank.

It also provides an additional protective layer to prevent corrosion from the increased ethanol content found in E10 Petrol, which means that even if your car was manufactured before 2011 you can use E10 fuel safely by adding it as well.

Redex Petrol System Cleaner

Which Fuels Work Best in Classic Cars?

Although fuels containing ethanol aren’t good for collector cars, there are a few different options available when it comes to keeping your car on the road.

High-Octane Fuel

A handful of fuel suppliers in the UK do offer high-octane petrol, which is often billed as “performance-enhancing”. Designed for sports cars, these fuels have a high-octane rating that suits older engines, but be warned as some still contain up to 5% ethanol.

You can increase the octane rating of your petrol yourself by using Redex Power Booster – this helps you control the power levels yourself to get the right performance.

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Monochrome image steering wheel and interior of a classic car.

Standard Low-Ethanol Fuels

While high-octane fuel is preferred for classics, they can run perfectly well on lower octane petrol, especially if the ignition is adjusted to counteract the change in combustion rate.

But remember that many standard fuels on the forecourt now contain up to 10% ethanol, so you need to do your research and find one that’s got the lowest amount of ethanol you can possibly find.

When searching for different fuels, look for the ‘E’ sign which shows the percentage of ethanol in the fuel. For instance, E10 contains 10% ethanol, E5 contains 5%, and so on.


If you’re willing to sacrifice the authenticity of your classic in exchange for cheap, readily-available and environmentally-friendly fuel, converting it to run on LPG is an option.

LPG, which stands for Liquefied Petroleum Gas, is becoming more popular in the UK, with drivers favouring it for its affordability and reduced C02 emissions.

It can be quite expensive to have the fuel tank converted to accept the new fuel, but more car owners are choosing it these days.

Converting to Modern Engine

Many classic car owners simplify the problem altogether by converting to a modern engine system, so you can use standard fuel without any worries. Like LPG conversions though it can be expensive, so if you’d prefer to keep your car in its original condition then you’ll need to consider alternatives when you top up.

Lead Replacement Additives

If you own a classic car built for leaded fuel, you can either convert it, or take the easier option of using a standard fuel and adding lead to it with an additive like Redex Lead Replacement. 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.

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Redex Lead Replacement

What Will Electric Mean for Classic Cars?

In some ways, classic car owners face a race against time – and technological progress – to find sustainable and readily available sources of fuel with which to power their cars in the future.

Between governmental legislation and the rise of electric motoring, it’s becoming increasingly difficult for classic car owners to find compatible fuel at their local forecourt. And with super unleaded fuels likely to be on their way out in the next five years or so, the future of classic car ownership is looking less and less certain by the day.

There is, however, some hope on the horizon – not least VW’s continued efforts to begin producing the world’s first fully synthetic fuel. If successful, this ‘manmade’ fuel could provide a long-term solution the problem of diminishing fuel supplies, giving classic car owners a reliable source of fuel that doesn’t endanger their vehicles.

That said, the prospect of synthetic fuels has been met with some speculation by industry experts, and it’s clear that the UK government’s intention is to continue pushing towards electric motoring. It remains to be seen what this could mean for classic car owners in the long term, but it’s likely to translate into ever-decreasing availability of compatible fuels.

For more fuel advice and car maintenance guides, be sure to check out the rest of the Redex blog right here. Or, for our full collection of petrol and diesel fuel additives, visit our homepage today.

Premium vs. Regular

Sorry, that’s pretty much booo-gus.

Each gallon of gas that we pump from our local Quickie Mart is actually made up from as many as seven different ingredients. The exact amount of energy in each gallon of premium or regular gas will vary from company to company, depending upon what kind of additives they use.

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In actual fact, you’ll get a greater range of fuel economy between different brands of regular gas, than you will between the same manufacturer’s regular and premium gasses. Interesting, eh? We thought so.

Finally, here’s a nice irony: to increase gas’ octane rating, companies add ethanol, when they’re mixing up a batch of premium fuel. Interestingly, ethanol actually contains less energy than untreated gas, so the net result from the ethanol component is a reduction in your MPG. Other premium additives, however, have the reverse effect, and slightly increase your MPG. So okay, overall premium provides a very slight net increase in MPG, but it’s so slight that we swear you won’t notice the difference.

I always used the increased MPG that resulted from using premium as a justification to purchase it.

Too bad. Consider yourself better informed now, and stop lining the pockets of oil companies, okay?

Premium has special or extra detergents in it that are worth the added cost.

It’s true that premium gas does contain special or extra detergents, but in our opinion they’re of no additional benefit.

Our advice is to ignore any sales pitch about the super-special detergents that come in the premium-grade fuel.

These days, all of the gasoline from the major gas companies contain more than enough detergents to keep your engine clean. Period.

The only reason you might have a use for the extra detergents in premium, is if you have a noticeably dirty engine, and need to scrub carbon and other crud off engine components. (And, if you’re doing that, we’d instead suggest that you toss in one of the many fine engine additives.)

You said «major gas companies.» Is there a difference in the gas between the big names, and the El-Cheapo gasoline at my local Costco or Stupey-Mart?

There is. A number of years ago, some of the major auto manufacturers were ticked off with the deposits from gas that met EPA detergent standards. In other words, they were afraid they’d take the heat for problems, when their customer’s engines clogged up from the twigs and dirt that was getting deposited on their fine handiwork.

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So, they set their own guidelines, which they call «Tier 2.» All of the gas from the major gas companies meets the Tier 2 standards. The gas at your local Quickie Mart probably does not. The difference? In some tests, after about 10,000 miles, there was a minor amount of crud built up on engine components that ran exclusively on Quickie-Mart gas. Do we think this is an issue? Not really. But, would we advise running your car for 100,000 miles only on Quickie-Mart gas? Not if you’re concerned about the longevity of your vehicle. We recommend switching back and forth between Tier 1 and Tier 2 — maybe every other tank full — to keep your engine running clean.

I will void my warranty if my owner’s manual calls for premium and I use regular unleaded.

You might, but we don’t think so.

But, that’s just our humble opinion. If you use regular instead of premium, and your car calls for premium, there’s no way we can guarantee that your dealer won’t try to sneak away from taking responsibility for repairs.

But, if we had a vehicle that called for premium, we’d take the risk. There’s a big price difference between regular and premium. That adds up to quite a bit of money over the life of your car.

As a last ditch effort, print out this feature and show it to the dealer. Maybe he’ll come to his senses. But don’t hold your breath.

Using regular gas in a car designed for premium will definitely damage the engine.

We don’t believe that any modern engine that claims to require premium will be damaged by using regular unleaded judiciously. Neither do any of the sources we’ve checked with — including the American Petroleum Institute, the American Engine Rebuilders Association — even a chemist (who would rather go unnamed) at a major gasoline company.

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