Is Regular Petrol Damaging my Car?

Words by Peter Read, Chairman of the Club’s Motoring Committee

The petrol available at UK filling stations currently contains up to 5% ethanol (E5) but policymakers are being lobbied by environmentalists and farmers to increase this to 10% (E10). They claim that only older and historic vehicles will suffer from incompatibility issues but this is not correct: ethanol can, and does, damage much newer vehicles. Although delayed in the UK, E10 has already been adopted by various EU member states and is especially widespread in North America.

Meaningful moves to reduce the environmental burden of the motorcar have to be welcomed, as long as they do not create technical issues which could undermine the ecological goal. ‘Diesel-gate’ is an obvious example of when unrealistic, politically-set, targets overtook technical reality.

Car manufacturers are being quoted as calling E10 “harmful” if a car is misfuelled. The German motoring organisation, ADAC, reports that a single tankful “can cause serious, lasting damage” should it be used in a non-compatible vehicle. Reports from various lubricant and fuel/oil additive experts over the years have revealed that the increasing percentage of bio-fuel present in petrol (and diesel) poses a number of technical challenges, even on vehicles that are stated as being compatible.

Debates in the UK Parliament about non-ethanol-compliant vehicles have tended to revolve around ethanol having a deteriorating effect on certain metal and rubber components in historic vehicles, rather than discussing the effect on similar parts fitted to the vast majority of newer cars. However, it is not right to assume that no modern vehicles, including those certified for E10, will experience negative consequences from running on the fuel. Last year, Dr Ivo Wengraf of the RAC Foundation matched vehicle manufacturer data with DVLA registration data and identified that modern cars from MG-Rover, the Volkswagen Group, Mazda, Nissan and Toyota are likely to be the most numerous E10-incompatible vehicles on our roads in 2020.

So, what does ethanol do?

Ethanol has corroding effects on metal surfaces and dries-out rubber hoses. Corrosion of the fuel tank and brass carburettor parts are the main challenges for historic vehicles. Rubber fuel lines also become brittle, split and leak fuel. Owners of other machinery (such as boats and certain motorcycles) have had issues with fibreglass fuel tanks, because ethanol within the petrol dissolves the resin.

Many newer vehicles have direct injection petrol engines (GDI) which introduced high pressure technology to increase power and reduce CO2, and these are less tolerant of fuel specifications deviating from those used when the car was new. Engines from the noughties seem to suffer especially from material incompatibility problems in their high-pressure systems. It is thought that aluminium components within the high-pressure fuel pumps on some GDI vehicles are vulnerable to ‘corrosion attack’ and ADAC found that this can be triggered after a single refuelling with E10. The most common example of modern fuel system E10 incompatibility rests with the first generation FSI engine used by the Volkswagen Group brands, many of which are still on UK roads.

Aside from acting as a fuel, petrol possesses a lubricating element for the mechanical components that are in contact with it. As ethanol lacks any lubrication properties, this has a negative effect on the durability of fuel system components, unless, of course, extra additives are blended with the fuel at the refinery to compensate. The makers of the renowned Wynn’s Professional range of additives reported that ethanol-blended petrol also tend to be more acidic. The resultant contamination promotes incomplete combustion that causes higher exhaust emissions, poor running, catalytic converter failure and sticking inlet valves.

Ethanol also holds water in suspension and is hygroscopic. Potentially, the greatest weakness of ethanol blended fuels, therefore, is their susceptibility to separate into a petrol (top layer) and an incombustible water-ethanol gloop (bottom layer). The issue is not helped by ethanol’s ability to hold water in suspension up to a certain level before it separates. One study revealed that natural degradation of ethanol blended fuels occurs within 4-6 weeks, leading to incomplete combustion and the creation of larger deposits that also contribute to engine running issues.

A suggested way to avoid these issues is to brim and empty the fuel tank regularly but it is feasible that certain plug-in hybrid cars with a reasonable electric-only range (such as the Mitsubishi PHEV) may not empty their fuel tanks before the fuel either ‘goes-off’, or the separation process begins. The issue of fuel separation, therefore, may become more of a real-world problem for the latest and forthcoming Plug-In Hybrid cars that can travel greater distances in electric-only mode. So, this is not just an issue for older vehicles.

So, what should you do?

There is limited, and often conflicting, advice out there and so it is difficult to point at specific information. Clearly, the best source is the manufacturer’s handbook or website but this is unlikely to be exhaustive. So, what do I do?

• I try to empty the fuel tank (without running out!) before refilling to the brim.
• If I am leaving the car for any length of time, I try not to leave much petrol in the tank. Interestingly, this is the opposite of every piece of advice I used to receive, prior to the introduction of ethanol, which was to keep the tank full to minimise any condensation in the tank.
• Finally, I always use Esso Supreme. Esso is one of only two fuel suppliers (Jet is the other) which states that its premium grade contains no ethanol. Even Esso is not able to guarantee this in Devon, Cornwall and Teesside!

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