E20 petrol in E10 vehicles may damage hoses and seals, report flags: What it means for you

India's shift toward higher ethanol-blended petrol may come with unintended consequences for older vehicles. A study by the Automotive Research Association of India (ARAI) has found that running E20 petrol, which contains 20% ethanol, in vehicles designed for the lower E10 blend can cause gradual deterioration of rubber components in the fuel system, including hoses, gaskets, seals, and O-rings, according to a report by Times of India.

The study, which has not been made public but has been used as a reference by the government and automobile manufacturers, flagged that these components "may need replacement" after extended exposure to E20 fuel.

At the same time, the study found no adverse impact on metallic parts across the vehicles tested, and emissions from E10-compatible vehicles using E20 fuel remained within legally prescribed limits.

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Engine performance: A mixed picture

The ARAI study also assessed engine durability in four-wheelers, and the findings were not uniform across manufacturers. For one original equipment manufacturer, testing over 400 hours produced no issues, with engine performance remaining acceptable on E20. For a second manufacturer, however, a "thermomechanical failure of exhaust valve was observed in the engine(s) tested cumulatively for 809 hours."

People with knowledge of the findings told The Times of India that factors unrelated to E20 fuel could also have contributed to the valve failure in the second case. Experts involved in vehicle testing noted that engine durability assessments are typically conducted over approximately 2,000 hours, making the duration of testing a significant variable when interpreting the results.

Separately, the study examined a Bharat Stage-IV engine, finding its performance remained acceptable with E20, while an "issue was observed with BS-VI turbo-charged engine after 265 hours of durability."

Two-wheelers hold up better

The picture for two-wheelers was considerably more positive. Engine durability tests conducted across three manufacturers found no issues, with the study concluding that "performance is acceptable with E20 fuel" in this category.

Fuel efficiency takes a small hit

Across the vehicle types studied, fuel consumption on E20 was found to be approximately 2% to 6% higher compared with E10, though the extent of the increase varied depending on the model. For everyday users, this means marginally more frequent refuelling, even as E20 is positioned as a greener and potentially cheaper option over the long term.

The findings add a layer of nuance to India's ethanol blending programme, suggesting that while the transition to E20 is broadly viable, older vehicles and certain engine configurations may require closer monitoring and, in some cases, component replacements over time.