E20 fuel efficiency: ARAI finds up to 6% mileage loss, rules out engine breakdowns

Mileage can drop by 2-6% in vehicles running on E20 petrol, according to extensive testing by the Automotive Research Association of India (ARAI).

However, the government-backed automotive testing agency says the higher ethanol blend does not cause engine failures or major performance issues in compatible vehicles, with long-term trials covering 40,000 km in passenger vehicles and 20,000 km in two-wheelers finding E20 to be safe for regular use. 

ARAI’s findings, based on studies conducted with original equipment manufacturers (OEMs), show that while ethanol has a lower energy content than petrol — leading to a modest reduction in fuel economy — drivability, startability and acceleration remain unaffected. The tests also recorded significant reductions in carbon monoxide (CO) and unburnt hydrocarbon (HC) emissions. 

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The durability study found that metal and plastic fuel system components are compatible with E20 fuel. However, some older rubber hoses, seals and gaskets in vehicles not originally designed for E20 may degrade faster and require earlier replacement. 

Explaining the mileage impact, ARAI Director Reji Mathai told ANI that ethanol has a slightly lower calorific value than petrol, which naturally results in a small reduction in fuel economy. 

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“The studies were done along with the OEMs… to assess the impact of E20 compared to E10. We understand that ethanol as a fuel has a slightly lower calorific value. So the blend also has a slightly lower calorific value.” 

He said the fuel consumption tests were carried out under controlled laboratory conditions, with chamber temperatures maintained and vehicles tested on dynamometers to accurately isolate the impact of the fuel.

According to Mathai, ARAI tested vehicles ranging from 3-4 years old to nearly 10 years old, with the observed drop in fuel consumption varying between 2% and 6% depending on the vehicle. 

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ARAI is now evaluating E25 petrol (25% ethanol) to assess its impact on fuel efficiency, engine health, long-term durability, emissions and operating costs. According to a May 2026 report by The Times of India, the study will involve 60,000-70,000 km of real-world testing and will also examine whether vehicles certified only for E10 or E20 can safely operate on E25 without increased maintenance costs or significant performance degradation.