Cleaner fuel, lower mileage: Will ethanol blend hurt your car engines?

Ethanol can promote corrosion of metal components, and strip deposits from fuel systems, potentially clogging filters and lines. So higher the blend, higher the chances of old engines getting affected

India’s push towards finding a substitute of petrol as a fuel in vehicles is progressing at a rapid pace with its aspirational ethanol-blending programme increasingly gaining positive momentum. As part of its green fuel policy, the government is aggressively pushing for ethanol blending, starting with E10 (10 per cent ethanol) and now moving toward E20 (20  per cent ethanol).

 

On July 24, Petroleum and Natural Gas Minister Hardeep Singh Puri said that ethanol blending in petrol has strengthened India’s energy security and brought notable environmental gains. But while these claims are largely backed by data, concerns are mounting in other quarters. Automobile manufacturers have flagged technical risks and efficiency losses, especially with higher ethanol blends like E20. Consumer groups too are wary of paying more for fewer kilometres.

   

What is ethanol and how is it used as fuel?

 

Ethanol (ethyl alcohol) is a renewable, biodegradable fuel made by fermenting biomass, usually sugarcane, corn, rice, cassava or other crops. As a fuel component, it is blended with petrol (gasoline) in proportions like E5 (5  per cent), E10, E20-E25, up to E85 or even E100 in specially designed engines. It lowers greenhouse-gas emissions and reduces reliance on fossil fuel imports.

 

What is ethanol blending and how do blends work?

 

Ethanol blending means mixing ethanol with petrol in predefined ratios for use in internal-combustion engines. Common blends include E10 (10  per cent ethanol), E15, E20, E25, or even E85/E100 for flexible-fuel vehicles. Engine control systems or fuel sensors adjust fuel injection and ignition timing to compensate for ethanol’s different properties. Most cars sold in the US since model year 2001 can safely run on up to E15, but E85 and full ethanol require specifically designed “flex-fuel” vehicles.

 

What is India's most recent ethanol blending policy?

 

India's National Policy on Biofuels (notified in 2018) under its Ethanol Blended Petrol (EBP) Programme set a 20 per cent target by Ethanol Supply Year (ESY) 2025-26. In early 2025 India reached that target ahead of schedule, achieving an average blending of roughly 20  per cent by March 2025, saving an estimated Rs 1-1.5 trillion in foreign exchange, as Oil Minister Hardeep Singh Puri announced in June this year.

 

The government is now set to target a new goal of 30  per cent blending by 2030. In Maharashtra, a central change in July 2025 allows use of food grains (maize, broken rice) alongside molasses, boosting production capacity and potentially raising blending to 27  per cent. India is also exploring incentives like lower GST on high-ethanol blends and encouraging flex-fuel or E27/E30 capable vehicles.

 

A federal programme to encourage second-generation bio-ethanol from agricultural residues (rather than valuable food crops) was launched in 2019 with nearly Rs 200 crore funding. But as of mid-2025 only a single demonstration 2G plant is operational, and pricing for 2G ethanol remains unresolved.

 

What are the concerns against ethanol blending?

 

Despite its environmental and economic rationale, ethanol blending has drawn concern from automotive industry groups and consumers, particularly around fuel efficiency and vehicle performance.

 

For standard petrol engines designed for up to E10 or E15, ethanol can be used without modification. In most formulations, only minor changes in fuel input and ignition timing are necessary, which modern engine control systems will accommodate. Automakers recommend suitable fuel systems and materials at high blending levels (E20-E25) to ensure seals and hoses resist the corrosiveness of ethanol, as ethanol is hygroscopic (it absorbs moisture) and can corrode metal components, breakdown rubber and plastic parts, and remove deposits from fuel systems, thereby potentially clogging these components (filters and lines). High ethanol blends may also make it increasingly difficult to start the engine cold, along with very rough idle.

 

Ethanol blends affect fuel efficiency

 

According to a 2021 report jointly released by NITI Aayog and the Ministry of Petroleum and Natural Gas, using E20 fuel leads to noticeable drops in fuel economy. The report estimated that for vehicles designed for pure petrol (E0) and calibrated for E10, a switch to E20 results in 6-7 per cent loss in fuel efficiency for four-wheelers, 3-4 per cent loss for two-wheelers, and 122 per cent loss even for newer four-wheelers designed for E10 but calibrated for E20.

 

These figures have prompted concerns among vehicle users, especially in the two-wheeler and low-cost car segments, where fuel efficiency is a key consideration for running costs. With no parallel reduction in retail prices of ethanol-blended fuel, some users feel they are paying the same for fewer kilometres.

 

The Society of Indian Automobile Manufacturers (Siam) has identified these efficiency losses and recognized that, through proper engine adjustments, including hardware and tuning changes, one can cut down performance decreases. However, until there are affordable widespread flex-fuel compatible vehicles, the average consumer will continue to carry that cost.

 

The NITI Aayog report suggested a form of tax incentive on E10 and E20 to offset the decreases in mileage the consumer would experience, but no large-scale policy has emerged so far.

 

Some fuel retailers have expressed operational issues, particularly the need to upgrade their infrastructures for storage and dispensing systems that can handle ethanol blends without contamination or corrosion; others view fluctuating ethanol prices and variable supply of agricultural feedstocks as long-term sustainability risks.

 

How are two- and three-wheelers affected by ethanol blending?

 

Most two- and three-wheelers in India and elsewhere are petrol-powered small engines. They are seldom tested or certified for high ethanol blends. Using E10 is generally safe, but higher blends (above E10) may require engine tuning or modified parts, which are not yet standard in India. To date, no national approval or retrofit programmes for two- or three-wheelers for E20+ exist. Automaker readiness remains limited, and regulatory guidelines for two-wheelers and autorickshaws for blends beyond E10 are lacking, raising concerns that widespread use of higher blends without adaptation may risk performance and durability.