The usage of 20 per cent ethanol-blended petrol in vehicles could lead to a 2-5 per cent drop in fuel efficiency, depending on the type of cars, according to automotive industry experts.

In the midst of social media debate over the impact of E20 fuel on vehicles, automotive engineers working with some of the major automakers, whom PTI spoke to, said that in older vehicles, which are not E20 compliant, there could be erosion of gaskets, fuel rubber hoses and pipes in the long term, but not immediately.

"There can be a drop in mileage ranging from 2-5 per cent, depending on the type of vehicle. This is purely because of the lower calorific value of ethanol compared to petrol," said an expert requesting anonymity.

Earlier this month, the Oil Ministry clarified that "the critiques suggest that E20 causes a 'drastic' reduction in fuel efficiency are misplaced". However, it did not state the percentage drop in fuel efficiency.

"The efficiency drop (if any) in E10 vehicles has been marginal. For some manufacturers, vehicles have been E20 compatible from as far back as 2009. The question of any drop in fuel efficiency in such vehicles does not arise," the ministry had said.

The ministry also stated that "vehicles tuned for E20 deliver better acceleration, which is a very important factor in city driving conditions. Additionally, ethanol's higher heat of vaporisation reduces intake manifold temperatures, increasing air-fuel mixture density and boosting volumetric efficiency".

On August 4, the ministry, in a post on X, said: "Ethanol, being lower in energy density than petrol, results in a marginal decrease in mileage, estimated at 1-2 per cent for four-wheelers designed for E10 and calibrated for E20, and around 3-6 per cent in others".

When contacted for comments, leading automakers Maruti Suzuki and Hyundai Motor India declined to comment.

A Tata Motors spokesperson said, "Our vehicles are E20 compliant".

Another expert said, "E20 usage will not have any impact on engines of compliant vehicles, as the materials are tuned for it. However, in vehicles, which are not E20 compatible, there could be erosion of gaskets and fuel rubber hoses and pipes in the long term, but not immediately".

The government has taken steps to blend petrol with 20 per cent ethanol extracted from sugarcane or maize as a national programme, aimed at cutting emissions and raising the income of farmers.