Drop in fuel efficiency on my Yamaha R15: Is ethanol blending to blame?

Ethanol blended fuel can affect a vehicle's FE, especially if the vehicle is not specifically rated.

BHPian sasta_rider recently shared this with other enthusiasts:

Finally, someone came up with the same thought I had been pondering about since few months now.

I have noticed a downfall in the FE of my 2022 R15 v4 over the past year. I do not calculate FE random times; every time I refuel, I fill the tank completely and feed the odometer reading, total fuel cost, and cost per liter to the 'Fuelio' app, which then calculates the FE figures based on this input.

Below is the chart from which you can figure out how it has reduced during my ownership till date (but no regrets from my end, because the machine is just beautiful in every possible way):

Also, below is the stat showing the best & worst FE along with other information, for nerds who are interested:

The best FE was during the breakfast ride towards Nandi hills, conducted by Vinayak Yamaha (Domlur). Poor me had to maintain speeds between 60-90 kmph, which is the sweet spot for this engine to obtain best FE.

The worst FE was during the Jan-2025 ride towards Goa. I still do not know why so low FE in spite of me getting the engine oil replaced and chain maintenance done, previous day of the ride.

I did some research to learn about how far India has achieved the ethanol blending in petrol and found that we have achieved the target of 10%. The target of 10% ethanol blending has been achieved much ahead of the targeted timeline of Nov-2022. Link for the government's press release is here.

Upon further Google search, I could conclude this:

Ethanol blended fuel can affect a vehicle's FE, especially if the vehicle is not specifically rated. Ethanol has a lower energy content than pure petrol, which can lead to reduced FE. Additionally, ethanol can cause issues in engines not designed for it: like higher carbon build-up and faster degradation of rubber components. While modern engines are generally more tolerant of ethanol blends (like the R3, which is E10 rated), non-rated vehicles might still experience a decline in performance and FE, which is exactly why I had been hitting my head against the wall. This is just a contributing factor.

Apart from this, my R15 usage involves:

• Frequent long rides at higher RPMs and triple digit highway cruise.
• Commute through dusty environment (especially at Bengaluru), which clogs the engine intake filter in turn leading to comparatively reduced performance which does hit FE.
• Poor quality fuel (well, we can not test petrol at every outlets, but can be cautious as much as possible).
• Improper gear shifting.
• Chain slack: a loose chain can cause inefficient power transfer from the engine to the rear wheel along with jerking and uneven acceleration. Personally, I have experienced this too when I neglected maintaining the chain slackness due to work/family commitments.

I am still concerned, in the coming years, how will our beloved machines survive these stringent norms being implemented by the GoI! What I can say is: pamper your bikes/cars/any machine for that matter, as much as possible so that we keep the engine revving!

Hope this post clears the confusion around ethanol blended petrol I guess!

Ride safe!

Sud.

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