The oil change place my wife took our 2014 Mazda 5 to told her she HAD to get the fuel system cleaned ($80.00) to avoid engine warranty issues regarding corrosion due to the 10% ethanol in the gas here. I think this is just upselling for them. Is there an issue with the ethanol added to gas?

 

Alcohols (methanol or ethanol) are added to gasoline to promote more complete combustion (as they contain oxygen) to reduce carbon monoxide and soot (i.e. pollution).

Methanol in particular does carry problem to the fuel system of car that is not designed for alcohol-blended fuel, i.e. rubber/polymer swelling, corrosion, loosened deposit, etc. So, in this regard your garage is not wrong.

However, ethanol poses much less problem than methanol and if the car is designed to take ethanol additive and you have not just recently switched from pure gasoline to 10% ethanol, it might have been a bit of upsell.

More info: https://en.wikipedia.org/wiki/Oxygenate

 

this post is correct for cars that were NOT designed for alcohol fuels. so, perhaps if a car is more than 10 years old. this is a 2014 my. and, pure bulls**t to try to sell a fuel system cleaner, than probably costs them 10 bucks or less. and can be bought at any store for 10 bucks or less. and is not needed. if the need for profit is that great, i would look long and hard at whatever else was charged for, and also find another place to take my car. an independent garage should build a relationship with a car owner, so they trust the shop, and keep bringing the car back.

 

Overall, I agree with Keninn's post. They are trying to take advantage of a woman who probably isn't that well versed in automobiles.
With that said, I have recently had a CEL issue with my 2004 Mazda3 along with a rougher than usual idle. I bought two cans of a Berryman B12 product I've had good experience with before that costs less than $5.00/can.
Berryman B-12 Chemtool 0116 - Carburetor, Fuel System & Injector Cleaner | O'Reilly Auto Parts

I poured them into two consecutive fill-ups and no more problem, not that it was an instant fix. It did take a few miles (about 100+ miles) and some time, but the car is much better now.
Because injector cleaners are usually pretty aggressive, it's not a good idea to use them on a short, regular basis. They can be quite hard on high pressure surfaces like the tips of the injectors, for example. Used too often and the injectors will wear out prematurely.

 

i also use fuel system cleaner. i just wanted to point out that in present day cars, there is no such thing as corrosion in the fuel system from ethanol. and 80 bucks is gouging

 

Agreed! But for those that don't know any better, $80 is profitable!! LOL