OldCowboy

I am the owner of a new 2015 Audi A4. The owners manual recommends 91 octane fuel, but it is well recognized that the vehicle will run quite nicely on regular (87 octane) fuel, although with slightly lowered performance.

Now I'm not one of those people who takes my vehicles to the track and am willing to accept a few percent less performance if it saves me money at the pump. So I did a few checks on fuel mileage of 91 octane vs 87 octane gasoline. A pattern quickly developed where 91 octane fuel gave me between 8-10% greater highway mileage than 87 octane fuel. I should probably note at this point that at least 90% of my driving is on highways at 60-75 MPH.

In SW MO, there is a 30 cent per gallon premium for 91 octane gasoline. This is true whether the price of 87 octane is $1.79 (yesterday's price) or $3.89. So, from an economy standpoint, it only makes sense for me to buy 91 octane when it will result in a lower cost per mile than 87 octane. Assuming a 10% improvement in gas mileage with 91 octane, the only time 91 octane gives me better fuel economy is when the price of 87 octane is $2.99/gal or higher. When 87 octane is $2.99 and 91 is $3.29 the difference in price is 10%.

Above $2.99/gal with a 30 cent difference between 87 and 91 octane, my cost per mile is lower with 91 octane. At today's price, $1.79 for 87 and $2.09 for 91 octane, I would have to achieve 17% greater mileage with 91 octane to make it as economical as 87 octane. So, I'll continue to use 87 octane until the price rises to $2.99.

shs92645

These cars can run on 87, but in no way do you experience the power or efficiency that the engine has to offer. The longer you have your car, the better the gas mileage gets - you should average 28 or 29 mpg with over 30 on the highway - actually 32-34 is not uncommon. In addition, these engines are prone to carbon buildup and therefore high octane fuel from a top-tier brand that has detergents should save you headaches down the road. Your car cost you either side of 40K...and is turbocharged...cutting back on the gas just doesn't make any sense.

Nostromo

It's a shame when someone buys a nice German turbocharged engine and puts 87 octane in it. Probably need to read up on what octane really means.

Nostromo

It's a shame when someone buys a nice German turbocharged engine and puts 87 octane in it. Probably need to read up on what octane really means. You really ought to be putting 91+ all the time. They don't just put that sticker on the fuel door for giggles.

jagtoes

If you feel OK with it then do it. It won't hurt the engine and if you are using a brand gas they all have detergents in them regardless if it is 87 or 91 octane.

Macallan21

+1


By running 87 octane in your car. It is going to run like a dog. It will not accelerate as quickly, and you risk a lot of damage to oxygen sensors and such in side the engine. By all means, go ahead and save $100/yr by not using 91 octane. A new O2 sensor will probably run you $500 with labor.

I filled up a half a tank of 87 at New Years because I was on E-0miles purposefully. The station was $1.99 for 87, and $2.79 for 91. I didn't have enough gas left to drive down to another. My car HATED accelerating on the highway. And it's usually very easy to pass vehicles.

roger_1

+2

I didn't buy an Audi to accelerate as though I were driving a Corolla.

OldCowboy

The misinformation spread on this forum is sometimes astounding. Allow me to quote from the 2015 A4 Owner's Manual, page 207: "Your vehicle may also be operated using unleaded regular gasoline with a minimum octane rating of 87 AKI/91 RON. However, using "87 AKI/91 RON octane fuel will slightly reduce engine performance."

So, please, tell me again how using 87 octane is going to damage my oxygen sensors.

Note to moderator: Please do not delete this post like you did the last one.

E92MPower

Come old cowboy, don't you know every person on here is an expert? LOL. I would simply keep an eye and ear on the engine. As we all know, fuel quality can and does vary a bit from brand to brand and station to station. Based on that assumption, your A4 could suffer detonation. My current daily driver an Acura TL "recommends" Premium 93 octane. I experimented a bit using 89 and noticed the same results as you did. I said, let me try 87 octane and experienced knock and a very noticible drop in performance along with a check engine light. For me since I tend to keep my vehicles for a while I subscribe to the over-maintenance program and that includes only using top tier 93 octane fuel. I may even try some 100 octane race fuel in the A4 since this will be my first FI vehicle I'm excited to play a bit.

However, saving money is always a good thing. Keep it up, it's your car and please continue to share your findings as to what the long term affects are.

Out of curiosity are you buying or leasing the vehicle?

SFV A4

Over the years (decades actually), using lower grade octane has been known to mess up oxygen sensors and clog injectors. This has been seen on a wide array of cars, and usually after a long duration of using the lower-grade octane. While such studies and observations have not been written in stone by auto manufacturers, it's generally been recommended to use the higher octane numbers the factor recommends in order to avoid the CHANCE of future problems as the miles pile on. In other words, it's up to you, but the past twenty years has shown a connection with engine problems combined with lower octane numbers. I wouldn't take such a risk, considering the high cost of engine repairs after a warranty has expired. Plus the added mpg's and snappier performance are big bonuses.