Hi,

I am considering getting a 2011 A4 2.0T . However, I'm a bit reluctant for the increased cost of the premium fuel (I drive a lot). I'm wondering if anyone has had any extended experience running lower octane fuel than the recommended 91.

My current car is a 2002 1.8T Jetta. 11 years later, and I've never put anything higher than 87 Octane in it, and the engine runs like new (everything else is getting old). 91 Octane was always recommended but I never used it. Is it the same case for the A4? Anyone done it?

 

Not a problem as it only takes a few HP away. You will get a little better mileage with 91 but not enough to pay the extra costs. We have put 15K miles on our 2009 and it has not caused any problems.

 

Seems you would get some knocking...no?

 

Caranddriver wrote an interesting article about this a while back. I believe they tested an M3 with 87 octane. They never noticed any problems/knock

Cars nowadays have engine knock sensors and i guess the timing can be advanced to adjust to the lower octane fuel.

You will lose hp.

I've heard that 91 octane also burns cleaner. So by using 87 you could worsen the carbon buildup issues that this car already has. I've never tried anything but 91. Seems like some have done it for 15k miles though.

 

I'd stick with 91 octane. A few bucks here and there for better MPG and better burn is more than worth it.

 

Funny thing is you won't know the difference except for your fuel bill.

 

First look at the math of it. Remember that fuel economy isn't about mpg but dollars spent. Things have changed in the last 10 years. 91 is still usually 20 cents per gallon higher than 87, but the price per gallon has gone up.

Today with gas prices at around $4 a gallon (give or take), and assuming 20 cents per gallon for premium going in a car getting 20 mpg, the net effect on fuel economy is around 0.5 mpg (I think this number goes up as the car's fuel economy goes up but I haven't done the math to confirm it). Ignoring good/bad for the car, if using 87 octane costs you even 1 mpg then you're falling behind; not getting ahead.

 

I have often wondered about the whole gas thing as well. My manual says not to go below 87...and that premium was recommended not required. I'm nervous because I just bought my 2013 a4 a month ago today..so for now, I am sticking to Premium. I am just using my gas buddy to find the cheapest premium in town!

 

the thing is it causes ping/pre ignition specially now on summer making it hard on the engine , there will be a power lost as to how much not sure but there is always a power lost and the catalytic suffers the most as well as your spark plugs, for each time you use lower oct your timing well be pulled back by the computer. that's all there is to it.

high oct gas is for high compression engine and turbo / super charge engine du to the high temperatures and compression inside the chamber.

 

On average it's about 10 cents more for 91. (in my area at least). With 91 you will gain around 3-4mpg. We will use 3mpg as the base.

Gas is 4.00 for 87, 4.10 for 91. You buy 30 dollars worth.

87: 7.5 gallons
91: 7.31 gallons.

We are going to assume you average 25mpg on 87, and 28mpg on 91.

So, you have the following distances traveled.

87: 187.5 miles
91: 204.68 miles

see the difference?



Now, since some areas have different gas prices, I will use the same formula but with a 20cent increase for 91 fuel. Just to be on the safe side of things.

You have $30 to spend on gas.
87 = 4.00
91 = 4.20

87: 7.5 gallons
91: 7.14 gallons

Same 25 mpg base for the 87 fuel, 28mpg base for the 91 fuel.

87: 187.5 miles
91: 199.99 miles



So, with this said you should use the recommended 91 fuel in your car. It will also burn cleaner and build up less carbon in your engine.

Hope this helped. Please use the correct fuel!