Spaceframe

I know the manual says to use 91 octane fuel, but 87 may be used at a reduction in engine performance. In my area most gas station offer only 87 regular and 89 mid grade options. A few stations have 91, but they are harder to find. Although 91 is the preferred, are their owners out there using 89 as the primary fuel for their cars?

I'm hoping to have my car in a few weeks so I am trying to scout out where I am going to fill up.

rsilvers129

I am testing 87 now. I can't tell a difference in performance or sound, so I am tracking fuel economy of 93 and 87 and will post my results. I will then compare any reduction in fuel economy to the savings in fuel cost, and see if it is worth it.

BTW, I have seen two people say it is harmful to the engine *even* if the engine adapts to the fuel. I don't believe them though.

Spaceframe

My understanding is that it is harmful if you get knocking. Otherwise it is a performance issue of the engine. There have been threads on this in the past.

89 is .30-.40 more than 87. 91 is .80-1.00 more. That is a big difference in cost if I don't need it.

rsilvers129

If any forum member has a dyno I would love to see a HP test.

Or someone could go to the drag strip.

heisnuts

You also have to factor in if the gas mileage is affected by using lower octane fuel. I suspect that you will find lower octane will produce lower mpg. Then there is the potential of causing harm/excessive wear on the engine, which I guess is not a big issue if you are only leasing for 3 years and plan on giving it back after the lease. But if you were the person looking to buy a 3 year old car off lease and you knew one had 91 for its 3 years and another used 87 or 89 for the 3 years, which one would you buy? For the life of me, I have never understood why this becomes such a big issue with just about every car maker who designs their cars to run on 91 or higher, especially when the car in question usually costs over $50K.

RickObe

I've been running 89 in mine since new, 1.5 years. No adverse affects noted. I ran 89 in my 2012 Q7 for five years prior to that. Again, no adverse affects noted.

Spaceframe

Getting higher mpg is certainly a valid argument but the value can be easily calculated. Let's say I am getting 18mpg using 87. At 30% higher price I would need to get over 23mpg with 91. That seems like a stretch to me, but maybe it does.

If there is a potential for harm and excessive wear on the engine why does Audi say it "will slightly reduce performance" in their manual? This can be interpreted as both economy (mpg) and power. Their comment on engine damage is regarding knocking which is well known. But if you don't get knocking, it doesn't solve economically in mpg and any loss in power is acceptable what is the value of using the higher octane? So I am wondering if 89 octane fits this bill. I'm just asking if anyone has experience with using mid grade as their primary fuel choice.

Spaceframe

Thanks, good to know.

heisnuts

The problem is you will really never know if there is any damage being done or not. I guess in the big picture it really is not that big of a deal since a lot of people who buy a new Q7 do not keep that same car over 5 years or 60K so if there are any problems that develop later on in life it will be someone else's problem to deal with. However, if you were looking for a used Q7 and you knew one had been using 91 it's whole life and the other had been using 89 it's whole life, would it affect your decision at all?

NABS4

There is no more heat energy per unit volume of "premium" gas than there is in "regular" gas. I use 91 in the summer (greater chance of pre-detentation with warmer ambient temps) and 87 in the winter (don't care about 5 hp loss because the roads are usually icy anyway). In my experience reported better fuel economy using higher octane gas are anecdotal and not based on reality (energy capacity of the fuel).