I have a 99 A6 Quattro 2.8L, and I was wondering whether I should use premium gas or not. The owners manual says that premium gas is recommended, but I can use regular gasoline if there is no premium gas available.

Anyone's input?

 

I would never just use regular, middle grade, 91?, should be fine. or is it 89? Anyway I wouldn't use the Regular, but you should be fine with the middle stuff.

 

these cars are built to run on premium. sure you can use regular because of the knock sensor, it wont knock. over time it will ruin the catalytic converter if use is consistent. i just spoke to my uncle in texas who has a z3. we were talking about something, and he told me he was using regular. then i told him he was crazy for doing that, n he finally realized why he already replaced his cats twice in 5 years.

 

Ultimately it comes down to driving patterns.
Also, you have to take into consideration the gas prices. Now it is of course a "high time" for motorists, due to the drastic drop in gasoline price. However, until 4-5 months ago the difference in price from regular (87 octane) to premium (91 octane) was beyond significant - 30-40 cents/gallon; in some cases/locales even higher than that.

If someone drives his/her Audi a whole lot (daily commuter), it may make sense on the long run to drive on regular gas, with some additives/gas treatment used each or every other thank.
Let's assume (for the sake of a simple example) that person needs ONLY one tank/week. 52 weeks/yr x 8 dollars (difference in price for 20 gals) = $ 416/yr
In 5 years you can offset the price of replacing 4 CATs.

Conversely, if someone uses the Audi just for pleasure trips, it may make more sense to go with the recommended premium (91 octane) gas.
Again, ultimately it comes down to driving patterns and... the size of the pocket.

So "crazy" is just a relative term, no pun intended. It solely rests with the eyes of the beholder.

 

Never knew about the knock sensors... learn something everyday.

 

well yes the price can offset the replacement of 4 cats over 5 years, but the cats arent necessarily the only things that can get damaged. i cant recall exactly, but i remember a member here acquired $1300 in damages to the engine alone for using regular gas over a two year period. i think valves, etc.? not sure.

 

I'm not the proponent of using regular gas in a vehicle that's recommended to drive on premium.
I was just trying to give you a different angle as to why (maybe) your uncle is using regular.

 

I would never put 87 octane in a turbo charge engine with high compression, you will stress out the engine and cause problem as the engine age. The knock sensor will hold back the timing but it is design to advance the timing slight until it detects knock and then back off again. If you are using regular gas, this cycle will repeat itself over and over again. That slight knock before the knock sensor back off on the timing will cause problem for your engine further down the line.

 

I hate to say it, but I use regular. I have the 2.7t, not the 2.8, though. The 2.7t is a lower compression engine than the 2.8. I drive almost exclusively on the freeway commuting. I get better gas mileage with regular than I did with premium. Yes, when I get into the throttle, I can feel the timing being retarded. However, 99.9% of the time I am at part throttle which does not need premium. I DO add gas treatment every other tank, just to keep the system clean.

With a higher compression 2.8, I would be more hesistant to go this route.

Bob

 

The 2.7T has a compression ratio of 9.3 to 1 compare to the 2.8L which is 10.3 to 1, but the 2.7T also has a turbo boost of 8-9 PSI. That makes the 2.7T engine much higher compression than the 2.8. Like I said, I would never use 87 octane on a Turbo charge engine. There are some turbo charged engines that are coming out on the market soon that are design to run on regular, but the Audi 2.7T engine is not one of them.
By the way, using 87 octane gas doesnt mean you need to add gas treatment to keep the engine clean. All grades of gas have the same amount of cleaning agent in them with the exception of Shell V-power and a few other premium brand which add more cleaning agent into their premium gas.