midrange

Hi there.

We bought a 98 2.8 A4. We have always been told to use 91 or better octane fuel so we did in our last 2.8 audi.

This one the previous user said he ALWAYS used reg 87 Octane fuel and never had an issue. We told him you should always use 91 or better and he said it wouldn't matter.

Well of course we read the manual and it says use ONLY 91 or better. So obviously he was wrong.

I'm guessing it has a higher compression ratio to which is requires the higher octane. Does this mean he may have worn the rings out faster or done any damage?

cheeba

Tip #1 - don't buy a car from someone that is admittedly ignorant of their vehicles. You're just asking for trouble.

Your car can detonate on lower-octane fuel; but, it does have knock sensors, and should pull the timing to compensate. However, this isn't to say that there has not been any damage done. If it runs fine, then there's no major damage to the engine internals. Sure, there may have been some additional particle wear internally, but there's no way to know how much with disassembling and measuring the engine components. Unless you're going to rebuild the engine, there's not much point in worrying about what's already done; just minimize any future damage, and get the most life out of what you have.

The real risk of running fuel that is lower in octane rating than is recommended is that you can destroy your engine in a single detonation.

midrange

ok. well thats what i figured.. Its changed to 91 now andplan to use that from now on.

That tip you gave is what i followed. This car is from the original owner and he has every single maintenance record, and everything that has been done to that car from the day it was drove off the lot.. including the original sales receipt.. Judging by the way the records have been kept, i figured he took very well care of this car. He said his mechanic is who said reg fuel would be fine. We shall see.

Corrado_Guy

You can run lower octane fuel and it won't necessarily damage the motor but the mileage will decrease a bit and you won't have as much power. These motors are designed to run all over the world with different grade fuel so you can do it but you will get some knocking as mentioned above and this will not help the motor. To get the cleanest burn and longest life you should use the minimum recommended octane or better. Where I live the highest you can get is from Chevron only and that is 94 octane which they are threatening to drop even as I write. You can literally feel the difference in 87 and 91, try putting $10 of low octane in the car and drive it a little hard and then do the same with 91 or better and you will feel it. I also have a VW VR6 and a G60 and both of those motors change with the type of fuel used but I always use the highest octane available. If you don't have knock sensors or you aren't manually advancing your timing you won't get much out of higher octane but higher compression computer controlled motors can make the most out of it. As the motor is running it is continually tweaking the timing and fueling so the better fuel you can give it the better it will run. My A4 has a GT28RS turbo so I am forced to use high octane it that car no matter what which makes me sad thinking of the only supply of 94 octane drying up.

Another downside to lower octane fuels would be that they contain a certain amount of ethanol which the higher octane fuels do not. Some people say this is good but I don't buy it, from what I have heard it is basically a cheaper product that can be cut into the fuel to make it cheaper to produce and still make reasonable power. Ethanol based products don't burn as well so you don't get as much punch on each firing unless you modify the car a bit from factory.

These are just my opinions based on loose facts so if you know differently please post because I would be interested in hearing some facts about fuel.

a4rob

read this

http://www.usatoday.com/money/autos/...emiumgas_x.htm


pretty key quote from porsche:

All Porsche engines are designed for premium, too, but it's not available everywhere. "Our cars must be able to drive all over the world, and so we are able to run on regular," says Jakob Neusser, director of powertrain development at Porsche's research and development center in Weissach, Germany. "You don't have to feel that a mechanical problem or anything else will happen" using regular gas, even in the highest-performance, regular-production Porsches.

mksu19

CONSUMER GUIDE GASOLINE OCTANE FACTS and MYTHS

EDIT: I thought I read somewhere in the manual that says it's ok to run lower grade fuel (-91Octane ) if premium grade is unavailable. I'll try to look it up and post it here later.

midrange

Thanks so much for all your replies.. This has made me feel somewhat better of the fuel used in my car. I will stick with using 91 although we have 94 here in town. But unless i go boost which i won't, 94 won't be nessesary.

Thanks again. Now to my Oil problem in another thread.

cheeba

Except for that you're now concerned with the previous owner running the incorrect fuel, and the incorrect oil in the car. Reread Tip #1 and think about it a little deeper.



At least you posted a disclaimer It is generally the higher-octane fuels that contain more ethanol, since it is has an inherently higher octane-rating. Ethanol contains less joules per unit volume, so is less fuel efficient per unit volume than gasoline; however, it is capable of ultimately making more power than gasoline due to its higher octane rating, and the fact that you're pumping more mass through the engine (since ethanol requires higher fuel-flow rates).



Randomly Googled stuff?

I'd love to see a document where Porsche states that it's okay to run 87 octane fuel in a GT2 RS

midrange

I do not require your used car purchasing tips. thank you. I didn't just jump on the first audi i came across. I did the research and searched for 2 months before making my purchase. The guy drove this car for 12 years on red 87 octane.. I was inquiring the fact the hand book said to use 91.. I was investigating it a little bit.. Thanks for your concern

adamstasiak

This is "YAYKS!"

Well, at least you know what has happened to the car in the past.
Compression test would tell you if he damaged the engine.

This is like buying a new house and taking an axe to polish it a bit from the outside.