Gas Octane
 

Will I notice any ill effects if I use an 87 or 89 octane fuel in my 07 A8? Now that I'm running the heate,r the trips to the gas station are getting too frequent and I've noticed if regular goes down in price, the good stuff barely budges.

That is not good idea. Computer would retard ignition in order to prevent knocking, causing power loss and consumption increase. That would offset any savings. On the long run it will hurt engine.

Can't it also cause an issue with the cats too?

I'm wondering if you have something else going on. Running the heater shouldn't have any perceptible difference in your MPG unless of course you are starting your car up half an hour before you leave. Colder weather does hurt your MPG but even that shouldn't significantly hurt your MPG. You may loose a couple of miles per gallon but any more than that I would be concerned. I think you may want to get some things checked out. How much worse is your MPG, 2 or 10? Also, if you are worried about MPG I think you bought the wrong car. There are a lot of things this car does well but being easy on gas isn't one of them. You may be happier with an A4 with the 1.8L or 2.0L. Being cheap and going with low grade is only going to cost you in the end.

I must confess that I do get terrible MPG in the winter time but that is only because I am having a blast and driving it HARD. I also like to pre-heat the car and aggressive snow tires don't help either. We got 6 inches of snow last night and I almost called in sick to work so I could go out and play. My last fill-up I got 8.5MPG. But hey, it was worth every penny.

Thanks for the feedback

That was fun! Attachment 83204

That was very fun. We have another 3 inches on top of the 6 inches I woke up to this morning and the plows haven't been out. I think I'll take a long lunch and have a little more fun. How could you not love snow and drive an Audi? They are made for snow. Especially with the extra long wheelbase of the A8L.

You can also wrap it in your garage and wait summer to drive it. ;)

Winter mileage often decreases...
 

not just w/ the added (richer mixture) time to warm up and cat light off, but particularly because of mandated winter fuel formulations in many areas that reduce the effective power you get from each gallon of fuel.

if you have a smart phone, i recommend downloading the Gas Buddy app to find the cheapest gas in your area...

to give you an idea of the money this app can save you, i did a search while typing this...it searched approx 45 gas stations in a 3 mile radius for premium (93) gas prices

the highest prices were:
texaco: 3.79
texaco: 3.69
valero: 3.67

the lowest prices were:
sam's club: 3.22
quick trip: 3.24
valero : 3.29

i never fill up w/o using this app...the prices are usually cheaper by my job...