DHS

This is a companion post to the one I started relating to carbon build-up. My tech told me that the winter blend we get here in Maine gets a high % of corn/ethanol and that does not burn as cleanly as the summer blend. Hence, carbon buildup.
I began using Mobil premium (92) when I got my '09 S5 last year. I got a great deal on gas rebate (15 cents pg). When that went away I went looking for new gas. The only 93 octane in Maine is Citgo so I started with that. Now that I am getting some carbon in the cylinders, I am wondering if I should go back too Mobil or Shell even though it has less octane and costs more. Or keep using the Citgo 93 and use a fuel additive more frequently.
Ix

lmariorod

The wife and I swear by Shell's V-Power. Here is a video. Made in the UK, but still very U.S. relevant.

Shell is V-Power here and Optimax in Europe. BP is Invigorate here and Ultimate in the UK. Supermarket here could be Costco, Sam's club, BJ's or hundreds of others.

DHS

Very interesting. I think that I will give the Shell a go and use the Audi additive from time to time. Hopefully that will postpone the inevitable. I appreciate your efforts on this and my other post.

ChipB

DHS - you mention Top Tier in the subject of your post, so you know that Audi recommends use of Top Tier fuel suppliers only, as these have higher levels of detergents than non-Top Tier. These detergents can help keep fuel injectors clean, but this has nothing to do with the problem of carbon buldup on the backside of the intake valves. The gas you use has nothing to do with that issue at all, because the back of the intake valves in Audi's DFI engine never comes in contact with gasoline. So if you're wondering how the choice of gas and/or additives can help mitigate carbon buildup on the valves - it can't.

Unless your engine is specifically tuned for 93 octane gas there is no advantage to using it over 91 octane. Just stick to Top Tier brands, and use 91 octane to save money.

banksc

Said recommendation (wanted to check for myself ):

http://www.audiusa.com/content/dam/a...l-Brochure.pdf

DHS

ChipB, I am obliged for your reply. I did assume that gas would affect the carbon issue, just as you noted. Actually, the 93 from Citgo is about 10 cents cheaper than the 91 from Shell or Mobil. Just yesterday I saw for the first time a placard on the Citgo fuel pump hose indicating that there is some new detergent additive in their gas. I will switch to Shell and use an additive every few tanks just to see if there is a difference.
Cheers.

DHS

Obliged.