Dan One reason could be because oil companies don't really want you to know about it. Most people don't have a clue what "octane" is. People don't care. Hard to give a simple and definitive answer. Anyway, why are there different grades of gas? Do you really believe that higher octane is somehow better? It is different, that's all. Because there are different cars out there with different engines and different grades are available for them. Not better, just different. Tom Niemczewski vin 6149 (in Poland!) tomciodmc@xxxxxxxxxxxxxx www.deloreana.com ----- Original Message ----- >> One of the reasons for your failed emissions might be the prolonged > use of >> premium fuel. I am assuming that you mean 93 octane. Higher octane gas >> causes deposits to form inside the cylinders and in the exhaust > system. That >> in turn will over time cause the compression to be raised. With that > you >> will get higher temperatures in the center of the cylinders along with >> unburned gasoline close to the edges of the cylinders. > > How come I've never heard of this? Granted, I'm not a mechanic nor an > engineer, but I'd think is this were true enough to cause problems > this knowledge would be more common than it is. To address comments privately to the moderating team, please address: moderators@xxxxxxxxxxx For more info on the list, tech articles, cars for sale see www.dmcnews.com To search the archives or view files, log in at http://groups.yahoo.com/group/dmcnews Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/dmcnews/ <*> To unsubscribe from this group, send an email to: dmcnews-unsubscribe@xxxxxxxxxxxxxxx <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/