Interesting. I thought cars loose gas millage as the get older.
I thought so too. But I typically buy 4-5 year old cars and keep them for 10-11 years. I don't keep them so long that they end up being oil burners and candidates for new engines. Up to about 220,000km. I have never seen a dropoff in mileage while I've owned them. Our 1990 Dodge Spirit is still capable of 42mpg on the highway, as it has been since we bought it with 80,000km. It has twice the mileage now.
Brand new cars are reputed to get better mileage after the engines are broken in. I read all sorts of theories about which makers supply tighter engines etc, but I've never heard of a study to back up these claims. And if it was true of our vehicle that we bought new, the effect was too small to be apparent.
There is also a theory that as cars age, the bearings, engine parts etc. wear and loosen up. The cars become less "tight", but may roll with less resistance. Obviously when they get to oil burning condition, the engines probably will be losing performance and therefore efficiency as there's more compressin/blowby losses.
