Car: 1992, Pontiac Grand Am, 3300cc, auto, mileage 170k.
Driving environment = Houston traffic, Hot, wet, & sticky. ~48 gallons of gas used. ~1100 miles driven
I changed oil about a month ago from ordinary oil to a semi-synthetic blend. I don't remember what kind. Cost about $2.50 quart vs. $0.95 for regular oil. My gas mileage has gone from avg 21.8 mpg to 23.8 mpg. I have run
4 tanks of gas through my car so far. The increase was noticed for each tank. Nothing else in my driving, car, or environment has changed therefore the 2 mpg better mileage is probably from the semi-syn oil. Power seems to be about the same. Engine temp the same, etc.Based on the old mpg I would have used 50 gallons of gas instead of
48 gallons. The semi oil increases my driving expense by ~$1 per month if I change oil at 4k miles.