Well i traveled about 275 miles and pulled off 23 mpg.......

Some of it was city driving, about 20 miles or so......also it was with a constant speed of 80 mph.....

Just thought i would share....

305 TBI, 139,000 miles, stock except for K&N Open Element.......

 

That is pretty good but shouldn't you be getting slightly better for being mostly stock? I would imagine by the looks of your car that you have a fully maintananced car with good running ignition and feul. Therefore, you may want to data log and see if you are runing rich anywhere or to make sure everything is up to par.

 

This is true, it had a tune-up less then 3 months ago, with some new platinum spark plugs....

BUT, my engine has is going downhill, has a head gasket problem, so there is white smoke out of the exhaust when at idle, I would imagine this is the cause of my decreased gas mileage, I can't justify fixing it now, when it's getting a new 350 in about 2 months anyway......

 

Well if you are replacing it with a 350 don't worry about it. When I ran the platimun plus are ran really rich at idle and it gave me horrible mileage. You may have bad valve seals and not a head gasket problem.

 

Can having bad valve seals get you worse gas mileage, because mine are about shot (it burns oil pretty bad) and in town i have been getting just barely over 200 miles on a tank.