I have an '07 GT/CS 5 speed manual and recently my MPG has dropped from around 18+ MPG around town to about 15 - 16 MPG. Any ideas? I have about 46,000 miles with a K&N Drop in filter, synthentic oil changes every 5k miles. The only thing i can possibly think is that I have never changed the fuel filter not sure if that would do it o not.

 

Sounds like the kind of drop I see when the oil companies have to switch to a winter formula or when using gas with ethanol.

=Vic=

 

I'd say the same thing about the seasonal fuel formulations... but 46k miles and still running the stock fuel filter?! Yikes, change that thing, it's pretty quick and about $25 for the Ford filter. Just my $0.02.

 

I would assume that a clogged fuel filter would decrease performance, but increase gas mileage.
The filter change s/b done at 30K mi. though.

 

I'm not taking any bets as to whether the old fuel filter is the MPG culprit, just that I've seen some shamefully dirty fuel filters with only 25k miles on them.

There are a lot of different factors that could contribute to gas mileage changes though. Does it still run the same now as it did before?

 

18 mpg? Wow that's great, I typically average 14 mpg but then again I can't get out of 3rd gear cause it's just so much fun!

 

Yeah the car runs same as day 1 just the drop in MPG. ion this tank I even tried to baby it (no high RPM shift changes) and now it is around 15mpg. I have tried Lucas fuel injector cleaner and a tank of 89 octane at the same time - as I usually run 87. I will try the fuel filter change to see if that does anything to help out. If not what else should I be looking at?

 

You haven't mentioned the last time you cleaned the air filter.
An air filter can clog in 1 day in dusty areas.
That can kill MPGs easily.

 

I'm experiencing the same thing and I did change my fuel filter at 30k, and clean the air filter (also K&N) every 6 months

 

+1 on the summer blend. I have seen my MPG change that much when running on Arizona gas vs California gas. FYI, it goes down in California.

 

So i changed the fuel filter (it was clogged) also cleaned the K&N and seems like I back closer to 18mpg. Amazing what a little maintence can do!!! Thanks