Drop in MPG

[ralvarad]

So I've had my 03 Cayenne S since January (bought used with 30K miles). When I first got it the gas mileage was about 14.7...it's at 12.7 mpg now. I'm not sure what the problem is. The service manager tells me there's nothing wrong with it but I'm skeptical.

A few more tid bits of information:

-The average speed has gone from 32 to 26 mph. (But I think this is due to city driving because I do drive aggressively/fast)

-I recently had to replace the spark plugs and engine coils (one of the plugs was misfiring, service tells me there might be carbon build up)

-I haven't changed the gas I put in. I use BP 93 ALWAYS.

-I have added Lucas Oil Fuel Injector cleaner several times (about every three months)

-Had a rear end collision (not my fault) where my left tailpipe was bent, but fixed (unbent)

-Don't know how to change the air filter (LOL)

Can anyone offer any words of advice?

Most certainly would appreciate it. Thanks!

[ralvarad]

PS. It stayed in the 14 range for a while (until May or so), then all of a sudden this summer it dropped to 13.6. Then it just kept going down 0.1 mpg every week or so.

-The tires have been rotated and there is some wear, but good tread. (Balanced and aligned)

[JeTexas]

There's so many variables, not the least of which is your driving style and the traffic where you're driving. As you got more comfortable with the car, you may have started putting your foot down harder and more often without even realizing it. Traffic in the area you drive might have gotten slower and more congested. Maybe it is time to change the air filter. Who knows?

[mudman2]

Never use injector cleaner there is no need, its only got 30K miles, maybe at 230K miles

Air filters are not normally due yet but you can take them out and look at them, see my gallery on rennlist for instructions

Heavy pedal will do it, but tire pressures are my bet, check them soon

There's so many variables, not the least of which is your driving style and the traffic where you're driving. As you got more comfortable with the car, you may have started putting your foot down harder and more often without even realizing it. Traffic in the area you drive might have gotten slower and more congested. Maybe it is time to change the air filter. Who knows?

[secretagent214]

As mudman says, tire pressure can do it...low tire pressure = poorer gas mileage. As it gets colder out, tire pressure will drop even without a leak. Or maybe that change in average speed may imply that you have more stops and starts...more starts = poorer gas mileage. Or maybe it has to do with your air conditioner usage...AC usage can reduce fuel efficiency by up to 20%. That would explain the sudden drop in late spring, around the time it starts warming up in Pittsburg. It's hard to say with the endless possible variables and without any other symptoms of anything.

Edited December 16, 2008 by secretagent214