Hello all. Owner of a 2004 A6 3.0L, just about 78,000 miles and I have some recent fuel economy concerns. I've owned the car for less than a year now and have noticed a significant drop in MPG (according to the dash.) I know that this isn't the most reliable source so I'm currently in the process of calculating an actual MPG using a good old pencil and paper.

Anyway, I've been trying to be much more hands on and been doing small jobs myself. I recently changed the oil, oil filter, spark plugs, air filter, tires, alignment, had a set of new flex pipes welded in, and did the front motor mount (snub mount) myself. After all of this, I seem to have somehow lost some MGPs?!? Currently averaging 14MPG with local city driving when I remember getting at least 17-18MPG when I first purchased the car. Again this is based off the display on the dash, so accuracy is probably not spot on but I'd expect it to be close. According to the readings, when accelerating through 1st and 2nd gear, I'm getting a whopping 6MPG!!!! This just doesn't seem right. I'm no speed demon and have been trying to baby the car as much as possible.

Really hoping that I'm not stuck with this horrendous mileage and that I'm missing something to help improve my economy. I've had suggestions to take a look at the o2 sensors but am not sure where to begin with that or if that is even a feasible solution. Something about dumping more gas into the engine then I need due to a faulty sensor or some bad connection. No check engine lights though. Could purchasing a VAG-COM and getting some readings help? Not sure if no lights means no problems or if I could get some new info regardless of what the dash says.

Also after doing some reading and STF I've thought about cats causing some loss in efficiency (**fingers crossed** please don't be the cats, please don' t be the cats ). Might make sense considering I started to notice the drop in MPG after the new flex pipes were welded in. You can imagine my surprise when one fixes an exhaust system and gets a WORSE gas mileage! Ugh.

Apart from the gas stuff, would also like some opinions on timing belt/accessory belt. I'm getting a high pitched noise from that area (I know that there is a lot of stuff going on there) and am curios if anyone has any suggestions on where to look first/if its something I can attack myself.

Thanks in advance for the input.

 

Next time you fill up reset your trip odometer. When you fill up after that, take the number of miles you got from a tank of gas shown on the trip odometer and divide it by the number of gallons you just put in to fill up (shown on the gas pump). That's your average MPG for that tank of gas. Yes you will get 5 - 9 mpg while accelerating, that's normal. But once you get up to speed you can use the real time mpg to help you adjust your driving habits to improve milage. Also try some different octane gasolines and see if there is any change. When I do an oil change, I always add a can of Liqui-moly MoS2 Oil Treatment. Reduces friction, protects, etc.

 

You did not ask, but at 78k and 11 years you need to seriously consider the timing belt service. As far as mpg, my computer has been consistently 1.5-2 mpg higher than manually calculated mileage and I have 230k on the car. My 2.7T gets about 18-20 in mixed city-highway and 23-25 on the highway. My daughter's 2003 A4 3.0 MT6 is almost the same around town, but does 27-29 on the highway.

Make sure your tires are properly aired up. You lose a pound a month and it can vary quite a bit with temperature change.

 

Thanks for the input. I know that I am just about due for a timing belt service and don't have any records from the dealer to determine if it was done or not. My plan was to wait until mid-June to take care of the timing belt because I'm currently a school teacher. This way over the summer, I can go a couple days without needing the car and can attack the timing belt/water pump myself.

I took a look at it and it appears to be ok. No cracks or wearing from what I can tell. You think I can wait a month or two to get it done or should I take it to a shop?

Also coil packs seemed to solve some of my fuel economy issues. Had one go bad on me and replaced it. Seemed to improve MPG a decent amount. Need to get them all done soon. You can check out my other posts in the AudiWorld Fourm.

MPG and other stuff - AudiWorld Forums