acarney

So in July right after I bought the car I was getting max 19.5 or so MPG when driving very soft and a mix of freeway and city driving WITH the AC on. I was pretty happy because hey, it's a big heavy car and stuff. When I floored it for a full tank of every light that did go down a bit, maybe 17.9 or even a little less, but never too terrible. Now when I'm driving the last couple tanks I've been getting 17.4 or 17.5 mpg no matter HOW I drive! I drove as soft as ever and never floored it and I did 17.4 mpg across a full tank and now I'm 3/4 tank after I've been flooring it off each light and driving it like I stole it and I'm estimating I'll get about 17 to 17.5 mpg.

The only things changed that I can figure is that the temp has gone from 80 to 100 degrees outside to 20 to 40 degrees outside and I'm using the heat. Could the cold temps be killing some of my mpg because of the oil staying thicker or something? I'm running 5w30. Should I switch to 0w40?

I've also had some service done on it. Air filter and cabin air filter was replaced and timing belt and water pump and thermostat and Blauparts valve cover gasket kit (valve cover, cam tensioner gasket, cam shaft valley seals, viton front/rear camshaft seals). Could any of that stuff being installed wrong cause such a drop in mpg? When he was replacing some of the seals he did say that it looked like one had been replaced before and installed using a cheap or wrong silicon grease so he took extra time to clean it all out. I thought one of those seals was suppose to be installed completely dry without any kind of grease, I'm not sure if it was the one he was talking about or not and he does seem to know what he's doing (replaced my torque converter at the end of July and did a great job and only works on BMW/Audi). I was going to have my fuel filter replaced but we pushed that off until my next oil change (coming up very soon) because he ran out of time. Could a dirty fuel filter make that big of a difference and so fast? Right before going into the shop I was fine with MPG; I can't tell if it was right after that I had this drop because I would hang around in the car waiting for my girlfriend for awhile a couple times a week so that gave me a lower mpg rating across the full tank anyway.

Can anyone else think of anything that could cause this kind of issue? Any way my Audi stealership or independent guy could check to see if things are normal? I'm pretty broke now so I can't spend a lot with it being in the shop with them just poking around or running tests but I do have an extended warranty I could try to use again if they can figure out what's wrong fairly fast and cheaply. It's driving me insane that having no fun at all and driving like an old person is still only getting me about 320 miles on a full tank!

4Driver4

Winter mix gas. Milage will rise again the spring.

thejulex

That would do it. My mileage is down as well, but I was attributing it to getting K04s and all the surrounding hardware/software and not being able to just cruise anymore

acarney

Never even thought to think it could be the mix of fuel! I always use the same grade and the same two fuel stations so I didn't even think it could be something on that end! Still seems a little funny that when I drive like I stole it compared to when I drive normal and easy there's only a half a mpg to one mpg difference, but maybe I'll try to forget about it until spring rolls around and see if my easy relaxed driving jumps back up to 19mpg - ish.

VONBOTTLE

most of my driving is putzing around town and i average around 16 mpg in warmer months and closer to 14 mpg in winter

Just Me

also, as weather gets colder, cold enrichment ( aka e-choke) dumps fuel into the engine until it warms up.

G

4N 4RING

You are very low, something is not right. I drive nicely, cruise control 65 mph, commuting 35 miles one way (70% highway). However, I floor it on ramps. Calculated: I zero the trip odometer when I re-fill and I divide gas filled by miles driven. The display is always 2 mpg optimistic. Car is 165kmi 2.7tq and I use 93 octane and wheels are stock. If your wheels are larger, the odometer reads less miles, therefore it calculates lower mpg.

4N 4RING

...so this might be the difference.

Just Me

for the record -

My S6 avant gets 16-17 in mixed driving.
My 95 a6q (2.8, auto) gets 19-20 in mixed driving.
My 2000 S4 6-spM (now gone) got 21-22 in mixed driving.

So your mileage doesn't sound so horrible, and the 10% change can be attributed to winter gax mix plus richer running, IMO.

counter-intuitively, i dont find that the mileage is greatly affected by "hard" driving. Sometimes light throttle make sit worse. (actually, engineering theory supports me, but its a LONG story)

G

DWC_2.7T

Not enough information. Do you keep track of your average speed reading? A little more traffic, a little lower average speed plus winter blend gas can easily drop you 1-2 mpg. Or low tire pressure. I've consistently averaged 17.4 to 17.6 commuting in my 2.7T for years, but mine is all city streets @ 25 mph average.