TDI fuel economy

I have a 2010 A3 TDI that is getting much lower fuel economy than I would have expected. I have always been able to get well above EPA estimates in all my previous vehicles and, what with the VW TDI wars, it seemed likely that this motor would perform similarly to the new Golf TDI. However, I have been getting much lower than EPA estimates but the dealer can’t find anything wrong with the car. I can’t say I trust my dealer as the mechanic did ask me what octane I’ve been putting in the car…! Has anyone else had this problem with the new TDI? Any ideas what can be wrong with it? It has about 15,000 miles on it so it SHOULD be past break-in and starting to improve, right? Do they have winter diesel like they have winter gas because I recently saw a significant DROP in economy from the already lower-than-expected level? The only thing I DO know for sure from the dealer is that the computer DOES have the latest software.

What kind of mileage is your car currently getting exactly and what method are you using to determine your fuel mileage?

What are your numbers and their estimates ? Later EPA estimates are more realistic and based more upon real life driving situations than before. They will be harder achieve, especially if your driving habits are not near perfect.

The EPA estimate for highway (which constitutes 95% of my driving) is 42. The absolute highest I ever got in this car was actually while navigating the little coastal towns of Nova Scotia - about 46 mpg. Typically, I will get about 40 and the last two tanks have been roughly 38.

I just do a simple divide miles by gallons which I know is not completely accurate but my last car - a little Honda - was consistent (with the same exact commute) to within 1 mpg with this method.

I guess what concerns me the most is that everyone always raves about the huge jump in fuel economy they see when the motor breaks in… but the economy has been decreasing slowly since I got the car!

What’s more accurate than dividing miles driven by gallon burned?

You once beat the EPA highway estimate by 4 mpg, and are consistently within 2-4 mpg of the EPA estimate. I don’t see big a problem.

Remember the EPA number is an ESTIMATE. They test the car indoors, on a dynamometer, under highly controlled conditions. It’s not a real world number.

Winter mileage is always lower than summer mileage. Wait until spring. It may improve.

Hate to break it to you, but if you’re getting 38-40 MPG overall, you’re getting exactly the kind of mileage you’re supposed to be getting. The EPA estimates for this car are 30 MPG city and 42 MPG highway. Your car is getting the kind of mileage it’s expected to. Perhaps your expectations were a bit overly optimistic.

I guess it is just disappointment that this vehicle’s EPA estimate is so close to what I am getting - I am used to getting SIGNIFICANTLY better than the estimates… my last car was estimated at 30/33 and I never got below 42 but usually did about 46 in it. With the estimate at 42 plus people’s ravings about how much better they could do with the diesels, I was expecting something more like 50.

I just want to be sure that there is not something wrong with the injectors - this is such a complex engine and to have the DEALER ask what octane fuel I was using in my DIESEL got me really thinking that they might do more damage than good just by looking at it. If others out there are getting the same fuel economy, cool… but if everyone else is getting what I expected to, I think I’ll have to find someone else to take it to.

As mentioned the EPA tests is done under controlled conditions to insure consistant results among the different car and motors tested. The new testing process is more realistice than the old one. The old test used 55 mph as the test speed (due to the 55 mph speed limit at the time the test was instituted). They upped the highway speed in the new test, likely to 65 mph.

It your highway speed is normally 70 mph or more you would get lower actual highway mileage than the EPA test. How much starting and stopping you do, and how hard you accelerate also affect your actual mileage and likely deviate from the EPA test. Finally, as someone noted you are driving in a cold climate and that cuts the actual mileage down a bit as well.

Even with the diesel the A3 is a “sporty” oriented car and it is likely some of the fun of driving it can impact on the mpg. If you want max mpg. Make sure your tires are at the recommended pressure or even 1 or 2 lbs above it. Drive like a little ol lady. Don’t idle the motor to get or keep the cabin warm. Don’t exceed 65 mph on the highway. Unless a semi is bearing down on you on the “on ramp” take about 2 miles to reach cruising speed on the highway.

You can get the 42 mpg on an interstate highway trip as long as you don’t mix in any city driving at all. Get fuel when you can on the interstate and again when you get off and you’ll get your 42.

Winter mileage is always lower than summer mileage. Wait until spring. It may improve.
Great point…winter driving esp in so called high mileage cars, diesel or not, can vary dramatically with the temp. Warm up times, esp. with a diesel, are critical. The are one of the few motors, it actually may make sense to idle them for a while if you do a lot of stop and go. I agree with everyone…live with it till spring and use only highly regulated long trip mileage to make comparisons to eliminate as many factors as possible.
I’d trade your mileage now anytime…meet you in Calais for a swap. :=)

Yes, there is winter diesel fuel. #1 diesel is mixed with #2 to lower the jelling temp. #1 has less energy content per gallon than #2. #2 is what you get during the summer. I don’t know how this is handled in the extreme southern US where blending may not be needed.

I just do a simple divide miles by gallons which I know is not completely accurate

That is totally accurate, with just rounding errors. Of course averaging several tank fuels can eliminate the measurement errors.

You have two strikes against you right now.  It is new (my guess) and new cars need a few tank fills to break in the engine and then it will go up a little.  It will also go up when the temperature goes up and it will also go up when the winter fuels are replaced with the summer mix.  

 My 2002 TDI is getting about 45 in the city right now, which is about two mpg lower than summer. On the highway, I get a few miles per gallon better than winter. 

 You may want to stop by  the They are the place for everything TDI.

I believe back in 07 or 08 EPA started using a more realistic method of testing, which lowered many estimates on some older vehicles should they have used this new test.
And I’m pretty certain the mechanic isn’t familiar with diesels since he asked you what octane you were using. I do believe diesel uses Cetane ratings provides EPA estimates and actual mileage from users that post it. Tow posters drive 70% highway and get 40 to 41 MPG. It looks like you are about where you should be.

Look here to learn about how the EPA tests cars for mileage.

If you drive exactly the same way they do on the dynamometer and under the same conditions, you will get the same mileage. But the purpose if the ratings is to allow you to compare cars to each other before you buy them. You can be certain that you would get lower mileage with any other car you could purchase, too.