Quest for better fuel economy

That is weird because I believe both cars have the same exact fuel tank.

I don't see rear axle beam bushings on your list. A 4 wheel alignment afterwards might help too.

IndigoBlueWagon said:

For a manual transmission car that FE is pretty low. I can count on my thumbs the number of tanks where I've gotten less than 40 MPG in my '02 Wagon. (...) Nevertheless, you should see at least 40 MPG in the worst conditions.

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Not to contradict you as you've provided a wealth of knowledge to this forum over the years and provide quality parts at excellent prices, but...

Every car is different with FE. I've gone down every single avenue to determine why my FE is what it is and there has been no clear mechanical indicator. "Worst" conditions for me would be short commuting in sub-0F temperatures... which yields 34-36 MPG consistently. This same commuting will get me right around 40 MPG in the warm months. All highway trips get me 50 MPG or more easily, regardless of temp. I need at least half a tank of all highway driving to hit mid-40s.

The point being: don't kill yourself seeking the holy grail of MPGs.

Don't disagree with you at all. Very low temp short trip driving can yield very low FE numbers. But the OP is in New Mexico, so I don't think he's seeing much sub-0 weather, unless he's at very high altitudes.

However, I commuted to Boston from the suburbs in my wagon for 4 years or so after purchase. My 35 mile one way commute could take 90 minutes to cover, sometimes longer. I'd still see 42-44 MPG winter, and 2-4 MPG more in summer. I've owned TDIs that didn't get great FE (my '97 A3 was one of them), but none of the 10 or so I've owned have consistently delivered less than 40 MPG. The OP is far enough off that curve that there's got to be something, or, more likely, multiple things, that can be improved in his car to help raise the MPG numbers.

mrfiat said:

That is weird because I believe both cars have the same exact fuel tank.

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What is there, some sort of baffle in there causing the difference, or the air vent is positioned higher on a wagon?

if it's really the exact same tank then it makes no sense that the capacity seems to change depending on the shape of the car it's bolted into.

It doesn't make sense, but people with sedans also tell me they get about a gallon less in the sedan than the wagon. I'm not the only one who can fill with up to 17 gallons in the wagon.

Only thing I can guess is that the filler neck is different, and may allow the vent to let more air out so the expansion tank fills more in the wagon.