We seem to be covering the 2010 Volkswagen Golf TDI clean diesel hatchback an awful lot here, but a recent blog post raised an issue we hadn't considered: How far can the 2010 Golf TDI go on a single tankful of diesel fuel?

The question comes from blogger, host of #carchat on Twitter, and general all-around car personality Michael Banovsky.

In reviewing the new 2010 Golf TDI for Canadian and U.S. outlets, he stumbled when calculating maximum range, because the two countries' fuel economy rankings differ. A lot.

2010 Volkswagen Golf TDI

2010 Volkswagen Golf TDI

2010 Volkswagen Golf TDI

2010 Volkswagen Golf TDI

2010 Volkswagen Golf TDI

2010 Volkswagen Golf TDI

2010 Volkswagen Golf TDI

2010 Volkswagen Golf TDI

Does Canadian diesel go further?

After doing the math to match gallons and liters, and fuel consumption (liters per 100 kilometers)  with gas mileage (miles per gallon), he found that Canadian ratings put the maximum range at 740 miles (1195 kilometers), while the U.S. figures provide for only 610 miles (980 km).

Digging in, he found that U.S. and Canadian fuel economy figures differed only for diesels. The EPA says the 2010 Golf TDI gets 30 mpg city / 42 mpg highway, while the Canadian ratings convert to 35 mpg city / 50 mpg highway.

The numbers for gasoline-engined Golfs, however, were close to identical: 22 mpg city / 30 mpg highway in the U.S., 22 mpg city / 33 mpg highway in Canada.

U.S. the odd man out

And U.S. ratings are the outliers here; Canadian figures were close to European ratings, despite differences in emissions control equpment.

As we all expected, the explanation lies with "the gummint". Volkswagen Canada explains that the U.S. Environmental Protection Agency's testing regimens and calculation rules differ from those at its Canadian counterpart.

Chronic underrating

This is a chronic problem for diesel owners and buyers: The EPA ratings aren't as good as the TDI's actual mileage.

We've noted before that many reports show the Volkswagen Jetta TDI--which uses the same 2.0-liter diesel as the Golf TDI--gives far better real-world mileage than its ratings indicate.

How far? Ask your bladder

As the old saying goes, your mileage may vary. But in this case, here's our response to the opening inquiry:

Question: How far can the 2010 VW Golf TDI go on a tank of diesel fuel?

Answer: Between 600 and 750 miles and, most likely, far longer than your bladder will hold out.

Reviews: TDI is big winner

We think the 2010 Volkswagen Golf TDI  will be the big clean diesel winner in the U.S. market, and that's before we've even driven one.

Our colleague Bengt Halvorson gave a big thumbs-up after his drive in a European version of the 2010 Golf TDI, and Marty Padgett offered mostly similar praise in his drive report of the Golf TDI. That car is just now going on sale, at a base price of $21,990 for the two-door hatchback.

We just wish the EPA could get its clean-diesel fuel economy figures to reflect the real world a little better.

[Michael Banovsky]