Confused about fuel mileage

I’m very confused about fuel mileage and while it seems a simple concept, things don’t seem to add up. Here are some examples:

1. I drive a 2002 Saturn S-series sedan with a 5-speed. I get an honest 34-36 miles per gallon around town and a consistent 44 mpg on the interstate at 70 mph. The car was advertised as 29 mpg/40 mpg when I bought it, but someone told me they’ve changed the way they calculate mpg since then. Ok.

2. My Saturn is getting up there: 216k miles and climbing. Eventually I’ll need a new car. Why is it that in this era of high fuel costs I’m going to have to buy a hybrid or a diesel to get comparable fuel mileage now, 11 years after they built my Saturn? Did they forget how to build gasoline powered cars that get good mileage?

3. I watched an episode of the British car show Top Gear recently; they raced from Switzerland to England, 750 miles, on one tank of fuel. The VW got 75 mpg, the Subaru got really good mileage and the Jaguar V6 twin turbo averaged almost 60 mpg – and the guy driving it was deliberately driving uneconomically (70-80 mph, A/C on, etc.) When I go to the Jaguar or Subaru websites I don’t see anything like this. What the heck is going on and why can’t my wife’s Buick V6 get 60 mpg?

4. I was just on Chevy’s website; the new $40k Volt gets 'way less than 40 mpg, once you’ve gone past the 35 mile electric range. This thing, at $40k, is not as efficient as my Saturn! GM has no fuel efficient cars. Have they forgotten how to make them, lost interest, spend their bailout money on oil company shares or what? It’s driving me nuts. Anyone know any answers?


  1. The change was to better represent real world driving. You’re simply getting great mileage.

  2. lots of people are wondering this. There is no real answer except that engines are getting more powerful.

  3. A British (imperial) gallon contains four imperial quarts of 40 ounce each for a total of 160 ounces, and a US gallon contains four US quarts of 32 ounces each, for a total of 128 ounces.

  4. GM never could make fuel efficient cars that were any good. I had a brand new '72 Vega. And over these last decades they’ve tried to use cheapo “rebadged” cars from other manufacturers to compensate. 'Nuff said.

If you were watching the British version of the show you were getting numbers in KILOMETERS…not miles. They may have said mileage as a coverall term…but what they should have said was KILOMETERS. NO TWIN TURBO JAG will get 60 MILES per gallon. All the data you heard was most definitely in Km. Hope this helps

It’s sad that GM could screw up even with a good vehicle line like the Saturn. I have a gearhead friend (and frugal/cheapskate) who buys 10-year-old Saturn sedans for $1000 and has great success with them. He loves the fact that they have timing chains instead of belts, and he gets around 40 mpg on the highway.

So, yeah, you’re not the only one who’s confused…

" A British (imperial) gallon contains four imperial quarts of 40 ounce each for a total of 160 ounces, and a US gallon contains four US quarts of 32 ounces each, for a total of 128 ounces. "

That’s true, but that’s not enough difference to account for it. An extra quart per gal. or 25% increase. Figuring the mileage depicted at 75% it would still equal 56 mpg & 45 mpg respectively.

Now that makes sense.

Also, that Top Gear was with diesels, few of which are available here (VW). Nobody should buy a Volt if they’re just going to drive around on the gas engine. The great mpgs come from charging it up each night, so this is an unfair comparison. As for other options, check out the Cruze with the base engine and 5 speed, a Honda Fit, etc. The EPA web site has lots of info on all available cars.

Nope, it was mpgs, just with diesels.

Since '02 most mfgr’s have focused more on performance and not really done that much to increase mpg. If you watch the car commercials they still sell spinning tires, and zooming around a guy sitting in the desert, etc.

Cars got bigger, faster, and more powerful in general and mpg hasn’t increased much in general. This is changing now, but for the last 10 years it was all about acceleration and power over mpg.

If you take my theory further you will find that the numbers they gave you in KILOMETERS…factored/converted to MILES…the “mileage” numbers they gave would sound more plausable to your ears in Good Ole Merican MILEAGE for the specified cars.

Correct me if I’m wrong…but when the Brits went metric, they kept miles for distance, and stones (?!) for weight…for whatever reasons. This would make miles per (Imperial) gallon the likely measurement.

Yep, any time km are involved, it’s reported as liters/100 km, I think (consumption), not km/imperial gallon.

Fun fact - the difference between the Imperial and US gallon goes back to the gallon used by beer makers (ale gallon) vs. the gallon used by wine makers (wine gallon). Go figger…

I know. It’s only a part of the picture. The other parts have been mentioned by the others.

I didn’t see the show in question, so know no details.

to add my thoughts:

  1. Sweet. That really is excellent mileage, and shows that your car (well, engine anyway) is in great shape.

  2. No, they know how to build them. But people don’t want them. My TL is considered a “slow” sport sedan because it does 0-60 in 7 seconds. To put that in perspective, it’s only 0.7 seconds slower than the 1997 Porsche Carrera S, and only 0.3 seconds slower than a Lamborghini Miura, and yet it’s considered slow for a sedan. People want to drive race cars, basically, and so while engines are getting more efficient, they’re also getting insanely overpowered so that they can turn in performance numbers that were formerly the exclusive domain of exotic supercars.

I’ve often thought the same as you - I had a CRX HF awhile back that got 50mpg out of a regular engine. The new Insight has an exotic hybrid engine setup, and all sorts of compromises as far as comfort, etc, and gets about the same mileage. Only when the CRX’s battery died, I’d go to the parts store and pick up a new one for $50 bucks. Try doing that with the Insight’s battery pack.

  1. In addition to TSM’s explanation, I remember that episode myself. I may be wrong, but I believe that was a diesel Jag. You can get all sorts of cars with diesel engines in Europe that you can’t get here - another annoying thing about the car scene in the States.

  2. The Volt was a marketing ploy. It was never intended to be a real solution to anything and in fact it wouldn’t surprise me if GM is hoping that it’s a dismal failure so they can put off having to figure out how to power a car without gasoline for a few more years.

Lots of good points Shadow.

I’ve come to wonder of the Volt isn’t just being still pursued to please the feds. I wouldn’t be surprised if it failed. Other manufacturers are starting to come out with true EVs now as well as other options better than the Volt.

The top Gear episode featured diesel cars and their gallon uses 4.5 liters per gallon where the US uses 3.8 liters per gallon.
I also remember the episode, but can’t seem to find it on

As I remenber the change the EPA make in mpg calculations should result in a number that better reflects what the car actually gets. This means the number should go lower not higher like you have accepted. The main question that I believe you are trying to ask is “why did/does a car made “years ago” get more mpg than a car made today”? The answer probably involves the fact that ever increasing mpg figures were something the manufactures did not attach a priority to. Find out (or make a educated conclusion) what parameters the manufactures did priortize and you will have your answer.

The Jag was a diesel.

They were getting kilometers per gallon.

UPDATE: I just now was reminded (see below) that petrol is sold by the liter in the UK. I should not have commented but the high fuel economy numbers seem to be false.

If your Saturn is an SL-1, A friend of mine had one of those and it ran about 2500 RPM @ 70 MPH. Pretty long legs for a small 4 cylinder. That would likely be a large part of why you get such good mileage. As for the Jag getting 60 MPG at 80 MPH with the a/c on, I don’t know what system of measurement they were using, but in american miles per american gallon, NO WAY!