Mileage thought experiment

[Biodiesel300TD]

A lot of folks I talk to complain about how mileage of modern vehicles hasn't increased. I tell them it has but the weight of the vehicles we drive now it much more than it used to be, negating the mileage increase. A 1982 VW Jetta weighs 1800lbs. A 2004 Jetta weighs 3000lbs. Yet the mileage has remained about the same about 40mpg. So acheivements had to have been made in mileage to keep a car that weighs nearly twice as much as it used to to maintain the same mileage. So what should happen if I were to plop the TDI engine out of my 2004 Jetta into an '82 Jetta? I presume the mileage would go up. I wonder how much. Granted, I wouldn't want to get into a wreck on the highway in an 82 Jetta. But maybe my savings in fuel costs would pay for the hospital bills.

[rscurtis]

I've been saying that for years. New vehicles are seriously over-contented, and many are over powered- that's where some of your FE improvements went. We now have the 300 HP "mini" van, the 403 HP half ton PU, the 556 HP Cadillac and all the new HD pickups are sporting 350-400 HP and 800 ft./lb. of torque.

I had an '89 Jetta diesel that would do mid fifties on the highway during the 55 MPH era. As you said, that car with a modern TDI engine would be more economical, and go like a rocket as a bonus.

For all the talk about reducing oil imports and the concern about MMGW (I'm not a believer in this) we as a society don't seem too concerned about looking for real solutions.

[LandYaghtLover]

Well my 91 Benz is just 100 pound LESS than the 1996 Mark VIII I had.

Mark VIII highway: 28-30mpg (4.6 liter V8)

560 SEL highway: 17-18mpg (5.6 liter V8)

Maybe not the best comparison since they are not the same lines of cars. But it does show that engine technology has improved and if done right a heavy car can be somewhat economical.

[charmalu]

"So what should happen if I were to plop the TDI engine out of my 2004 Jetta into an '82 Jetta?"

Your wife would kill you and you wouldn`t have to worry about the hospital bills.

You bring up a good point. the efficiency of the emissions and fuel is better than the 82, horse ower probably gone up some, but as you said the weight of the vehicle has also gone up. and that is probably the safety features of the newer cars.

Charlie

[Orv]

Originally Posted by Biodiesel300TD

A lot of folks I talk to complain about how mileage of modern vehicles hasn't increased. I tell them it has but the weight of the vehicles we drive now it much more than it used to be, negating the mileage increase. A 1982 VW Jetta weighs 1800lbs. A 2004 Jetta weighs 3000lbs. Yet the mileage has remained about the same about 40mpg.

I don't know if "about the same" is really that correct, except that we tend to round off to the nearest multiple of ten.

According to fueleconomy.gov an '84 Jetta (they don't go back to '82) with a diesel and a 5-speed got 37 mpg highway. An '04 Jetta got 42 highway. That's a 14% improvement; at $4/gallon it's like getting $0.56 off every gallon of diesel you put into it.

Also keep in mind there's been model creep. An '04 Jetta is a significantly larger car than an '82 in pretty much every dimension. The '82 was decidedly a compact and the '04 is pushing into midsize territory. If you compare the '82 to a modern car with the same dimensions I think you'll see a pretty dramatic difference.

[iwrock]

This would happen:

http://green.autoblog.com/2009/09/03/1990-mercedes-190-d-upgraded-to-new-blueefficiency-engine-jumps/

The 190D originally achieved 32MPG, and managed 48MPG with the new engine.

[engatwork]

Pretty cool what they did with the 190.

I have read that the E220 diesel that is sold in Europe gets over 40 mpg.

[rscurtis]

Orv, I don't buy that 37 MPG figure. My '89 consistently got 42 in local driving and the mid fifties on the road.

[martureo]

You might also have to factor in the EPA effects on vehicles in the last three decades.

This is especially true for heavy duty truck engines. I worked at a powertrain plant designing the 13 & 15 liter engines and the mileage figures were a little absurd.

e.g. EPA 2007 engines (engines were sometimes referred to by the emissions requirement year they met) got around 7.25mpg. EPA 2010 engines had much stricter particulate filter requirements and got 8.50 mpg. But the newer engines in 2010 we shipped to other countries got around 9.5 mpg.

Simply put the engines get more efficient but the observed net increase mpg is lower than it would normally be because of the emissions requirements (egr valves/particulate filters/soot combustion chambers). One wouldn't be able to accurately compare the mpg differences in engines/vehicles decades apart without removing emissions controls or bringing the old engine/vehicle up to the emissions standard.


On a related note, go google 'Project Sipster'. I think Top Gear magazine did it. They ended up putting a modern TDI into an old rabbit.

[jonbobshinigin]

iwrock - I was just about to post that link...good call!

As for the overpowered cars...we are talking leisure/practical vehicles vs performance vehicles. Personally, I am looking to get 300HP from my wagon one day...while retaining decent fuel economy if possible.