The cost of saving

Jeep is introducing a diesel for the Grand Cherokee this year.  It gets roughly 4mpg better than the V6 (21/28 vs 17/24).  The cost of fuels today is $3.50 for unleaded, and $4.00 for diesel.  If you drive 10,000 miles a year, all at highway MPG, you'd use 357 gallons of diesel, or 417 of unleaded.  Multiplying that out, it would cost you $1428 for the diesel and $1460 for the unleaded, a savings of $32.  Plus, you have to add urea every 10,000 miles to the diesel vehicle, which more than likely cost more than $32.  The cost of the diesel is $2300 over the V8, which itself is $2200 more than the V6 this year, for a total premium of $4500.  It'd take 140 years to make up that cost (without including the urea), although you'd get some of it back when you got rid of the vehicle.