I have a 05 F150 and I get around 12mpg.. I'm trying to figure out how much better gas mileage I need a diesel to get to be worthy.

does the diesel need to get 15 to cover that 30-40 cent difference or do I need 20mpg?

 

15 will cover it, but don't forget the higher maintenance costs.

 

is that an assumption? I want to see the math

 

12 mpg x 30 gal = 360 miles
30 gal x $3.50 = $105
360 miles/ $105 = 3.42 miles/ dollar

15 mpg x 30 gal = 450 miles
30 gal x $3.85 = $115.5
450 miles/ $115.5 = 3.90 miles / dollar

But then let's look at $100 oil changes, frequent fuel filter changes, take-out-a-second-mortgage repair costs, losing a minimum of $3k trading vehicles in, etc. . . .

Keep your truck.

 

12mpg? Sounds like the fix for you is right foot related. Granted I have the 4.6, but I also have a 4x4 with 33's, and 4.56 gears, and I average about 15-16 highway. Even towing my boat, I get better than 12.