$4k for an engine.
$1k+ to swap?
10mpg to 20mpg.
10,000miles
1000gal gas x$2.80= $2800
500 gal dsl x $3.40 = $1700
So, you might recover $1100 per 10k miles.
40 or 50k miles to break even. Bet you won't drive that in
decades if it's a barn dweller. Plus, if it now get 12 or 14 mpg,
your payoff just got worse.
I love the torque and performance of a Cummins12v, many
who are used to gas engines don't like the turbo lag, and
high torque/low horsepower profile.
Always hearing how Chevy or Ford diesels are better, just
because they are more like what car drivers are used to.
