Lol $20 saving per week on fuel, eventually would cost him $5000 plus in repairs if he stayed on there. Work it out $1040 saving per year plus Repair costs if something major goes rong, ahhh all i say is you will not save money, and if you did well you just spent it plus alot more ontop to fix anything, which assuming from the previous posts will happen alot sooner than you hope it would.
Good tip would be Drive it better, and the good old "Your fuel economy is determined BY your RIGHT FOOT"
Cheers A