so my motor is starting to knock. geeting worse but ill drive her till she blows. lol. so...

i have a 97 disco 1. 4.0 auto. i tow alot! and it is killing my motor. i regulary tow over 4500lbs. i need a diesel. i am looking at the 6.2 gm turbo. mercedes om617. or i would truly love to do a for 6.9 idi as they are cheap. great for towing. and last forever. however the max rpm on them is like 3500. any ideas. i need the lowest cost set-up that is good for towing. i do like the om617 as the max rpm is a little over 5k better for the auto tranny but idk how it would hold up for towing

 

i know the diesel idea has been thrown around alot. but not the ford idea.. and i ant diesel for the mpg. towing power. and i can make my own fuel