The civilian version of these motors will also run on other fuels, as long as you stay with the mechanical injection pump. The mechanical IP was used up until 1993 on the 6.2 and 6.5.
1994 was the start of the electronically controlled IP. The optical sensor used with this IP won't work properly with anything other than diesel fuel. The good thing is that any newer 6.5 motor can be retrofitted with the mechanical IP.
The mid to late 90s era motors built by GM have a reputation of poor quality with the block casting and machining while the early 90s 6.2 and 6.5 have a much better reputation.
However, in about 2000 Navistar took over from GM in casting and building these motors. Navistar changed the metallurgy and revamped the castings to get a a much better and stronger block.
It is possible now to get military takeout motors with Navistar cast blocks. I've read of a number of people who got these mil takeouts who pulled the heads to check them and change from the TTY head bolts to ARP studs. All that I have read about, except for one, have reported that the valvetrains, heads, and cylinders looked like fresh rebuilds.
To make a long story short, there are mil takeout 6.5s also now available. Almost everything will interchange between the 6.2 and 6.5, older or newer, military or civilian. It is possible to put the 12V mechanical IP on any of these motors and use other fuels.
Don
