we use diesel here on post.. now I have seen the Fuel caps on the M998's and M11... (hummers) state "diesel, Jp8" i would think that it wont hurt a 6.5 it wont hurt a 6.2... just add a quart of motor oil or trans fluid to lube her up.
Don't add motor oil or transmission fluid. Both are not designed to burn and can leave deposits on the combustion chamber and injectors, and the friction modifiers in ATF can actually be worse for the IP in some cases. All sorts of trace metals and materials are added to both that do not burn and get left behind.
If a proper lubricity enhancer is not available, the best way to go is two cycle engine oil. It is designed to burn without leaving harmful ash and is intended to dilute in fuel to increase the lubricity.
A diesel can use JP8 no problem generally. You lose about 10% of your power. The issue comes with lubricity when the engine has components that are designed to be fuel lubricated like the 6.2/6.5 IP. That said, stick to one or the other if you can. If you run diesel for a long time, you will build up algea and sludge in the fuel tank. JP8 acts like a detergent and when you switch over it will kill that algea and all that crud will move to your fuel filters. That is an ongoing problem for those of us in the USAR and National Guard where we can only buy diesel locally, so we run it all year, but when we go to annual training suddenly we are running JP8 at the fuel point.
The other issue with JP8 is one of viscosity in hot weather- it can break down to the point where if the engine is shut down it will not restart until cooled. It is worse in cases where the engine idles a lot. It took TACOM a long time to even admit there is a problem, as they seem to be unable to duplicate it in the lab, but they are coming around. Having been there in the field I can say 100% it is a real problem. If you have AKO access do a search for "hot no restart" for lots of info on the issue of IP's, JP8 and heat.
