Teflon tape is not effected by diesel fuel, but if a piece of it gets loose, it will not pass through the diesel pump or injector. Personally, I wouldn't use it, but would rather use a good quality pipe dope and only use enough to get into the threads. When in doubt, use less ........ you can always add more. As I have said in the past, Teflon tape is for old worn threads and pipe dope is for new threads. Use the correct sealant and you will have a better chance of success. Also, pipe threads are tapered...... the more you turn them in, the tighter that they get....... at a certain point, you will crack the casting that you are screwing into. I have seen plumbers do this with Teflon tape on a new installation when Teflon tape first came out. I rarely use it any more..... pipe dope is better and it is approved for most gas, gaseous, and liquid applications....
