My Ram's diesel tank doesn't have a cap. However, it is located next to the DEF outlet. Earlier in the summer when I was in a hurry to add DEF, I stuck the spout in the diesel tank and almost started putting DEF in the diesel tank. It could have been pretty disastrous, but luckily I caught my mistake in time. I figured I would have to install a diesel cap to make sure I don't do it again. So far it has worked great for this purpose. I would give it five stars but it's a bit hard to walk away from (a small price to pay for your work).
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