I've worked on some westport engines the ISX in particular and it's very expensive to repair the injector's are two fuel diesel in the middle and natural gas on the out side and are very expensive 3k a piece and you have a lng tank on the side with a very expensive pump inside and if ya want dual tanks ya got to have two pump's and everything is proprietary to westport. You can't get nothing from anyone else. Had to get some seals for one and they where like 50 dollars a piece and tried to get from the manufacture and they said no it was proprietary. And they can be very hard to start if anything is wrong and it has two engine computer's that you have to have insight and westport software for. and the truck can cost a 100,000 more. I'm not a big fan