I don't think I have ever heard of a fuel-efficient Mercedes Diesel engine of any sort.... Maybe the newer DI engines could be if they didn't have so much damn emissions crap on them.. but they do. And then there's the problem with what if something goes wrong with it? You can't do nothin bout it unless you can talk to the computer... I did, however, run across a new-technology diesel today that didn't seem so bad.. check out a Kubota V3800DIT... Efficient, clean, about the same size as a Cummins 4BT and just about perfect, near as I can tell, for a Jeep!!!