Um, there actually is a 4.0 litre V6 - but it's a Ford engine. The V6-244 used in the Explorer, Ranger, Aerostar, and (I think) some F-150 and E-150. :P
Also, I find it interesting that, after DCX said that the "inline six engine is dated and unsafe" (the former, perhaps. The latter, really? BMW gets consistently high safety ratings, and they've been using inline six gasoline engines for the last 60 years or so...) that General Motors should be resurrecting their inline six in VORTEC trim - with a displacement of (get this!) 242 cubic inches! (242ci ~= 4.0L. Calculated displacement of our 6-242 engine is right about 241.5ci...)
Hell, I think BMW has been using I6 engines slightly longer than Jeep has - and Willys started with the F6 engine in the late 1940s or early 1950s! Displacements of the early Jeep sixes? 226ci in L-head or F-head, 161ci in F-head (and probably L-head,) and let's not forget the 230ci "Tornado" OHC inline I6 right around 1960, with the really funky cam profile (as I understand it, BOTH valves are driven off of a SINGLE cam lobe...)
Volvo uses an I-6 in their XC90 SUV as well, at least they were very recently anyway 2007+. And Volvo's big marketing claim to fame is "safety".
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