I'm really hopping Jeep is able to get the new cherokee with the diesel motor up to 28-30mpg. If they can manage to get even close to these numbers in the real world the Diesel Cherokee is sure to be a huge hit!
Looks like a lot of threads will be "revivals" until more people are on the site. Anyway....
I agree that comparisons are probably better against the V8 because of the fact that for most people the choice of these engines involves performance and towing capability. Cost per mile is a good way to look at it too. One thing we looked at in comparing to the V8 is how long it would take to offset the initial price difference. If the difference is on the order of $4-5000, it'll take a decade or more to offset the cost from improved mileage alone, unless fuel costs change. We got our diesel for just a shade more than a similar Overland with V8, so I am certain on mileage alone we can make up the difference in fuel savings alone in just 2-3 years. It also helps that in our area we can find diesel for $0.40-0.50/g more than gasoline. The less the difference, the better.
I think the general consensus is that for a given load, the diesel is expected to do better than the V8 because of the fact that mileage drops off more rapidly for towing in a gas engine than a diesel. Seems to be the thought from other diesel oriented sites.
We're at 27-27.5 avg mpg so far. About a 50-50 mix. BTW, the diesel takes 8 qts or engine oil, not 7. Also have to replace fuel filters at oil changes, or every 10k miles. And then there is the exhaust fluid. You may see where it costs $8/gallon - I found it at Autozone, $15/2.5g, so not $8/gallon. That is an estimated every 10k miles thing too, 8 gallons total capacity. There are going to be some increased maintenance costs with modern diesels compared to gas engines, and certainly the potential for major costs if things-engine fail and aren't covered by a warranty. I think even today, costs of repairs on diesels tend to be higher than on gas engines, I could be wrong given some of the sophisticated technologies on newer gas engines.
I just picked up mine, I'm pretty sure the trailer tow IV is standard, (there are a lot of standard features with this diesel engine) and I think the diesel has a tow limit of 7400 lbs., vs. 7200 for the V8. I'll be looking to see what the actual MPG is in a few days, the dashboard calculator I think is factoring in the 0 mpg moments when the vehicle is idle into the average MPG. I'm really happy about the vehicle even if it had an MPG of 15 or so.