I have a Jeep Liberty CRD and have made some changes recently. Even tho I added a lift and bigger tires, I have increased MPG of diesel by 14% (city) with some small changes. I aired up to 44psi, no idling whenever possible, slow starts and slow stops, High G turns to carry speed, Aluminum Skids to save weight and flatten the bottom side of the Jeep, 5 AirTabs on the rear roofline to clean air off the back (I should do more down each side but the look is horrendous), coast whenever possible, ect. They have all worked and once you get used to the new driving style, it becomes second nature (coming from a former Mazda 12 and 24 hour enduro racer). I am a big Amsoil Fan but have stayed with a 15-40W (AME) for engine protection. Also installed a 2002 Air Box into my 2006 with an Amsoil EaA 100,000 Air Filter to get colder/cleaner air. Don't really worry about covering radiator openings in San Antonio, Texas...the winter temps are hardly ever bad. I am probably going to remove the backseat since I never use it and build a lightweight flat floor in the cargo area.
2006 Jeep Liberty CRD
...Founder of L.O.S.T.
OME 2.25" Lift w/ Toyo Open Country HTs 235/75/16s
ASFIR Alum Eng/Tranny/Transfercase/Fuel Skids
2002 Air Box Mod...Air Tabs (5) on Roof...(3)each behind rear windows
Partial Grill Block with Custom Air Scoop and 3" Open Catback Exhaust
Lambretta UNO150cc 4 Stroke Scooter