Funny how things sometimes seems almost spooky connected. Just had a friend tell me his Magnum, which has been running 26 PSI in his 44 PSI rated tires and had his tire pressure raised to 38 PSI front and 40 rear last week, has had a 4 MPG increase fuel ecomony. Needless to say he is tickled pink. He was always mad that I got better fuel mileage then him (identical cars) and I had always told him to air up his tires which he thought was bs on my part.

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91 MB 300D 2.5L Turbo. Her's

05 MB E320 CDI. Mine

Tire rolling resistance, as determined by tire choice & inflation pressure, is the largest influence on mileage following vehicle design & driving style. The placarded tire pressure recommendations are designed by the OEM to provide that plush, solid feel that most buyers want, but at the expense of mileage & handling. Fill them to suit your preference, within the limits posted on the tires themselves. Also, turbodiesels must be broken-in before optimum mileage is attained, which can take quite a while (some say upwards of 60,000 miles). You can hasten this by moderately loading the engine (towing, hard acceleration) whenever you can during the break-in period. Engine treatment can also permanently determine your engine's characteristics. Extended high-rpm operation can cause cylinder glazing while excessive idling can result in glaze-like cylinder deposits, both of which are permanent detriments to efficiency, power, & emissions. Extended high-rpm operation probably isn't an issue for us in the U.S., given the 545RFE, but excessive idling may be for some. A diesel should never be idled more than it needs to be. It does no good.

This is a good article on breaking-in a diesel:

http://www.thedieselstop.com/contents/getitems.php3?Breaking%20in%20a%20Diesel%20Engine

There's also a lot of discussion on http://tdiclub.com/

Here's a nicely comprehensive list of fuel economy tips:

http://www.ultimatesyntheticoil.com/Improve_Fuel_Economy/Increase_Fuel_Economy.htm

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03/15/2006 Jeep Liberty Limited CRD w/86,000 mi. Engine lube pump, Provent, V6 airbox mod, Magnaflow, gauges, Amsoil all around, & Wix air filter. Sunroof drain blocked on receipt, stubborn fuel leak at 2200 mi, 3 jammed windows, & 1 bad alternator decoupler, but it's still a keeper!

My '05 CRD has never gotten LESS than 20 mpg per tank since the first tank of fuel--hand calculated. My best tank was just over 31 mpg--that on a higway trip off of the Interstates at 65 mph or less. Most of my driving is on the open highway, with some off-roading mixed in--all of it over 5,000 feet elevation and most in the mountains. I don't do jackrabbit starts, etc., but I don't baby the CRD, either. I see about a 15% decrease in fuel economy when running winter blend fuel. The CRD is not my daily driver, so I don't use it for commuting unless the weather is awful, which, for the past couple of winters, has been infrequently.

As a point of comparison, I got up to 25 mpg out of my old '98 Cherokee on a highway trip at 65 mph or under. Drive 75 and that dropped to about 20-21 mpg. Throw in some off-roading, and the mileage dropped as low as 14-15 mpg. Based on that, I would guess that the CRD gets about 20% better fuel economy than the Cherokee on the highway, and probably 50%+ better economy than the Cherokee when off-roading. Because a diesel can run on a much leaner fuel-to-air mixture than a gasoline engine, especially at idle and lower rpms, that conclusion probably makes sense.

It's unreasonable to expect that any 4,000 lb. plus vehicle is going to get very good fuel economy in stop-and-go city driving. As far as I'm concerned, that's not what the CRD (or any other heavy SUV) is really designed for. That's why I don't commute in mine. I have a cheap, used, relatively economical "beater" for that.

Mine dropped when:

Added Gibson exhaust -Turbo spools faster and has really cool sound
Added 30" tires - uncalibrated speedo
Added 1.5" daystar - pushing more air

And it is going to drop some more when I go to 31"s