'05/'06 E320 CDI MPG @ Start up?
 

My '06 E320 CDI's mpg @ start up, according to the onboard computer, had been just a tad over 30 mpg for as long as I can remember. Recently, it's running 25 +/- @ start up. Wondering what the trouble may be, as well as what other like CDIs are running here?

If you're not moving the number of miles driven is zero. Divide zero by any other number and you get zero!

(Sorry about that - needed a bit of fun)

I imagine the read out on your gauge is based on several parameters such as outside air temperature. If the car "thinks" it is cold perhaps it becomes less hopeful about your MPG possibilities?

I'm hoping its not "Man is it ever expensive to drive an economical car" scenario!

Outside air temp plays a role as I've observed on other vechiles equipped with mileage consumption displays.

Skid Row

I usually start up at around 27. I do insert a flexible foil covered Styrofoam sheet just before the radiator. It has been my experience that diesels have a hard time staying warm during winter and it plays havoc with the milage.

On a summer day, my 11 miles commute to work will reflect about 34mpg. It takes about 3 miles to get to temp.

On a winter day, that 11 mile trip will only be about 26mpg, taking much longer... perhaps 8 miles to get up to temp.

Having said that, when my thermostat broke and was stuck open, the mileage plummeted, getting as low as 17 on a tankful. I was amazed at how much difference a stuck tstat made.

I have observed the same on my 05, and my wife's 06. I have attributed it to Winterized diesel. a lower BTU content because of the #1 oil blended with the #2. I have no idea if it is sold in your part of the country, but it would make sense to send the same blend everywhere, plus, with an 800 mile range on some diesels (like ours), you can get to somewhere cold where you would need that in your tank.

Today @ 50F......
 

Indicated 31.4 mpg @ start-up cold in my garage. mpg dropped precipitously as I started my 3 mile drive to 24 or so mpg. Must be the colder temps. at start up that drop it (mpg) so rapidly. The water temp. edges Up very slowly to normal operating temp. in the Wintertime.