i only drive ~5 miles to work, and only get ~16mpg.

i only get up to 55 for about 2 miles, and then it's back to ~35 all over base, mostly idle in line to get around base.

the temp never gets up to 200, is that hurting my MPG?

I'm driving 7 miles each way this last week, and mileage is up some, temp getting close to 200 by time I get to work

 

Ya. The cummins really needs to be heated up for it to get the good mileage. Take it on a nice road trip this weekend and let her stretch her legs out a little. She'll thank you for it.

 

My winter mileage stinks because of my tires and the crappy winter fuel, 13 mpg. I got my new summer tires on now and am getting upwards of 18 with an automatic. The tires and temperature are the two biggest factors.

 

From around 70 degrees and up my mileage is increased. I have a 180 thermostat and if it gets to 200 I have to start backing off, its too hot.

 

The cooling system on the new cummins is made so the engine has less chance of overheating when you're hauling heavy in a hot climate...so it sucks when you're just putzin around in a cold climate. Even when you let the engine do its "auto high idle" around 1000 rpms it takes forever for it to heat up.

Although, you're in Jax, FL, so you don't need much of a warm-up. I'm thinking about moving there and I saw the overnight temp was in the 40's

You could let your truck warm-up for about 10-15 mins before you leave and that'll make things a little better.

 

I know in the winter my MPG is down 2-3 without some sort of winter front.