I left early Friday AM with Scott and Vanessa heading to Kentucky to pick up 2 pups from the last litter my Lab Spud sired. Scott was getting one and Vanessa was get one for her niece as a surprise. Anyhow, I filled up the evening before about 2 miles from my house, and tripped the mileage counter back to 0, as well as the overhead. Picking up Scott and Vanessa probably added 40 miles to how I normally drive down there, but I don't think it would've mattered one bit.

We left early (6:00AM), but it was hot by 8:30AM, so I clicked on the AC. It's hard to talk running down the highway with the window open!!! Got down to KY, hung out at Dougs with the pups, went and had dinner, went back to the pups afterward, and then drove to the hotel on Friday.

On Saturday (today), we drove to the restaurant for breakfast, over to Dougs, hung out there for a couple hours and then headed back to northern Illinois. I filled up just South of Mount Vernon, IL on the way back. 620 miles on the tank, and the DTE on the overhead was reading 36. Put in 30.7xx gallons and it figured to 20.2mpg.

But get this.....................that's running 2k rpm or about 68mph, with the AC on!!! Can you say "happy camper"????? It was 90* for most of the trip down and back, and I've always said that my truck gets super mileage the "hotter" it is outside!!!

Most rigs get better mileage the hotter it gets, even thou the peak power is down from less dense air the motor is able to cruise easier. It goes back to my theory on winter mileage. I don't think the fuel plays a measurable part, it's the cold tires, cold fluids, and cold dense air providing more resistance, so when it's hot you get the opposite. I also don't think the a/c even effects these motors! I just wish it was flat enough around here to get good mileage, always climbing it seems like.

Also got to remember with the A/C on you dumping all your cab heat over the top of the intercooler warming the intake air even more. I typically see better MPG with the A/C on than with it off because heat factor. It small jump but its there. My last few high marks have been down with temps at 70-80*F...

Good deal

Forgot to include this info in my original post.............whilst cruising on the interstate at 68mph+/- with the AC on.................EGT's were a solid 600*, boost ran an even 5psi over level ground, and LP pressure was 24psi on level ground.Sorry, but I wasn't checking my RP gauge while cruising with talkative passengers!!!!:doh:

Holy crap you run a LOT of psi to your CP3. Bosch peaks their range at 15, and I hear 12 is the ideal pressure.68 ± should be about 18,000 psi ± 500. I see about 17.8 flat and steady, but will jump to just over 19 on a small hill.

Holy crap you run a LOT of psi to your CP3. Bosch peaks their range at 15, and I hear 12 is the ideal pressure. 68 ± should be about 18,000 psi ± 500. I see about 17.8 flat and steady, but will jump to just over 19 on a small hill.

Either my rail pressure gauge is bad or my CP3 is going bad but I never see 19k going 68. Always around 12-15. Unless I get on it. --- I am here: http://tapatalk.com/map.php?qlzifd 2003 Ram with gauges and a Smarty! Not much more. Sent from my iPhone using Tapatalk

Either my rail pressure gauge is bad or my CP3 is going bad but I never see 19k going 68. Always around 12-15. Unless I get on it.

You have an 03, very different rail pressures.

So are my pressures where they should be? --- I am here: http://tapatalk.com/map.php?dzgrzs 2003 Ram with gauges and a Smarty! Not much more. Sent from my iPhone using Tapatalk

Those pressures look correct for 2K rpms.

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Here is what I look like at 68. 75° out, a/c was on. Rolling flat at 2800'. My EGT's drop about 50° cruise as I near sea level, and go up as altitude increases. Rail pressure was about 17.8K when I took the photo.

I haven't ever verified it, but in conditions like this the exhaust manifold blankets are reported to raise EGT's from low flow and insulation.

There are some things I can take as gospel when it comes to mythbusters. One them, being whether or not your mpg is affected by the a/c and windows when driving.Their results cam back as:If going 55mph or under, it is more fuel efficient to run with your windows down to keep cool.If going over 55mph, it is more fuel efficient to run with your windows up and A/C on to keep cool.- Its a matter of aerodynamic drag on the vehicle that overcomes the increased load on the engine to displace the difference in energy loss.

There are some things I can take as gospel when it comes to mythbusters. One them, being whether or not your mpg is affected by the a/c and windows when driving. Their results cam back as: If going 55mph or under, it is more fuel efficient to run with your windows down to keep cool. If going over 55mph, it is more fuel efficient to run with your windows up and A/C on to keep cool. - Its a matter of aerodynamic drag on the vehicle that overcomes the increased load on the engine to displace the difference in energy loss.

I saw the episode you are speaking of and they performed on automobiles and not a truck like ours. I do know that the compessor has to put some drag on the engine, but I would think it would be less noticable to the Cummins. I have never really notice any mileage chnge when I run mine, but have never tried a controlled test to see if that is the case though. So may maybe we can make them do a do over in one of our trucks.

good job on the m.p.g.'s...another thing i would help thank that to..is all of the winter blended diesel is all used up...the refinery i work at..i have asked some of the lab people over there..and since we .here in s.e. kansas did not have that harsh of a winter like last year...we didnt make that big of a batch of the winter diesel...i notice on my first fill up bout a month ago my m.p.g.'s went up...again ...congrates!!