I have a 2004 CTD 4X4 quad cab 2500 SLT. I filled up tank. Drove 100 km exactly to my destination (all highway) at 100 km/hour and filled up again. I used 12.34 litres of fuel. I live in canada so that comes out to 23 mpg...not bad at all. No mods except tailgate down..

PS
I removed silencer ring after this trip. will it effect fuel mileage at all or not?

 

No difference, it will sound good though. Straight interstate my computer says 23-25 and its always about 1.5-2 mpg high.

 

The overhead computer(lie-o-meter) is always off by about that much. When you figure miles/gallons it's more accurate.

 

tailgate down doesn't help either.

 

why wouldnt tailgate down help? and the lie o meter is way off on mine. because the day i got 23 mpg the overhead said 26 mpg. and a week ago it said 31 mpg...so go figure.

 

Having the tailgate down doesn't help at all, it may even hurt. From what I've heard,with the tailgate down, air goes over the cab and drops down sharply against the bed andtailgate, which pushes down on the truck, adds more friction. With the tailgate up, air in the bed is constantly circling, so air coming over the cab cannot go straight down, it instead is held up higher than the bed and drops off behind the tailgate. If that makes any sence to you.

 

actaully the day lieometer said 31 mpg tailgate was up......

 

as you can see from my attached art work a small aerodynamic ball ciculates in your bed which is almost like an invisable cab allowing the air to flow over the truck being slightly more aerodynamic..... when the tailgate is down the air goes straight to the tailgate causing more downforce on the rear which is almost like carrying stuff in the bed.... and also ruining the aerodynamic design of a pickup...... sorry im not an artist the blue lines are airstream


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I know how bad the overhead comp is but I never fill up after a small interstate run so its my best "highway only" measurement. When I go get my new truck saturday I will know for sure and will have 300 miles worth of data.Good explanation on the tailgate thing tdmopar, Iwas justgoing to say because Isaw the test on mythbusters and they said so!

 

I only get 23 when Im going down a steep grade with the jake on. Best I have got on the highway was 19, But thats just me