Drive/Overdrive Fuel Consumption

[STEWARTL]

I have a 2001 Dodge 3500 Diesel Duellie with a Banks Power Pack. This is my first experience with a diesel engine. I am finding that either pulling my 5th wheel, or driving solo, that I get better fuel mileage in "Drive", then I do in "overdrive". This doesn't make sense to me. Can someone explain this to this first-time diesel owner? Thanks.

 

[Shovelhead]

The "Sweet Spot" for the 24V CTD is right around 1900-2100rpm.

That's where it likes to run and seems to be most efficient. HTH

 

[Boldt's Wagon]

Your profile says you have a 3. 54 automatic.



You didn't state if the 3rd and OD towing are at the same speeds, it is somewhat natural to drift up to a higher speed in OD. Towing a fifth wheel the major fuel consumption is due to air drag. A 10 mph increase will decrease milage 2 to 3 mpg and can overwhelm increases from shifting to OD.

 

[Gary - K7GLD]

It's an issue of mechanical advantage vs inertia and weight - the engine turns slower in OD, but must work HARDER due to the steeper gear ratio - sorta like walking with a load uphill instead of on the level... Same load, but ya gotta work harder to make progress...



Shucks if all we had to do to get better fuel mileage with higher gear ratios, we could all put 1. 1 differentals in our trucks - but it SHOULD be obvious why that won't work... . I hope...

 

[pwr2tow]

Strange, I find a 2 miles per gallon increase by towing in OD at 65 MPH. This was before my upgrades.



Ron

 

[Crazy Horse]

Originally posted by Gary - KJ6Q

It's an issue of mechanical advantage vs inertia and weight - the engine turns slower in OD, but must work HARDER due to the steeper gear ratio - sorta like walking with a load uphill instead of on the level... Same load, but ya gotta work harder to make progress...



Gary-Very well put.



Shovelhead-That's right where the "Sweet Spot" is for sure.

 

[Boldt's Wagon]

Originally posted by ronsram1999

Strange, I find a 2 miles per gallon increase by towing in OD at 65 MPH. This was before my upgrades.



Ron

That is about right for 65 in OD vs 65 in 3rd (2 mpg increase), and 55 in 3rd will be about the same milage as 65 in OD. The original post was questioning the same milage in 3rd and OD with no mention of the speeds in either gear.