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TDI swaped Rubicon


New Member
Aug 1, 2021
North Texas
So to start things out I'm tired of 13 mpg with the 4.0 especially with gas being almost $5 a gallon. I ran some numbers on and a diesel is just more economical. In my calculations I set diesel to be 20% more than gasoline. As for the estimated mpg, 15 for gasoline and 22 for diesel as to be on the more conservative side of things. Diesel comes out on top for cost savings which is a major motivating factor along with the possibility for increased driving range. The project is just starting as I picked up the engine and it's harness earlier this week. I hope to keep this project well documented so others may find it useful in the future.





TJ Enthusiast
Jun 1, 2020
Springfield OH
I dont want to sway you back to gas since this will be an awesome build and it will for sure accomplish your goal, but I went the basic white girl LS swap and I have gotten 16mpg in the most un-aerodynamic configuration (no door or top) compared to 11mpg with the 4.0. Even gotten allegid logs where it shows an average of 19mpg for a trip going to work in the city. I have yet to check any fuel mileage with a top and doors or any extensive highway driving yet, but plan to do that.

I think going with a torquier engine like the TDI motor will still help all around, but you will see the most gains below 50mph. At 55mph (at least with no top or doors) it diminishes gains real quick so I am starting to work on aero mods to a certain extent like modifying a front air dam from a JK to fit under the front bumper and putting a seal between the hood and grill to help air flow a bit better around the hood. Also the grill inserts that are more solid in the middle making more of an air dam seem to help too as opposed to no inserts or open webbed inserts.

I am in the same boat as you except I did my LS when gas was $1.50/gal and did not care as much. I still don’t care as much about saving money at the pump but extending range to go more places. Though cost savings is slowly becoming a bigger motivator to doing these fuel saving mods.