Hi there, I have a 2012 Ford Expedition XL base that I want to do engine swap to 4.2L V6 engine instead. It's the lightest curb-weight 2007+ Expedition I can find, and it only has 5-passenger seats, no 3rd row, save 100 pounds, it's not EL, save 300 pounds, and also no high-tech goods, save 50 pounds. XL was discontinued after 2012 year, and got more heavier.

Don't ask why I want a lower-power engine, a V6 pushrod Expedition has been my dream ride for a while now. I have a 2008 F-150 V6 that I like to do engine-swap exchange, and my 2012 Expedition will get 4.2L V6, while 2008 F-150 will get 5.4L V8. I found 4.2L V6 MPG up to 4 MPG higher than V8 on highway if driving all flat-terrain, but both have same MPG if going uphill. Is this doable?

However, I don't know if I can keep the 6-speed auto transmission in 2012 Expedition and paired it with 4.2L V6 together. 2008 F-150 only had 4-speed auto. Is transmission-swap required also?

I also have the option to go with older 2006 Expedition with 4-speed auto at its last year if transmission-swap won't work, but 2006 is starting to be old here. But 2006 Expedition is 200 lbs. lighter than 2012.

No one has done this before, and I will be the very-first pre-2014 Expedition V6 owner in United States. Thanks for your help.