This is the #1 question posted in 2nd Gen. It's really simple: The 5.9L is a big, fat, thirsty engine. When my dad was running a delivery service in a small town in BFE called Ely, NV he bought a brand new 73 Dodge Tradesman with a 360 and 727. That thing got 10 mpg on a very good day and it wasn't uncommon to get as low as 5 mpg. The point is they have ALWAYS been pigs. Check the plenum and drive like there's a raw egg under the pedal. I get ridiculous mileage(relatively) with my 5.2L(19 mpg average now-best couple tanks a tick over 20 mpg) by accelerating slowly(like 20-30 seconds to 50 mph), 45-50 mph tops and NEVER exceeding 55 mph. I don''t know if it makes any difference, but I installed platinum plugs and wires about 10k miles ago. But I'd be willing to bet that you'd never recoup the cost of anything like a CAI in mileage-it's all about how you drive. I'm semi-retired so I can drive as slow as I need to. I don't think it's practical for very many people.

 

I have been told a 180 stat will hurt mileage unless you have an sct tune loaded..since it runs rich until 195 degrees is reached and you will never get there with a 180... I ran both and wemt back to a 195..... with that and generation 3 injectors I'm getting the best mileage I ever have. (14-15 highway) with 35" mud tires and 5.5" of lift and 4.56 gears loaded with canoe on the roof and camping gear and passengers....

 

cai did nothing for my mileage. after the plenum and other upgrades i actually lost 2-3 mpg. granted i did get bigger tires (285 up from 265) so maybe thats where my 2-3 went?

 

That and the lift would be the culprits.

 

yup that will do it... Along with about a 15hp power loss to the wheels from the bigger tires... you may see better results if you leave the od off...
what did you do to the plenum? just the plate replacement? or kegger mod? CAI isnt for mileage it allows more , cooler air for more dense molecules... thats gonna require more fuel... everyone wants more power with less fuel.... its an oxymoron in most cases and aint gonna happen with bolt ons in most cases...

 

I should put a thermometer on my CAI pipe. It gets really warm its made from aluminum and painted balck. I think the stock air cleaner got cooler air.......Any way my mpg went up but again it was time for a new air filter and a mouse had made a home in the old air hat causing great restriction.

 

yeah the plate, plug, wires, water pump, timing chain, new o2's F&R, all the goodies like that.

and i can see the 15hp loss with bigger tires. still feels a bit sluggish. but i also know the gearing is holding it back as well.

 

Are you talking about 3 gen ram, stock injectors

 

I have a 3/4 ton with the 5.9 and i get 9 to 10 with nothing in it around town, Open up the exhaust with some long tube headers and about ehhhh 2.5" to 2.75" cat back and a nice free flowing intake you should get 12 to 13 maybe..... If you can keep your foot outta it

 

And there my friend, is the rub. Doing those also gives ya more power... which people seem to like to play with. So, they get WORSE gas mileage.