Hi All, I'm new to the forum here, although I have made a few posts already. I recently bought my 3rd new Dodge Ram and I have some questions. The new truck is a 2007 QCSB Hemi 1500 4x4 with 20" wheels and 3.92 gears. I'm currently at about 1500 miles and averaging about 9.5 mpg around town and 13 mpg on the highway. Will my mpg get better as the truck breaks in, or am I going to have to get used to it? Does the wheel size and gearing have that much of an impact on mpg? In the other Dodge trucks I owned, a 2000 QCSB 5.9 1500 4x4 and a 2002 QCSB 4.7 1500 4x4, my mileage always remained constant over the time that I owned them. Since this is my first Hemi, I'm wondering if the same will hold true with this engine, or can I expect the mpg to get better. I've searched the forum for answers to my questions but I haven't found any conclusive answers. Any opinions are greatly appreciated. Thanks.

 

The vehicles fuel economy will be reduced during the first while of driving. Your fuel economy will improve as time goes on and the engine breaks in. It all depends on how/where you drive too. Also, depending on your location, you may be buring "winter blend" fuel. It is an E10 blend so you will notice a reduction in your fuel economy from that too.

 

I had a '98 1500 RCSB 4x4 with the 5.9, a 3" body lift and 35" tires. Never got into double digit MPG's in town and was lucky to see upper 11's on trips. My '04 1500 QCSB 4x4 got about 14 in town and maybe a hair above 17 on trips (as it's on '04 I don't have MDS). This was right about what the window sticker claimed and the mpg gains were a lot better with the Hemi than the 5.9 as advertised. Most people also claim at least as good fuel economy with the Hemi as the 4.7 people are getting.
I'm shocked you are getting such poor fuel economy, especially with MDS going for you. Maybe a combination of break-in plus the crappy winter blend gas.
I'm seeing about 13.5 in town and about 15.5 highway now with my Hemi with 4" suspension lift and 35" tires, plus a whole lot more HEAVY mods. I'm weighing in at just a hair under 7000 lbs! I've also done 4.56 gears and a lot of mods that produce not only more HP but better fuel economy as well, which is why I think I've not lost all that much MPG's even with all that added weight...

 

It does take a while for the Hemi to get limbered up. Someone said they were told it takes 12,000 miles for the engine to "mature".

 

The short answer is yes, you can expect the mpg to get better. MikeHTally is right, the mpg will improve as the Hemi "matures" or "breaks in" , which is different for each motor, but it should be reasonably broken in by 10,000 miles. Some owners report continued improvement up to 50,000 miles. Of course, if you are like me, you may never see an increase in mpg, because the more I drive my Hemi the more inclined I am to put my foot in it...thus poor mpg, about what you are getting now. I think it is gas money well spent!

 

I was told by a dodge service rep that the four 02 sensors on the ex system nead twenty thousnad km ( 15,00 miles ) to break in, then MPG improves.

 

In a nutshell:
tires can have up to a 3 MPG effect
with mudder tread wide tires being worst for hard to roll
and lower tire pressure making any tread design worse.

The 'break in' improvement in MPG is usually 1 by 30,000 miles
and another +1 around 100,000 miles
due to reduction in piston ring tension,
carbon deposits in the cylinder raising compression ratio
and hydraulic lifters leaking down more (Rhoads like) as they wear.
The break-in is not because surfaces get worn smooth.

Drivetrain and gears have effects on MPG.
Key ideas are keeping the throttle blades open (Hemi 5.7 MDS works this way)
and reducing piston speed to the 800 to 1200 foot per minute level
(it is not rpm...it is piston speed that determines where fuel economy is best)

More info in this long read down a ways in the 'Drivetrain Mods' section:

https://dodgeforum.com/m_447500/tm.htm

 

My truck still gets 9.5-10 mpg in town and has also never topped 12-13 on extended interstate cruising at ~ 75-80. Same wheels, same gears.