I know this topic has been beat to death on here. Heck I have a thread or two about it myself. I am just puzzled that 10.16 MPG was my last hand calculated tank considering what I have. Heres the run down.

2008 Hemi Quad Cab Big Horn
3.92 gears
20" wheels stock tires
2" level kit
Vararam Intake
Flex a Lite 183 E Fan
Jet 180 Thermostat
Superchips Tuner running Performace 91 tune and a custom shift schedule
Magnaflow Y pipe
Custom side exit cat back (cherrybomb muffler)

I am running all royal purple fluids. Truck has 45K on it and plugs were done at 38K, replaced EGR and cleaned throttle body at that time. I run 2 ounces of Star Tron in every tank and run 93 octane.

My last three fill ups were all roughly 9.8-10.3 MPG. What the heck gives? This is worse than stock. Now granted I live in hilly western PA. Also, 90% of the driving done with this truck is with 5 mile and shorter trips. Could the truck never be getting out of a "choke" mode and just dumping fuel all the time? The truck runs strong, way better than stock. I just cannot believe that with the mods im running the MPG is that bad. I apologize for the rant. I know trucks are trucks and will never get good mileage. I also know the hemi is prob the worst of the big 3 trucks. I just see so many guys on here getting considerably better mileage (3 MPG or so) with very similar setups.

 

Your truck is a couple years newer than my 3500, but I was struggling with low fuel mileage in my CTD last month... then I noticed that my calipers on the front were dragging real bad. Got that sorted out, new brakes all around (not directly related to this but needed to be done anyways) and my mileage has returned to were it should be.

Just a thought.

 

Brand new brakes and rotors front and rear were installed at about 40K

 

that is very weird I get better then that with my 35's and you have a lot more done to yours.

 

Depends what your short trips are. I'm always around 10mpg with my short trips which are a few miles in the city. Mostly stop and go with nothing over 35mph. And that includes me using a window scraper instead of letting it idle for hours every week inthe winter and the AC's always on in the summer. I can baby it all day long but it never changes much with seasons or gearing for that matter. Sad part is that I get about the same mileage hauling 8500# as I do in the City. Go figure.

 

ITs called Winter, and oil compaines change up thier flue formulas to adpat to colder conditions..
Check out othier truck fourms, they two are reporting bad mpg...

 

I get similar MPG with similar mods and same gears. It's just the short trips. All of my city driving is to class on campus which is actually across the street from me but to drive to class is about 3 miles. Short trips are never good for MPG is any vehicle.

 

I gotta travel at least 15 miles to get 13-16 MPG, otherwise I'm looking at 7-10 MPG. If I just drive to the end of the neighborhood to the gas station on the corner and back home being as light on the pedal as possible, I get 5-6 mpg. Oh, and all your mods LOWER your MPG's (except the electric fan) especially that performance tune and low thermostat makes your truck take a lot longer to hit closed loop operation and makes it dump fuel for longer.

 

I guess the question is:

Should I be buying 89 in the winter, or just go 87? I'm not really knowledgeable about fuel, but I do run at least 89 all the time, no exceptions. I also let it run for about 5-8 minutes before I start driving, to let it warm up a hair.

 

It depends. You really only want to go up on octane rating if you experience spark knock or sometimes missfire on the lower grade. The higher the grade, the more resistant it is to detonating by compression and it will burn slower and hotter. Heat is the enemy in engines. Spark knock comes when the compressed gas ignites before the spark plug has a chance to properly ignite it resulting in a poor, inefficient, double detonation.