Not Q45 specifically related but maybe you all can help?

[rsiwicki]

I have had my '06 CC LE without Big Tow & 4x2 now for 2 months and 3,500 miles. Since the 1,500 mile break-in period, I have been aggressively driving the truck with many WOT runs in city driving getting at least 13.5mpg with a high of 14.1 mpg one week (foot must have been tired that week) and so I made my first road trip from Miami, FL to Destin, FL 650 miles each way. On the way up there with tail gate closed, cruise control on, without a bed cover I got 16.6 mpg on the highway. On the way back down I dropped the tail gate and got 16.9mpg. This is all probably averaging around 75~80mph with only 1 stop mid-way on the 650 trip.

My question is that if my city mpg is around specs at 14mpg then why is highway not even 17mpg when it should be around 19mpg according to specs.

Also I have only used premium 93 octane since I got the truck as I figured ti would be better to break in the engine with better gas and will be switching to 87 octane when I fill up again in the next few days for the first time as it was designed to run on 87 octane.

I guess I can officially say the tail gate up or down myth is now verified that mpg is only 0.3mpg better when down.

I am not really complaining about the overall gas mileage as it is still better than what I was getting in my Q with same driving habbits, but the difference or lack there of between city vs. highway puzzles me.

[ScottJackson]

In my past experience with trucks, they eat quite a bit more gas cruising at 75+mph compared to 60-65. Probably quite a bit more wind resistance as speed increases compared to something with a low C/D like the Q.

[jamesmost]

as well Rob no matter how hard u try todrive like an average driver, I know for sure that ur foot is Heavier

[Q45tech]

The EPA test for highway is at an average of 58 MPH and a never to exceed 60.5 mph not even in a pass - AC must be off. Your gasoline must meet as built BTU program standard.............current gasoline [non oxygenated] is down by 6-9% from factory test.

I consider you lucky to get 16.5 instead of 19 considering the way you drove [speed].

[qsiguy]

Bigger vehicles aren't effected nearly as much by small changes as smaller, lower powered vehicles. I drive a '93 Toyota 2wd pickup as my daily driver. I drive 75 miles round trip to work and back every day plus any running around I do. I try every trick in the book to increase mileage. The truck had a rack on it and I averaged about 23.5 mpg mixed city/freeway. Removing rack gave me an average of 5 mpg better same driving. Putting tailgate down has given me an average of 1 mpg increase. So now I am averaging 29.5 city/freeway mixed. I have only done one all freeway trip in the last few months and got 31.8 mpg doing 80 mph with tailgate up.

My brother has a 4x4 Dodge cummins diesel and his mileage barely changes from city to highway, heavy foot or light foot, up hill or down.

The Q gets about 17-18 mpg on that same commute.

Don't know what this has to do with your question but thought I'd share! hehe

[Q45tech]

You must compare engine displacement to engine displacement, then correct for rpm [gearing]. The whole world taxes DISPLACEMENT to force efficiency except North America.

[redmanfx]

You sold your Q. This is how it gets back at you for saying "goodbye", it brings your new vehicle's MPG down to it's neighborhood.

PS- It also helps to take it out of 4WD! Being that you're in Miami and have to have a 4x4, I just wanted to clear that up with you.

Your NC Beach bum signing off,red

[rsiwicki]

thanks guys for the help...I was just surprised about the how speeds above 60mph really affect mpg figures. I still can't believe I am only getting 3 mpg better on the highway vs. hard city driving. No big deal as it is still better than my old Q. Others in a different Titan forum have posted similar results.

[guadofreak]

anything above 60-65 REALLY affects truck MPG. Also mythbusters did a show on the tailgate up.down theory.

It was proven that tailgate up without a cover made the best MPG. They had two identical trucks driving the identical stretch of road. The truck with the tailgate down was about 1mpg less than the truck in the normal position. They did a test to show the vortex created in the bed of the pickup truck with the tailgate up causes the air to flow smoothly over the rear of the bed. Where having it down causes the vortex to be non existant and actually causing downforce and increased drag.

[Jeff Williams]

My old NISSAN XT V6 got worse gas mileage when I put bigger, wider tires on it. The cold air induction and flowmasters helped a few MPG as well.

That monster should net you better gas mileage, by just dropping 5 MPH on your trips. The improved gas mileage should lengthen the amount of time you can be at speed, and actually get you to your destination faster, with less fuel stops. (Kinda like not having to shift into 3rd at the dragstrip).

I bet your fuel mileage will improve with lower octane gas, too. I got better gas mileage on mid grade fuel than on premium in my NISSAN truck.

[Rex]

... That monster should net you better gas mileage, by just dropping 5 MPH on your trips. The improved gas mileage should lengthen the amount of time you can be at speed, and actually get you to your destination faster, with less fuel stops. (Kinda like not having to shift into 3rd at the dragstrip) ...

Jeff, I thought you were a NASCAR guy at heart .... that's F1 talk there .

[louiegz]

I guess I can officially say the tail gate up or down myth is now verified that mpg is only 0.3mpg better when down.

That show, Mythbuster did a thing on the tailgate thing. I think they busted the myth.

[DrewQ45]

I guess I can officially say the tail gate up or down myth is now verified that mpg is only 0.3mpg better when down.

That can also depend on your truck's aerodynamics and the drag coefficient where the tailgate is concerned. My Dodge truck has a slotted tailgate and the OEM tailgate sits in the garage still new!

Even if it's saving .2 mpg, it's still worth having it when it's calculated over the lifetime of the truck. Right now it's sitting at 130K.

130000 x .2 = 26000 Miles saved!

A great way to increase gas mileage is to increase tire pressure on long highway trips.

Drew

[jamesmost]

oh yeah Rob shooo shoooo get outta here

[elwesso]

oh yeah Rob shooo shoooo get outta here

Thats right... hes not dealing with being sans Q very well!

[qsiguy]

I saw that Mythbusters episode as well when they tested the tailgate up/down theory. I tested it myself with positive results. I am averaging 1 mpg better with the tailgate down so I think the myth can go either way depending on the make/model.

[defrag010]

It's funny that this topic was brought up, because I had been getting about 12mpg in my '96 ram 5.9 auto around town for the past few months.I took it on a 700 mile round trip this weekend, and I averaged 20.5mpg while cruising at 80mph plus about 40 miles of city driving. I have smaller tires, so 80mph on the speedo = about 74mph in real life. The engine was turning 2200 rpm.It's lowered alot, has a bed cover, and has the usual intake/exhaust mods PLUS a mopar performance r/t cam. I think the lowering and bedcover helped me out a little bit.I filled up at about 2.77 a gallon from below empty, and I was surprised as hell when I made my first gas stop when the gas needle went below E again that my trip odometer said 515 miles!