Drive 65mph, NOT 70mph!!!

[thirstyturtle]

I know there's a lot of talk about MPG on here and I wanted to share a little story from this morning.

My wife and I decided to drive to the beach this morning to watch the sunrise and I took it upon myself to perform a little experiment. The drive to the beach for me consists of about 120 miles of Interstate with a posted speed limit of 70 MPH, and then maybe 5 miles of secondary roads from my house to the interstate and from the interstate to the beach, so for arguments sake, we're going to call this 100% interstate driving. I filled up my tank before we left (at 3AM) and on the way there I went exactly 70 MPH with cruise on the whole way, it's pretty much perfectly flat as I'm close to the coast. I filled up when I got there and calculated my gas mileage. I set the cruise on 65 MPH the whole ride home and filled up again, calculated the mileage.

Here are my results, keep in mind I'm in a 2006 Sport V8 4x4 with Daystar 2.5/1.5 and 265/70/17 Firestone Destination A/T's (44 lbs a piece). the distance read by the odometer was multiplied by 1.035 to account for the larger diameter tires. Also, because of the tires, the speeds were more like 67 and 72, but the speedometer was reading 65 and 70. Here you go:

~120 miles @ 70 MPH: 14.2 MPG
~120 miles @ 65 MPH: 17.1 MPG

Both of those values were exactly 1 MPG less than the computer reading. Also, for poops and giggles, while driving to my friends house this morning on the interstate I reset my computer while going 55 MPH for about 10 miles on similarly flat roadway and the computer read 18.7 MPG which would translate to about 17.7 MPG realistically.

I've decided I'm never driving 70 MPH again, it took 8 minutes longer getting back over the course of 2 hours and saved me about 1.5 gallons, which roughly translates into a Big Mac, large fries, and giant sweet tea.

In closing, I'm pretty pumped to be able to get 17 MPG with a all-the-time 4x4 V8 that's lifted with All Terrain tires, go T4R!!

 

[rockwall]

Very impressive research. My computer shows between 20-21 on the highway at 60-70 mph speeds. My truck is not lifted (it will be soon) and has stock size replacement tires. Around town, I only seem to get about 16mpg. All in all, not bad.

Thanks again for your efforts to enlighten us all!

 

[03_4x4Runner]

You would get run over on the interstates in Arizona going 65. The speed limit is 75. In west Texas it is 80 mph on the interstates. I have a similar lift and all terrains. Before the the lift and tires I got my best mpg on interstates, after the lift and tires this is where I get the least mpg. Agreed back roads at 55-65 is best for me now.

 

[chaz]

nice test showing what even a 5 mph difference can make in mpg.

 

[CookieRoe]

Thanks for sharing! I wonder if these "gains" can be had with the V6. Probably considering the V8 and V6 have the same tranny.

 

[Milam]

I just recorded my lowest MPG this past fill up (15.6 mpg) with most of it being hwy. I usally drive around 70 mph on the highway.

 

[eskim0chaos]

I get 13 going 85. I like it.

 

[12guns]

14.2 @ 70 mph sounds pretty low to me. I have FJ springs w/ Bilstein's and have about the same lift as you. I even have a Yakima "low rider" rack and can get calculated 17 mpg w/ the cruise set on 70 and a negligent amount of in town driving. I also have a K&N drop in filter and 6 ply aftermarket tires which will be similar to yours. Not sure if the filter would help or hurt. Have you cleaned the MAF? New air filter and such?

I'll get more like 14 if I'm pushing 80 and driving like a bat out of hell...which I'll admit happens from time to time.

You're right in saying slowing down makes a huge difference for our V8's!

 

[ThreeFiveO]

That's quite a difference in mileage.
One of my few complaints about the v8 is full-time 4WD, think how much better the mileage would be if you weren't always running in 4H.

 

[DocMT]

You can't judge fuel economy by a single trip. Too many variables. I went on a ski trip recently that was a bit more than 500 miles each way. On the way there, I was driving easy and maintaining a steady 65 MPH pretty much the whole time. I calculated my fuel economy at 18 MPG for the trip there. On the way back, I didn't care about trying to get my best fuel economy, so I was driving more erratically, flooring the gas pedal to pass people etc... When I calculated my gas mileage, I was surprised that it was almost 20 MPG. I think maybe I had a tailwind on the drive home and that's the reason for the better fuel economy. The way I was driving, it certainly should have been much worse.

Anyway, the point is that a single trip is a poor indicator to say that there's a big difference between driving 65 and 70 MPH because there are other factors at play.

 

[12guns]

You can't judge fuel economy by a single trip. Too many variables. I went on a ski trip recently that was a bit more than 500 miles each way. On the way there, I was driving easy and maintaining a steady 65 MPH pretty much the whole time. I calculated my fuel economy at 18 MPG for the trip there. On the way back, I didn't care about trying to get my best fuel economy, so I was driving more erratically, flooring the gas pedal to pass people etc... When I calculated my gas mileage, I was surprised that it was almost 20 MPG. I think maybe I had a tailwind on the drive home and that's the reason for the better fuel economy. The way I was driving, it certainly should have been much worse.

Anyway, the point is that a single trip is a poor indicator to say that there's a big difference between driving 65 and 70 MPH because there are other factors at play.

Good point, even filling up at different stations makes a HUGE difference. Ethenol vs. no ethenol, and so on. I can agree w/ the OP that slowing down below 70 makes a drastic difference for our V8's. I used to drive 80 everywhere I went, but to get another 3 mpg I'll gladly slow down to 70!

 

[JB.]

~120 miles @ 70 MPH: 14.2 MPG
~120 miles @ 65 MPH: 17.1 MPG

Thanks for posting the results. I think the out and back comparison makes it a little problematic. Comparing two loops would be a little more reliable but even there, wind can mess up the numbers. The good news is, the number that seems most likely to be skewed is the 14mpg. You should be able to get 17mpg at 65mph no problem.

 

[thirstyturtle]

14.2 @ 70 mph sounds pretty low to me. I have FJ springs w/ Bilstein's and have about the same lift as you. I even have a Yakima "low rider" rack and can get calculated 17 mpg w/ the cruise set on 70 and a negligent amount of in town driving. I also have a K&N drop in filter and 6 ply aftermarket tires which will be similar to yours. Not sure if the filter would help or hurt. Have you cleaned the MAF? New air filter and such?

I'll get more like 14 if I'm pushing 80 and driving like a bat out of hell...which I'll admit happens from time to time.

You're right in saying slowing down makes a huge difference for our V8's!

The filter was replaced when I bought the vehicle 8,000 miles ago, still looks great to me. Haven't cleaned the MAF sensor, wasn't aware it needed to be cleaned. How would I go about doing this? Slash, where is it? In the intake duct after the filter I assume?

Sent from my ADR6300 using Tapatalk

 

[Trevloc]

i got 17.8 mpg when coming back from cali in high winds, going 83 set with cruise control.

 

[12guns]

The filter was replaced when I bought the vehicle 8,000 miles ago, still looks great to me. Haven't cleaned the MAF sensor, wasn't aware it needed to be cleaned. How would I go about doing this? Slash, where is it? In the intake duct after the filter I assume?

Sent from my ADR6300 using Tapatalk

Cleaning the FAF airflow sensor is not always a quick fix, but for a $5 can of cleaner from autozone, it's worth a shot! Search and you'll find more, but in a nut shell, it's a small box looking thing that is just upstream on between your airbox and throttle body. It will have two screws holding it in, just unscrew, unplug from the wires, and you'll be able to spray some cleaner (do not touch or scrub) you're just cleaning the small wires you can see w/ the spray cleaner. Reinstall and you're done. Probably about time to change our your air filter anyway. Even if you can't see any dirt, it still gets clogged up and can restrict airflow. Hope that helps!

 

[JohnsD90]

Shut the cruise control off and you will really be getting good mpg.

 

[thirstyturtle]

i got 17.8 mpg when coming back from cali in high winds, going 83 set with cruise control.

That's awesome man!!!

I was just trying to make a point that a slower speed (at least for me) provided much better fuel economy.

Thanks for all the comments everyone!

 

[Nuke]

I do quite a bit of long range (400+ miles one way) in different speed zones and the change in fuel consumption at 5 MPH intervals is pretty astounding.

Hand calculated, here are my typical averages:

75 MPH - 19 mpg
70 MPH - 20 mpg
65 MPH - 23 mpg
60 MPH - 25 mpg


I did a few less-than-200 mile stretches at 55 MPH mixed with higher speeds over the rest of the tank and I suspect at 55 MPH I was averaging 26-27 mpg.

 

[Nuke]

Shut the cruise control off and you will really be getting good mpg.

True if you're in hilly terrain and the tranny keeps downshifting to maintain speed. I've you have a "talented foot", you can leave cruise on and take manual control of the accelerator before the valley to reduce the downshifting.

 

[KB084RUNNER]

I do quite a bit of long range (400+ miles one way) in different speed zones and the change in fuel consumption at 5 MPH intervals is pretty astounding.

Hand calculated, here are my typical averages:

75 MPH - 19 mpg
70 MPH - 20 mpg
65 MPH - 23 mpg
60 MPH - 25 mpg


I did a few less-than-200 mile stretches at 55 MPH mixed with higher speeds over the rest of the tank and I suspect at 55 MPH I was averaging 26-27 mpg.

+1 I get over 20mpg at 65 easily.