What caused my sudden increase in MPG?

[wicked1]

This is a somewhat strange situation.. My MPG has increased 1.5x or more. I have a 2012 Tacoma. Four Wheel Camper flatbed camper on the back.. I don't have an instant MPG readout, so calculate it by tank of gas.
I have always gotten 10 MPG. Sometimes a little less, sometimes a little more, but right around 10. I took a trip this past weekend, and got....... ~16MPG! All 4 fillups.

The things I've changed..
New spark plugs. But the truck had new plugs when I bought it a few years ago, and it got 10mpg then.
New suspension. I had some SUPER STIFF suspension, which I replaced w/ a tuned fox setup. The ride is much better, but I don't see how this could have affected MPG.
I replaced my 140 weight differential fluid w/ 110 weight. Aftermarket gears always suggest 140, and I know that's what the previous owner had. That's what I put back in it when I installed my locker. But this time I went for 110 synthetic. I could see this making a technical difference, but wouldn't expect it would be enough to notice..

And.......... I had 3 bikes mounted to the back of the camper. My current theory is that the bikes are breaking up the aerodynamic drag which happens behind big flat vehicles.. I don't see how any of the truck maintenance or suspension could do it.. but I could be wrong, which is why I mentioned all the recent changes.

What do you think caused the change??

It was amazing when we noticed it. All of a sudden my wife yells, OMG we've been on the road for four hours, are we out of gas?!? and I look and am like.... Huh.. No, we've got 1/2 a tank! We have never been able to drive longer than 3 hours... It's amazing!

 

[wicked1]

Yeah.. I'm definitely not complaining. I want to go on a long trip now!
I guess I need to drive it w/out the bikes to see if that is what's doing it. But, that requires a long drive on the highway to duplicate the situation. Would be easier if I had an MPG display!
It's such a big difference... If it's the bikes, it would be good to know people can maybe add something to the backs of their campers, and we'll solve the worlds energy problems, heh.. I'll eventually do the no-bikes test.. But the next few trips are bike trips, so it might be a while before I figure this out.

 

[skrypj]

Did you have a tailwind? I have seen anywhere from 6.7 to 11.1 towing my travel trailer depending on conditions. 95% of the time i seem to get a headwind for some reason so getting over 10 is a very rare situation.

 

[wicked1]

Did you have a tailwind? I have seen anywhere from 6.7 to 11.1 towing my travel trailer depending on conditions. 95% of the time i seem to get a headwind for some reason so getting over 10 is a very rare situation.

I wouldn't expect it, but I suppose it's possible. It was all four fillups on this trip, regardless of direction.. I need more data before I can be sure this is a permanent change, I guess. But it is the first time I've ever seen more than 11mpg.

I guess a cumulative change is possible, where each change I made to the truck over the past couple months added a little. But I'd honestly not expect the changes to affect MPG at all, and I'd expect the bikes to make it worse.
But this actually happened.. I sometimes exaggerate to make a story better or something, but this is 100% accurate. I went from 10mpg on average (usually see between 9-11).. Which I was definitely getting in June. Then I made these changes to the truck over the summer. I had the bikes on the back for the first long trip w/ them. And I got 16mpg on every tank.

-edit to mention, along w/ the new suspension, I lowered the front by about 1/2".. My truck was about 3" over factory, which was a bit excessive. This new suspension is adustable, so I lowered it 1/2" from where it was. Which is another change I'd not really expect to be enough to make any difference. But is a change that happened.

 

[rruff]

This is a somewhat strange situation.. My MPG has increased 1.5x or more. I have a 2012 Tacoma. Four Wheel Camper flatbed camper on the back.. I don't have an instant MPG readout, so calculate it by tank of gas.
I have always gotten 10 MPG. Sometimes a little less, sometimes a little more, but right around 10. I took a trip this past weekend, and got....... ~16MPG! All 4 fillups.

16 is good for your rig.... and 10mpg is atrocious! I got a hair over 16 a couple weeks ago in my Tundra with a big stand-up camper, 35s, and 2" front lift, not wind aided, 4k to 8k ft elevation. Previously on the same route I averaged 17.7 mpg with no camper, so it is lower. Long out-back trip, ~1/2 freeway, and 1/2 secondary, with lots of elevation change.

Rolling resistance of tires can vary a lot. Did you change those? Other things that can make a difference: wind, speed, hills, elevation, etc.

I kinda think your engine is running good now, while it wasn't before.

 

[MR E30]

I am in a similar situation to you, and I also carry bikes on the back of my truck permanently now. They are rack based from the hitch, and there are two of them.

I have noticed no difference in tank mpg's with the bikes added to the back. I am a bit familiar with the suction effect of the air that can occur at the rear end of rectangular vehicles, but I don't know if it can cause the dramatic increase that you saw. I doubt that it can, on its own.

I get ~10 mpg when aired down offroad (16 psi is my comfort zone) and ~17 on average when on paved roads (max speed is 65, and I often do 55 if I am on smaller, less traveled highways).

The best I have ever seen is ~25 mpg on a third tank of gas, but that was a highway based route that was almost entirely downhill. Must have also had a decent tailwind that day too, because those kinds of mpg's shouldn't occur with my truck.

I did notice a ~1 mpg increase when I went from 140 weight diff fluid back down to 90 weight after my 500 mile check, and I have heard that others noticed similar changes as well.

Picture of my setup for comparison:

Week of 9/25 - Home by Michael Rickerd, on Flickr

I'd keep paying attention to try and figure it out. That kind of jump can result in saving some serious money on longer trips!

 

[NatersXJ6]

When I was in college, we may have participated in a prank that involved adding gas to a room mates car every night when he thought his new “tornado” would add mileage.

You might want to watch your “friends” closely.

 

[wrekreate]

When I was in college, we may have participated in a prank that involved adding gas to a room mates car every night when he thought his new “tornado” would add mileage.

You might want to watch your “friends” closely.

I need to find me some friends like you!

 

[Joe917]

Faulty fuel flow sensor?

 

[NatersXJ6]

It was a much better prank at $1.25 / gallon!

I’m not sure I could do it at $5.50!

 

[grizzlypath]

Were you driving south? Going downhill slightly would have probably helped.

 

[BoostTed]

Old thread but where do you live? Maybe your local gas stations switched to the winter blend of gas. Winter blend has less ethanol?

 

[Wisconsinite762]

Old thread but where do you live? Maybe your local gas stations switched to the winter blend of gas. Winter blend has less ethanol?

Winter gas blend is worse, you get less mpg with it. Though it is technically only ~2% less energy dense than summer blend. Not a huge difference.

 

[MontySquareo]

Did you change tire psi at all? My guess is lowering the front kept your truck from trapping as much air underneath and the softer suspension could have something to do with it but that seems unlikely

 

[Wisconsinite762]

Did you get an alignment with the new suspension? If your previous alignment was bad I could see that causing increased fuel consumption. Plus maybe the couple other things cumulatively helping you out.