Horrible gas mileage

Hello, I have a
2008 Tacoma long bed V6 4.0L with 33inch tires (189,000) and I’ve always been able to get 15mpg city and around 17 hwy(Even with the 33’s!)
Ever since I installed this camper shell(are series) I am now getting 10mpg and 12 hwy.
I have tried the following:
Tire pressure all around 29psi
Clean air filter
Fresh spark plugs
Just cleaned MAF sensor (no difference)

I am not sure what else to do and was wondering if anyone would be so kind do suggest some tips.

Adding a camper shell shouldn’t decrease it that bad (or maybe I’m wrong)

On a full tank(21.1) gallons, I can go only 230 miles. And that’s mostly highway driving and keeping the rpms lowwwww

It’s getting expensive with $4/gallon gas prices

 

Shell disrupts airflow and reduces MPG.

29 psi is low as shit.

You added 150+ lbs of weight to your vehicle and that doesn’t help either.

33s aren’t for mileage.

 

Have you always ran 29psi? Sounds a little low to me, I run 34psi on my 265/75r16. I noticed no difference in mpg when installing my high top shell... or atleast the shell didn’t decrease enough to affect me like that. Maybe 1 mpg less at most.

 

My canopy has never effected my mileage either. I agree that the 29 psi is low, especially in the winter time. Could just be the change to winter gas in your area. I’d reset your computer, let it learn for a tank of gas, and then re check your mileage manually.

 

I'm getting 13.9 mpg freeway with 305/70R16s, front Bilstein 5100s, and a leer camper shell. 5 mpg less than stock. It's pretty terrible but I just stopped paying attention to how many miles per tank I get and know that I'll just need to fill up twice a week now. $400 a month roughly unless I get stuck at work...

 

15-17 then added a shell and 10-12.
Tires and pressure same before and after, even while maybe low, did not change.
What else did you do around the same time as this does not add up.
Shell as others said maybe 1-2 decrease at most.
189k miles so how are all the wheel bearings and rear diff as mine all went at 100k and a major drag/mileage reducer.

 

Is your odometer correctly calibrated? Changing tire size throws it all off. Types of tires, width, gearing,weight,etc...

 

Camper shells usually aren't much trouble to install & remove. Would it be feasible to remove it & run a tank of gas, if mpg. goes back up, that's the problem, if not, look for something else.

 

@muddog321
I replaced the front wheel bearings about 4 months ago. (Didn’t buy the ones you press in I got the whole hub assembly)
And I changed my CSB & U joints as well as a driveshaft balance.
However for the 100,000 miles I’ve owned the truck I haven’t touched the rear diff fluid yet.

 

I'd do both diffs if you're 4x4, and your transmission fluid if you're a 6 speed.

Not sure what the maintenance interval is supposed to be for the auto transmissions, but it's recommended to replace the front and rear differential fluids around 65k miles if I remember correctly. That's when I did mine. 100k miles seems like wayyyy too long to go without changing diff fluids.

 

@Ccrames2018
Thank you for the tip
It’s 2wd, I’m gonna add it to my to-do list for this week

For the trans, fluid was changed about 20,000 miles ago however I didn’t use “WS” fluid, I used Valvoline ATF but I really need to change it again so I can get the right fluid

 

Yeah it's fairly cheap to do the diff fluid, and just follow the owner's manual for the tranny fluid. Good luck!

 

My cap adds 180 lbs to curb weight, but it also makes the truck more aerodynamic. If anything my fuel mileage improved with the cap. I ran just under 40 PSI with P series tires, closer to 35 PSI with LT's. I get 20 mpg hwy, 16ish for normal every day driving with 31.5" Lt265/75/16 tires on my 07 4X4.

29 PSI is OK for off road driving, but way low for every day use.

 

Are you taking into account that your odometer is no longer accurate with 33s ... so the M in your mpg calculation is going to be off.

 

If you used Maxlife, you're fine. Everybody uses it.

 

Back to the orig. post, "ever since I installed the camper shell". He said nothing about lost mpg. after installing 33" tires. He never mentioned lowering the air pressure to 29 psi., probably been like that all the time. Surely the trans. fluid & diff. fluid didn't go bad right when he installed the camper shell. If wheel bearings are bad enough to lose 30% of your fuel mi., you will know it pretty quick, with that much drag, the heat in the bearing will probably melt the hub, before a tank of fuel. Just a fact, a faulty oxygen sensor can cause a drastic loss of mpg. Most local parts store should check that for you free, but the odds are against an oxygen sensor going bad right when you install a camper shell. I agree, installing the camper shell shouldn't effect the mpg. that much, but to be sure, remove it & run a tank or two of gas, to see if mpg. goes back up. Good luck, & let us know what you figured out.

 

I run 35PSI. 29 sounds low. The camper shell, 33s, winter gas, winter driving conditions and winter warm up times are all mileage killers.

 

I had never thought about the winter blend fuel. Maybe that's why my MPG seems to be about 1 MPG lower than usual. I'm only getting 14 with my camper and 305s.

 

Odometer would still be accurate regardless of tire size since it gets its input from the vehicle speed sensor and/or turbine speed sensor inside the transmission, whereas the speedometer gets its information from the wheel speed sensors (and hydraulic brake booster). The transmission rotates based on engine RPMs (throttle inputs, etc..) and is independent upon wheel size, mainly getting its input off of engine load. The wheel speed sensors on all 4 wheel hubs will change depending on how fast the tire is rotating based on size/diameter which is why it is suggested to get a calibrator to "fix" the signal and give you a more accurate reading on your speedometer. I run the Hypertech Inline Calibrator which intercepts the wrong speed signal and does the math for be before sending it to the speedometer. Others have used a Scangauge to do this so you'll have some options.

-J

 

You really shouldn’t post before you drink your coffee.