Road Trips and Gas Mileage

[RochesterMJ]

Took the MJ on a road trip from the Detroit area to South Dakota's Black Hills and back.  2970 miles total.  Left last Wednesday and got back late Monday night.  Truck was great, had no problems and was surprisingly comfortable.  

 

Typical speeds of 75mph using 87 octane, averaged 16.2mpg for the whole trip.  Counterintuitively, the few times I had to buy gas with ethanol (87 with 10% and 88 with 10%) my mileage actually rose to 17.7 and 17.2!?!  I'll have to go back and try to figure out if there were other differences (terrain, speed, ...) but until then what are your experiences with ethanol gas?  

 

 

Truck is 4.0L, AW4, 3.55, D35, D30, 3" lift, 31" All-Terrains.

 

[Randy in Maine]

Did you account for the taller tires?

 

I use 10% ethanol all of the time, but only drive about 65. 

 

I get 21 usually and almost see 22 mpg some of the time.

 

These things are amazingly comfortable tooling down the road.

[RochesterMJ]

Same tires throughout the trip.  

 

You get 21 with a 4.0?  Stick or auto?

[Randy in Maine]

Those taller than stock tires are throwing off your odometer.  Most 31x10.5x15 tires turn about 678 revs per mile (outside circumfrence is about 93.45").  The stock size is 205/75/15 and turns about 766 revs per mile (outside circumfrence is about 82.72").  The change is about 1.129.

 

So your actual trip was likely closer to 3353 miles and you probably got closer to 18.3 mpg when you do the math.

 

I have a 5 speed 4.0 and turn about 2050 RPM doing about 65 mph when I had stock tires.  My MJ just likes to run at 65 most of the time.  I am OK with that.

[Roost426]

Fromy my calculation's I have been steadily getting about 19-20 mpg, this is mostly driving around backroads 40-55mph and some city driving. I am running 235/75/15's and have a pretty bad exhaust manifold leak at the moment so not sure how those are affecting thiings. My truck does not like to pull 5th gear until 45mph, seems to boggy below that.

[RochesterMJ]

Thats a great reply Randy, thanks.  

 

I did swap out the speedo gear per the PATC calculator, that should have compensated for the taller tires.  Noticed on the trip that my GPS and speedometer aren't in agreement.  Maybe I'll pop the old gear back in and see if its more coordinated with the gps.  

 

I'm thinking now that the higher mileage was a result of lower average speeds for those tanks (65 instead of 75).  

 

Hope you guys had a great Christmas

[benjy_26]

I usually do about 60mph on the highway with my 4 speed 2.5 on 31" AT/KO's and I get between 23-25mpg depending on how hilly the terrain is. I pump 87 octane with a claimed 10% ethanol mix and I monitor my speed via GPS.

[benjy_26]

Oh, and if I have to do a lot of stop and go driving, my mileage SINKS. I have to be very aggressive in city driving in my area. People will run over you otherwise!

[Randy in Maine]

Of course the big thing is also that I am running the stock gearing (~ 3.08) and the slower speed.  I am not sure how much not having a lift kit helps me gas mileage wise.  I don't have cruise conrol although I wish I did.

[Dirteatr717]

Moved from Long Island NY to Park City Utah totaling 2,461 miles with the bed completely full of my belongings in September, I cruised between 65-70 the entire trip and averaged 18 mpgs somehow.. 4.0,5spd with 4.10s and 35" KM2s, also have a large crack at the usual spot on the exhaust manifold.

[johnj92131]

Speed makes a big difference in mpg.  If I run at 75+ mph, then 16-19 mpg is reasonable.  Keep it to 55/60 and I can hit 23+mpg.  But who can drive 55 mph on an interstate?  But, I did not get the truck for fuel economy.  When I want an economical trip, I take the Passat TDI and plan on 45-50 mpg.  Even the Camry will get 30+ on a road trip, 32 at 70/75 and upwards of 37 mpg at slower speeds.