My truck gets between 14 and 16 mpg when driving to and from work. I drove from Yuma to Phoenix and only got 17 mpg while running between 70 and 75 mph. I have 4.10 gears. What gives? I thought I was supposed to get at least 20 if I was getting 14-16 in town.

 

4X4 and 4.10s - that is the culprit. Add in 70 to 75 and you drop mileage due to wind resistance.

For example - 75 mph running I-95 Raleigh to Orlando (flat and straight) with AC on was 20.9 mpg last week.

This weekend I filled up outside of Martinsville, Va and proceeded to cruise the backroads up to the Blue Ridge Parkway (stopped at my folks house for the evening) then down the Parkway at 45 mph with OD off to I-77, down I-77 to I-40 to US 64, then down US64 to Lake Lure. The road to Lake Lure reminds me of the road around Lake Tahoe, 25 mph is pushing it and you get to see your own taillights on the curves. Stayed at Lake Lure, puttered around a bit then left for home. When I filled up outside of Burlington I had clocked 447 miles on 19.9 gallons, correct for the 2% error due to taller tires and I got 22.9 mpg. Half of that was 45 mph on curvy roads, the other half running 65-70 on the interstate.

The advantage is 3.55s, 2WD, 15.25* timing and driving smoothly in the mountains. I have pulled 26 mpg on this truck in the past with shorter tires and 13* timing so this mileage does not surprise me. These trucks still impress me........

 

BTW - my normal driving around town and 25 mile each way commute mileage runs just under 20 mpg (with a stock slush box). YMMV

 

You're probably at or near optimal mpg for your truck. 4.10 axle, 4x4, ext. cab, and long bed all add weight and height (4x4) to the truck. That means more hp to move the pounds thru the air. The only thing that would make it get worse mpg would be a 3500 dually.

You could probably squeeze out 1-2 mpg with bigger tires. Try 235/85-16's or 265/75-16's which will roll a little (2.5% to 3%) farther with each turn. With the 4.10 axle, your motor will rev a bit lower at 70-75 mph. My truck has 3.54 axle, and gets about 20-21 in 50/50 mixed highway/suburban driving. Empty highway is 22-24 depending on speed, terrain, a/c, etc. Towing 6K highway is about 18-19 (not much air resistance, just weight). Might want to try some more air, fuel plate, GSK, and advance the timing to 15-16 degrees before TDC. Mine had slipped to 10.5, and it helped to put it at 15.5.

 

My normal driving to work 145 mile round trip. M-F between 70 and 85mph I get 21mpg. Worst i've ever gotten was 19

 

with my heavy foot I get 13 in all city driving. Highway is 19, timing advance coming my way soon & it'll make it a tad better

 

Well Im already running 33-12.50-16.5 tires and I did the math for the bigger tires and it came out to 17 mpg. I had plans to do my timing the weekend before the trip but the guy with the tools backed out on me. If diesel continues to be more expensive than regular unleaded then Im getting a bicycle. Filled up in Phoenix on the 14th and it was $2.25 a gallon. It will surely be $3+ before the end of summer. I need all the miles I can for that price.

 

I drive a 1998 2wd 3500 Quad cab 12 valve. It's a Laramie, with automatic, stock size tires (215s), and 4.10 gears.

Around town I typically get anywhere from 17 to 18.5 mpg.

I haven't really had a total highway miles trip yet (I'm the second owner), but I have clocked a tank at 21 mpg.

Modifications: Suncoast converter and valve body. Great stuff and helpful people - call Joe @ Suncoast.
My "tuner" is a very practical guy, who has "finessed" the fuel and boost settings. He advised against fancy airboxes, big exhausts (at least not at my h/p level - which should be around 250 h/p 575 torque), and pushing the timing. I run a stock filter in the factory airbox (some extra inlet holes have been provided) and a Walker 3" racing muffler with no cat. No synthetics.
No "mousemilk", just a well tuned vehicle. His practical side saves wasting money on things that you don't really need.

If I poke on the throttle, I get to powerslide a six wheeled, 7,000 pound truck. If I act like I'm "driving Miss Daisy" then I get the great fuel mileage. What a great truck!

If anyone is interested in my "tuner" and his abilities, please pm me and I will fill you in. Don't expect him to blow smoke up your skirts or to give out free advice. He does his thing to make money, and he knows what he is doing.

Steven B.
Bartlett, TN

 

If it's any consolation, the '95 Chevy K3500, 6.5L HO (High Output ... yeah right!!!) TD, 4wd, crew-cab, SRW, with high-topper, 4.10's & 235/85's I used to own got in the 16's (corrected for larger tire diameter) on the hiway at ~82mph. Actually, it didn't seem to matter how or where I drove it, it ALWAYS got 16's. Kinda strange, but true.

 

4.10's Suck

 

For us 12 valvers, adjust the valves and timing can make a big difference. Also check the overflow valve on the fuel return line.

Just a suggestion. I get 18 to 19 around town, 22 to 24 on the highway and 14 towing 8k lbs.

 

What speed do you have to go to get 22-24 mpg on the highway? On the only road trip I've made so far, I only got 17.5 mpg at 70mph (that put the rpm's right at 2000). That's only slightly better than my regular around town milage...

I'm pretty sure I have 3.55 gears, stock tires, stock auto tranny, and no muffler (just the cat). The truck only has about 40k original miles on it, so I can't believe the timing has already slipped... I've had the valves adjusted, but haven't checked the pump timing yet though.

Do you think that dropping my speed down to 65 would make a big difference?

 

I have to keep my 3.55s under 75 mph to get 22-24. I'm at 2000 rpm at 73 mph.

 

I can go 70 to 75 to get 22 to 24 mpg and I''m at 2000 RPM at @73 also. Going slower will generally help to a point.

65 to 75 mph is the best range for good mpg with the cruz on.

Also, change your fuel filter can help sometimes.

 

cumminsfan
It is quite possible that the original timing was not set properly...giving it a few more degrees will make a big difference.
In addition, check your fuel plate. Mine was installed "cocked" from the factory so that I just didn't have the power that should have been there. More power means better economy, depending on your right foot.