GAS MILEAGE GONE
This July I had a lift kit installed, along with rims, tires, Airaid intake and spacer and an Air Lift system on my 2001 Dodge Dakota Club Cab 4x4 with a 4.7L V8. I went to a 3-inch Rancho kit with shocks and went from a 31x 10.50R-15 AT tire to a 265/75R-16 BFG AT on ProComp 8089 wheels. I was never so happy to get my truck back looking so great! In August, I towed a heavy trailer to Florida but I was only averaging 120-150 miles per tank, 6-9 mpg on average. I was getting about 300 miles per tank empty and now I'm getting an average of about 200-230 miles per thank. The dealer has no clue to what's happening. Is the tire size or the weight of the tires and rims causing it? Is the stock gearing off now? I was told that the intake mods would make performance better. So what gives?
Greg Hobbs
First off, let's pretty much ignore the towing mileage. What you listed sounds fairly typical. I guess it depends on what you mean by a "heavy trailer." The drop in solo mpg is more disconcerting. By my estimates, you were getting about 18 hwy mpg before and you have dropped to about 13. Larger tires and lifts cost mpg due to the loss of aerodynamics and increased rolling resistance. No way around it and not much you can do to get it back, but your drop is more than I would have expected. You gained something over an inch on your tire size... not a huge change. It does change the overall gear ratio but there's enough flexibility in your truck to soak up that much difference, especially on the highway. My books say your truck came standard with 3.55:1 gears and 3.92s were optional. A 265/70R-16 was the largest optional tire and that was about the same height as the 31s you had and extra inch shouldn't make a huge difference in actual performance and mileage. One thing that comes to mind is whether you have had your speedo recalibrated. A taller tire will cause an uncorrected odometer to read fewer miles, thus indicating worse mpg. A dealership can reflash your computer to match the tire size, but they may not want to. Another option, if you are interested in a chip, is to buy a programmer that offers the option to calibrate for tire size changes. The Hypertech products come to mind (www.hypertech.com) because I recently fooled around with some of them. You can gain a little power and recalibrate at the same time. If your computer has been reflashed for the tire size change, then I cannot account for the extreme loss. I could understand a 1-2 mpg loss in your circumstance, but not 5 mpg. Unless you moved to Flagstaff, that is. Altitude might cost you another 1-2 mpg off sea level specs.
NO GUTS, NO GLORY
I recently found a '95 Ford F-150 with 90K miles, 5.0EFI and AOD. It has a 3.55 limited slip and HD suspension. The truck is in excellent condition from the original owner. My only complaint is that it has very little low end torque. I would rather have "guts" than high hp. I'm looking for recommendations as to what I can do, perhaps in priority order, as to "bang for buck." My thoughts include a free flow cat and muffler and a single 3-inch system. Possibly shorty headers. On the intake a K&N type filter. Being at 5000 feet with trips to higher mountains, I was also thinking about advancing the timing from 10BTC to 14. What thoughts do you have?
Ken
Think gearing, Ken. Gearing is a torque multiplier. The stuff you mentioned will not add substantially to low end torque from the engine. More so midrange and upper end. If you were to change the axle ratios from 3.55:1 to 4.10:1 you will increase the amount of torque going to the ground by about 16 percent. In essence, your engine's 270 lbs-ft is multiplied 3.55 times now (958.5 lbs-ft at the ground in direct). By changing gears, it's being multiplied 4.10 times (1,107 lbs-ft in direct). In essence you gain 198.5 lbs-ft at the ground. Getting 16 percent from any mods on the engine would be costly and not give you the boost the gear will. Given your altitude and the amount of power you've already lost there, it limits the gains you'll get from engine mods as well and the gearing change makes even more sense. As to the other stuff, I'd go with a cat back and a free flow filter first. If you can bump the timing on your truck, it would be a good idea, but consult your manual on exactly how to do it.
“EX-POST-FACTO-STICK-IN-THE-MUD”
I recently went off-roading in my 2005 Jeep Wrangler and got stuck in the mud. I was deep in mud. I don't know how I got out but I got out myself! Now everything has changed. It seems to run a little hotter than before and the check engine light came on. The light went out after two days but it seems to be getting hotter at stops in traffic.
Jose Cubillo
A coupla things come to mind, Jose. First is that your radiator is full of mud. If there's mud packed into the fins and tubes, there's no airflow and it's like a blanket over your radiator. A handful of quarters at the carwash, or a little time with your pressure washer at home. Will blast that stuff clear. The second idea is that you may have damaged the fan or fan clutch. That happens in the deep stuff sometimes. The check engine light might be related or not. The way to tell is to get a code reader and find out what code pops up. Simple code readers are inexpensive and available at most auto parts stores and even many large department stores, like K-Mart . Also, some auto parts stores will rent them to you. I've even seen some of the friendlier ones even come out to do the check for someone (not that it's hard!).
POWER WAGON LOCKER LOCKOUT
I was reading the Gearhead column in the February ’07 issue when I came across “Power Wagon Cog Query” where you stated the only problem you knew was not being able to use the lockers in high range. I have an ’05 Power Wagon and feel the same way. I know people have wired a bypass switch around the transfer case position sensor and wonder if the same thing can be done with a Power Wagon? I pulled a diagram off the internet and it looks like the bypass would work. Any thoughts? Do you foresee any problems with this modification?
Dan Brown
Dan sent me a copy of the diagram and it appears to match what I found in a manual at my local Dodge dealer. If you wire a switch in between the wire going to and from the t-case sensor, it fools the computer into thinking the tcase is in low range. Based on what I saw, I don’t see why it won’t work as it does with the Rubie. All that’s required is for the operator to have the grey matter to know when and where to use the modification... just as it would be if you had taken a regular Dodge Ram and installed ARB Air Lockers front and rear.
FORDOTA AXLES
I have a ’92 Toyota standard cab pickup with a 6-inch lift. I am in the process of putting a Ford 302 motor in it with a T-18 transmission. What kind of straight axles do you recommend for the front and rear?
Mario
That depends on how big a tire you plan on using and how and where you drive. The factory Toyota axles are reasonably stout. Unless you plan on going bigger than 35 inches, or you are a hard core rockcrawler, I think the current rear axle could stay. From there, I’d try getting a ’79-85 Toyota solid front axle to match. There are upgrades available for both axles to make them stouter if needed. If you are going significantly bigger than 35s and plan to work your rig hard, start saving for a pair of Dana 60s.
SUCKY SUPER CREW ECONOMY
I drive an ’03 Super Crew 5.4L with 4.56 gears, 315/75R-16 tires, K&N air filter, Flowmaster exhaust and a Hypertech programmer. After all of these mods I still can’t get more than 11.5 mpg on average. Sometimes I notice that after releasing the brakes the truck still feels held back. After all these mods to help with fuel economy and power loss, why am I still getting sucky mileage? Is this normal or can there be a problem somewhere else?
J. Flores South Gate, CA
An average of 11.5 mpg with a lifted
crewcab with fat tires weighing over
6,300 pounds is pretty good. If you
commute in SoCal traffic, it’s especially
good. You may want more of
course, and for that I’d look to your
right foot and always travel as light as
possible. With a truck like yours, I
doubt you’ll see much over 12-13 on
average in commuter traffic no matter
what you do. Perhaps you might get
into the mid ‘teens at a steady freeway
cruise. To check your brakes, I’d get
them good and warm, then jack the
truck onto stands, have someone
apply the brakes, then release. Then
you go around and see if all the
wheels spin freely. A sticking caliper
will often show up via abnormally
worn pads on one wheel.