As the owner of a big heavy truck that likes to drink up a lot of gas I find myself being more and more conscious about saving gas. I do like driving my truck a lot, but I don't like the gas prices hitting my wallet like they do. Here are some general rules (that are common sense) that I do to improve my mileage. By the way, I always hand calculate my mileage. The overhead is a good indicator of when your mileage goes up or down, but I've found in the 3 3rd gen trucks that I've owned it's almost always 2-4 mpg higher than actual hand calculated mileage.
1. Wide Open Throttle (WOT) matters: As a rule, When you hit the gas to accelerate hard you are using more gas. This hits drivers every day when they accelerate. If you have a heavy foot and mash the gas when accelerating you run the RPMs up high wasting gas. If you accelerate more slowly your RPMs stay lower saving you gas. Keeping your RPMs below 2k at
all times can save you 1-2 mpg every tank.
2. The sweet spot: Every engine has a sweet spot in the RPM range where it is operating at peak efficiency. You need to find the power curve for your engine and find where the torque starts to drop off (the graph below shows the drop off at around 1800 RPMs). This number is where you want your engine to run most of the time. You can try to optimize (taller tires, different gears...) your vehicle so that when driving your engine runs at this RPM most of the time (the new CVT transmissions try to do this). Unfortunately this quite often only works for diesel engines. The graph below shows the power curve for the new
Cummins engine that will be going into 2010 dodge vehicles.
Unfortunately most of us drive around in vehicles with gas engines that don't produce maximum torque until over the 4k mark. By the time the engine gets to that range any savings in gas is eaten up by increased wind resistance, heat, and friction in the engine. You can do other things though, to get closer to that number, you can get new gears for your vehicle or turn off overdrive for example. Buying shorter tires would help as well. To find out what your rpms would be with different gearing/tire combos you can go to
www.moparregister.com/calc.php3. Weight: For every 100 lbs your fuel efficiency goes down by 2%. An easy way to reduce weight is to remove that set of free weights you carry around in the bed to so that you know your truck is always carrying a load. Another way to reduce weight is to remove the tailgate in favor of a net or nothing (this hurts your aerodynamics though). You could also lose that spare tire (what are the chances that your 31" spare will work with you set of 35" all terrains that you just bought). You can make sure to only fill up half a tank, these trucks still get around 400 miles per tank so you would just fill up half the tank every 200 miles. Remove anything you don't deem necessary for the use of the truck on a day to day basis.
4. Tire pressure: I know, it's really easy to check your tire pressure once a month. If it's so easy why haven't you ever checked your tire pressure? Tire pressure gauges are cheap and if you can't read a slide with numbers on it there are plenty of digital ones out there. Air for your tires is free at half the gas stations out there and it's only a quarter at the other half. Letting your tires get low on pressure can reduce your mileage by 5% or more. Note: you'll want to check the tire pressure before you drive your car, if you do so after just driving your vehicle the pressure will be artificially inflated due to all the heat put on the tires because of rolling resistance. Also make sure to check the pressure more often in the winter. Rolling resistance can be a drain on mileage as well. You can go
here for more information about rolling resistance and tires.
5. Mods: As a general rule, the more HP that the engine is rated for the worse your mileage will be. You can still go out and get the hemi, just be ready for 11 mpg (city) to suck some extra cash out of your wallet. You can also do a number of performance modifications mileage up. You can get a new cold air intake and exhaust system. You can get an electric fan. You can get a supercharger for your engine. Most modifications that increase HP will net you a small gain in mpg. When all added up you can see some good gains, just be prepared to shell out a good amount of $$ to get this done. So you can go out and get the 4.7L engine with 310 HP and mod it up to 345 that the current hemi has stock (you can also fill up with E85). But you won't ever be as fast as a hemi with the same mods as you.
Special note for Hemi MDS owners: you can make the engine run in 4 cylinder mode a lot more often by reducing the load on the engine. This is done most easily by switching from your 3.55 or 3.92 gears to 4.56 gears and reducing weight/improving aerodynamics. By switching to the higher gears the engine runs higher RPMs (about 300 higher depending on tire height) but it will run those RPMs in 4 cylinder mode a lot more often because the new gears make it easier for the engine to turn the tires.
6. Aerodynamics: the more easy it is for air to get around your vehicle the less gas you use to push your vehicle through the air. Sure those monster trucks look like they could eat your truck for breakfast, but the only thing they're eating is more fuel to get where they're going. Reducing drag on your vehicle is key. Auto makers already know how to reduce drag, they just need the incentive (pressure for better mileage) to do this. The 09 Ram was designed with aerodynamics in mind, the new Ram will get 10-15% better mpgs just from improved aerodynamics. Also, drive with the tailgate up, this creates a cushion of air that sits in the bed and other air flows pretty well over it.
Anything that can be done to reduce the grip that air has on the vehicle helps as well. The cab extension on the Chevy Avalanche performs this task to a degree, but there are other things you can do. In '06 dodge introduced a spoiler that attaches to the tailgate of the truck (only on 1500 short box frames) that helps to break up the air behind the truck. The spoiler for the SRT 10 also creates a kind of tornado behind the truck so that air moves beyond the truck more freely.
Lowering your truck also reduces the aerodynamic drag. Taller tires and lift kits create a lot of extra drag. Many trucks these days come with an air dam up front under the bumper as well as inserts that close up any holes between the bumper and the body.
7. Buy in the morning: Gas, like anything, expands when warm. It's cooler in the morning so you'll get more gas per dollar than in the afternoon.
8. Synthetic: Most people note a small increase in mpg when they switch to synthetic oil. I know synthetic costs more but you also go longer between oil changes and there is less wear and tear on the engine.
9. Sweat: If you don't mind being uncomfortable and dehydrated you can opt to not use air conditioning on warm days. Using air conditioning can easily sap 1-2 mpg.
10. Cruise: If you're like me and you daydream most of your driving away you'll also vary speeds a lot. I should note that doing this usually angers the line of cars behind you and inspires creative hand gestures as people pass you. Varying speeds on the highway uses more gas than just sticking to a constant speed (picking a slow constant speed also angers other drivers) so use cruise control.
11. Beater: If you're already doing all of these things your last resort might be to swallow your pride and buy that geo metro that gets 48 mpg and fits into the bed of your truck. If you drive a number of miles each day and you can make the initial cost of the car low the savings in gas will pay for itself. And unless you're Andre the Giant you will find that most of these economy cars have plenty of room for you.
