Introduction: Vehicle Efficiency Upgrades: 30+ MPG in 2.5ton Commercial Truck

About: I am an ordinary guy. Except that I live in an RV, drive a 250cc motorcycle, have a truck that runs on bio-diesel, am vegetarian, and have had almost 30 jobs in 10 years, including armored truck driver, bicycl…
[note:  new video has been added on step 1!]
[note 2: Most of what I write isn't relevant to Instructables.  My main blog is here:]

[note 3: Also save energy at home.  See my energy ]

Go 50-100% farther on a tank of fuel.

Due to its size and weight this truck is considered a commercial vehicle and is exempt from even light-truck CAFE standards. Even so, with the modifications I have made, I am getting higher mileage than CAFE standards for 2009 cars.

I read an article in Mother Jones Magazine about Wayne Gerdes, mileage champion, and was inspired. I have read that people tend to get between 10 and 16mpg on average in the same truck I have. I was getting around 15. After the mods described here, on a recent tank I got 30.28mpg.

The best thing to do is to not drive at all. Ride a bike, take the train, carpool.
If you do drive, buy the absolute smallest car you can. If you only need a big vehicle occasionally, rent one.

I bicycle or use my 70mpg 250cc motorcycle for personal transport, but my truck still gets a lot of miles, so I wanted to make it as fuel efficient as possible.
I use this truck for work, moving up to 3 tons of soil or broken concrete, entire 1 bedroom apartments worth of belongings (including furniture) in a single trip, etc.
I also need something with enough power to move my 7500lb RV trailer (which is also my home - a very efficient way to live: I use as much electricity in a month as the average American home uses in one day)

Most of these steps could be done to any vehicle, increasing mileage from 50% to 100% or more.

Step 1: The Cheapest, and Most Important Step

Modify driving habits

Single most significant difference, in any vehicle: "Adjust the nut behind the wheel"
(Drive more efficiently.)

Stay at (or below) the speed limit.
(Remember, you only save 7 seconds per mile going 75mph instead of 65mph, but stopping distance and wind resistance increase exponentially; twice as fast = 4 times the force)
(I have a much more in-depth look at speed at

Accelerate gently (Keep RPMs low whenever possible)

Never accelerate towards a stop light. (Every time you brake you are wasting momentum.  Remember this with the rhyme: "if you have to break, you made a mistake)

Never idle. A popular misconception is that it uses more gas to start than to idle. This was true of older (carbureted) engines. This is not true of modern (fuel injected) engines.

More advanced techniques include actually shutting off the engine and coasting as often as practical. (This can change the feel of the brakes and steering, see step 4)

(PLEASE READ the entire instructable and all the comments before commenting about how dangerous it is to coast.)

NOTE: many automatic transmissions can be damaged by coasting with the engine off.
To find out if yours is one of them, consult this list:
If you have an automatic, and your car is on the list, you can shut the engine while moving.
If it is not, do so at your own risk. You may still benefit from shifting into neutral (engine on) when coasting downhill or towards a stop, depending on whether or not your car has automatic deceleration fuel cut off (DFCI) built in (many newer cars do).

Step 2: Improving Aerodynamics

This is what I did on my 1983 F-250.
Not everything will be directly applicable to your vehicle. Modify and improvise as appropriate.

-I added an underbelly panel to smooth airflow beneath the vehicle made from Coroplast (corrugated plastic - the stuff cheap signs are made from). It is attached to the front bumper, and about 1/2 way back with cut outs for the wheels to turn, and a cut out for oil changes (and to avoid the hot exhaust manifold).  Then there are smaller pieces anywhere a pocket of air could collect, while letting the transaxel and muffler plenty of space.

-I built some homemade wheel "skirts" (wheel-well covers) to improve aerodynamics. The current  are made of cardboard coated in layers of aluminum tape, and then painted and edged with velcro. I lined the wheel well with velcro, and stuck 'em together, then taped over the seams with clear tape to cover the gaps of a less than perfect measuring and cutting job. These were originally just supposed to be a test, but they held up to a winter of rain and months of hauling, so I have no motivation to replace them.

-The headlights come in a little scoop. I had covers custom cut out of thin Lexan plastic, which is totally clear, scratch resistant, flexible, and nearly indestructible (the same stuff my custom motorcycle windshield is made from). I traced the headlights and brought the tracing to Tap plastics who were able to cut them for me in about 5 minutes. I drilled holes in the corners and screwed them onto the grill so I can easily remove them if a headlight burns out.

-I taped over the front turn signals, (because tape is cheaper than Lexan.)

-I removed the windshield wipers (inc. the entire arm). They come off in a few seconds with no tools. I keep them inside the cab, just in case I get caught in unexpected rain.

-I installed a tonneau cover which, in addition to increasing the trucks aerodynamics, will keep small loads clean, dry, and protected, making it a (semi)legitimate business expense.
I cut triangles out of plywood to mount the cover's rails at an angle, so that it tapers down from halfway up the window to the tailgate. 
Having it angled this way makes it much more aerodynamic (I picked up about 1-2mpg just from tilting the cover), but having it go only 1/2 up the cab instead of joing at the top of the roof means I can still see over it and don't lose any visibility to the rear.  It rolls up so I still have full access to the bed when I need it.

Step 3: Disconnecting Extra Engine Loads: Fan, Pump, Alternator, A/c

A surprisingly large amount of the money you put into the gas tank never makes it to the wheels.  I read somewhere that only about 1% of the energy in gas actually goes to moving the driver.  Roughly 1/2 of that energy just goes into turning the engine.  The law of thermodynamics won't let you recover much of that waste, but you can reduce the parasitic loads between the engine and the wheels.  Every belt driven accessory gets it's power from the gas in the tank, so reducing the accessories will noticeably improve mileage.

-I replaced the stock engine driven hydraulic clutch cooling fan with an electric one.
The fan adds to the battery load, but it is much lighter, so it does not require as much force to turn. Also, it is only needed when driving very slow or idling, as otherwise the movement of the vehicle provides air flow. The stock fan turned at all times, no matter what temperature the engine was at.
This also helps the engine run warmer, which makes it more efficient in cold weather.

-I replaced the belt driven mechanical vacuum pump with an electric one.
This step is only relevant to diesel engines, as gas engines generate vacuum directly (no need for a pump) - unless you coast with the engine off. With an electric vacuum pump the brakes work the same whether the engine is on or off.

-I removed the power steering pump and replaced the steering gear with one meant for manual steering. Even in a truck this size, the only time it is at all difficult is when turning the wheels at a complete standstill. Other than parking in tight quarters, power steering is totally pointless.

All electric power in a car is generated by the alternator, which is powered by the engine, so any reduction in electric draw ultimately reduces drain on the engine.

NOTE: If anyone is inspired to do a similar project (with any vehicle), do not just disconnect the alternator from the battery w/o disconnecting the smaller wires. It will continue to produce current, but since that charge has nowhere to go, the alternator will self-destruct.
Also, diesel trucks tend to have very large batteries. Mine has two. This gives me a lot of reserve power to tap into without draining them too much. With an ordinary car battery you will damage it by cycling it too deeply. Once it finally dies, replace it with a deep-cycle (RV or marine) type battery and you'll be fine.

-The orange (on an '83 F-250) wire running from the external voltage regulator to the alternator controls whether the alternator is charging or idle. If you open the circuit the alternator stops charging. Even though it is still being turned, there is no resistance, it just freewheels. At first I just disconnected the wire, and later I installed a switch so that if the battery ever does run too low, I could charge it with the engine just by flipping the switch.
I used it so little that I eventually just removed the alternator altogether, thereby eliminating the belt and a little bit extra weight.

Since the battery is no longer being charged by the engine, I needed to reduce the electric load as much as possible so the battery will last.
I installed a 15watt solar panel to charge the battery. It sits on the passenger side of the dash board while driving, but when I stop I place it on the roof to get more direct sunlight.  If I drive for several hours (with my 400W stereo system on), the solar panel can fully recharge the batteries in about 2-3 days of full sun.  If I need to drive again sooner than that, I also have an onboard 120v AC charger which plugs into a standard wall outlet, much like a plug-in hybrid.

-I ordered extra bright LED bulbs (from for the taillights and tun signals. They are brighter than stock but draw less power. The original parking/brake/signal lights together use more power than the headlights, at 63 watts (parking) to 177 watts (brake) stock. The LEDs total 5.5 to 20 watts.

-The dash lights alone used 15 watts. When I took apart the dash and instrument gauge, I discovered that the original system deliberately blocked and wasted the majority of light the bulbs put out by covering them with a slightly translucent cover, and then shielding the gauges on 3 sides. Which explained why the dash was always so dim. I broke off the filters, cut away the plastic shielding, and instead built reflectors (out of metal tape) to direct the tiny amount of light of my new bulbs on to the gauges. The result is far brighter than it was, and is all red which is easier on night vision, and uses less than 1 watt for all 8 bulbs together (plus it looks really cool).

-I added a voltmeter so I can monitor the batteries.

-I had been thinking about making a buzzer to remind me if I left the lights on, but then it occurred to me that there is really no situation where I need the lights on and don't have the keys, so while I had the dash apart I also rewired the headlights (and aux driving lights which I also just installed) so that they go off when the key is turned off - now I can't possibly accidentally leave them on and drain the battery.

-If I had air conditioning, I would have removed it.  But I didn't to begin with.  You can stay cooler with beaded seat covers over thin white fabric and heat-blocking lightly-tinted window film, available from any auto parts or hardware store for around $15.  Last summer I painted my roof silver to reflect the sun light and keep it out of the cab.  I also have a small 12volt fan on the dashboard.
If you absolutely can't stand the heat, even with the roof painted silver, heat blocking window tint, beaded seat covers, and a smll fan blowing, you can always roll down the windows just a crack to provide additional ventilation.  Opening them just slightly still hurts your aerodynamics less than rolling them down all the way.
It also helps to wear no more clothing than is legally necessary.

Step 4: Facilitate Coasting

Driving with the engine off provides a couple challenges:

The ignition switch isn't designed for such constant use, but more importantly the power steering and power brakes go out.
(Note: Laws vary from state to state. In CA it is illegal to coast downhill in neutral. It is not illegal to coast with the transmission in gear, but the clutch held in.)

-I installed an electric vacuum pump to run the power brake booster.
These were standard on a number of late 80s American full-size cars, so I was able to pull one from the local wrecking yard. This change removes a drain from the engine (diesels have a belt driven booster pump) and prevents the power brakes from going out whenever I shut the engine. Stopping a 2 1/2 ton truck with just the power of your calf muscle is doable, but can be somewhat challenging.

-I switched to manual steering. This both removes the parasitic drain of the power steering pump from the engine, and means that the steering is not affected by shutting off the engine.

-I wired in a kill switch and remote starter onto the gear shift lever which means I don't need to use the key at all.

The switches I got from the local electronics place are dual purpose: wire them one way and they are momentary open, wire them the other and they are momentary closed. I used one each way, so that one stops fuel to the engine, the other triggers the starter. I mounted them side-by-side in a block of scrap wood, attached to the gear shift with a strip cut out of a steel can lid.
As I had hoped, they definitely make coasting downhill and killing it at red lights much faster, simpler, more precise, and safer, then using the key each time (especially since the ignition on this truck has been very finicky as long as I have had it) which encourages me to do it a lot more often.

If you happen to own a 7th generation (80s) Diesel F-250, and you want to wire in a kill switch or remote starter:
The thick red wire with a green stripe goes to the injector pump (for a kill). Wire the switch normally closed in series with the red wire. Since I didn't have any wire as thick as the one I was tapping into, I used two thinner wires in parallel.
The thin red wire with a blue stripe goes to the ignition relay (for a start). Wire it in parallel to a normally open switch. The other end of the switch goes to 12v positive. Ideally find an accessory (no key off) circuit. Some accessory circuits drop voltage slightly due to their load and therefor aren't strong enough to trigger the relay. I ended up wiring to a constant hot lead, which means the starter can be turned over even with out the key in (not a big deal, because it won't catch)

Step 5: Major Changes

-Once my tires wore out, I replaced them with low rolling resistance tires.  There aren't many LRR too chose from for large trucks.  With installation they cost $800.  They may well not pay back in terms of fuel used.

-When I can afford it, I will eventually replace the 3 speed (plus extra low) transmission with a 4 spd (plus low). I swapped out my BorgWarner T-18 for a ZF-5.  As expected, having an overdrive gear dramatically increased my highway mileage, from my previous best of 30 all the way up to 38. 

-Some people have made large extensions off the rear of their cars called "boat tails" which cause the rear to taper in at an aerodynamic angle.  There is a guy who gets 90mpg in his Honda Civic.
This would be impractical for me, because of how I use the truck, I am currently experimenting with a way to boattail the truck that doesn't affect its operation or capacity.  I have not yet determined if it helps.


-When I can afford it, I might lower the truck about 6 inches.  This will make it more aerodynamic, improve handling, and make it easier to load things onto the tailgate.  Sometimes I do need the extra weight capacity (or ground clearance) so I'll add in air suspension so I can raise it when I need to.

-I won't go through the trouble, but installing a turbo charger increases mileage (assuming you don't waste the extra power on accelerating faster)

-I have heard of people replacing the entire steel truck bed with aluminum to save weight. I am not going to go to that extent either.

-below are some random pictures of what this truck does.  They have nothing to do with this step.

Step 6: Additional Steps

Most of these steps don't apply to my vehicle, but I thought I would pass on some general tips.

-remove all excess weight; things like junk in the trunk, spare tire ('spare in a can' does actually work - or just carry a cell phone), for the truly dedicated, the entire rear seat.

-don't use the AC. Better yet, take it out entirely.

-keep the windows up at highway speeds. Yes, with no AC it will be hot. Use the cars vents, take off your jacket, and deal with being slightly uncomfortable. It helps to have a beaded seat cover, and a small fan that plugs into the cigarette lighter.

-use a ScanGuage or MPGuino. It wires into the car's computer to give you instant mileage and other data.

-the basic recommendations: keep the engine tuned, tires inflated (to the sidewall maximum, or possibly even slightly higher), combine trips so the engine stays warm.  Use a block heater if you have one.

-For more tips, and driving style and mileage mods in general, try: