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  • 1997 Dodge Ram 3500 Dualie Cummins - 30-MPG 1-Ton! - Diesel Tech

1997 Dodge Ram 3500 Dualie Cummins - 30-MPG 1-Ton! - Diesel Tech

No-Buck Fuel-Saving Tips And Tricks

Jason Sands
Jul 27, 2007
Photographers: Jason Sands
Photo 2/13   |   1997 Dodge Ram 3500 Dualie Cummins front View
Go ahead and don't believe the numbers. The whole point of this article is to show how little tips and tricks can get you unbelievable fuel-economy figures-and it worked. If we hadn't been there filling the tank ourselves, we would've had a hard time believing the 30.94-mpg figure our cell phone calculator spit out after we filled the tank. There it was, though, we almost reached 31 mpg in a 1-ton dualie diesel all for the price of $9.26 in modifications.
It all started when we talked about different ways to increase our '97 Dodge Ram's fuel economy. Getting 21 highway mpg in stock form (3.54 axle gears and an automatic) wasn't bad, but there was more to be had. Reducing rolling resistance, improving engine efficiency and the truck's aerodynamics, and becoming more aware of your driving habits are all a big part of increasing fuel economy.
Rolling Resistance
This one was pretty easy. The point was to use low- or no-buck modifications, and only so much could be done to reduce the friction between the tires and the road. The recommended tire pressures for our vehicle were 65-psi front and 60-psi rear. Our actual pressures when measured turned out to be about 55-60 psi all around, so we had our tires inflated to 70-psi front and 65-psi rear to get a little less rolling resistance and a little more mpg.
Engine Efficiency
This one was a little hard without any type of tuning available because our 12-valve Cummins is mechanical, and we couldn't put in an economy tune anywhere. We heard diesels liked running a little hot, so the electric fans on the truck were turned off until engine temps reached 210 degrees F. Other than that, no changes were made to the engine.
This is where things got fun. Ultrahigh mpg hybrids have incredible aerodynamics. The Toyota Prius, for instance, has a drag coefficent of 0.26 compared with a Z06 Corvette's 0.36 (a truck comes in at 0.40-0.45), so aerodynamics play a large role in mpg. They don't call it 200-mph tape for no reason, so with a $9.26 roll of clear duct tape, we were in business. We taped off everything we could, made special aero hubcaps out of cardboard, and even blocked the grille off for aerodynamic purposes-even though many people we talked to were sure the engine would overheat. We drove with the windows up and the mirrors folded in to get every last bit of aero we could out of our truck.
Driving Habits
Changing driving habits proved to be a big factor. We slowed down to 60 mph wherever we went, coasted down hills whenever possible, and put a block under the gas pedal to limit us to half throttle while climbing hills. Under full throttle, our gas mileage would sink to about 10 mpg, so we had a throttle block to keep us from flooring it when we got antsy.
The Results
How did it all come together? Imagine driving a truck that's running hot with the windows up at 60 mph across the desert, the mirrors folded in so you can't see, and no A/C because it creates more engine drag. It was hot and miserable inside the cab, and at 60 mph, we didn't pass a single car.
Breathing through just the foglight holes, the truck never even got close to overheating. The engine temperature stabilized at 205 degrees without the fans even coming on. The result of all these shenanigans was a ridiculous 31 mpg.
In follow-up testing (to see if the figure was a fluke), the truck still averaged 26 mpg at speeds ranging from 70-80 mph with just the tires aired up and the grille blocked off, making our 31-mpg number seem believable. We also measured this as purely highway mpg, from freeway-exit gas station to freeway-exit gas station to make sure we had a fair comparison between modifications-no city traffic at all.
The funny part is we think we could still get more out of it. We didn't seal the bed off with any kind of cover, we didn't take the rear dualies off for less weight and less rolling resistance, and we didn't lower the truck. Although this article was done mostly for fun, there is no reason a properly lowered rig with low-rolling-resistance tires and a gear change shouldn't get 25 mpg on the highway.


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