As diesel fuel hovers between $4.50 and $4.95 a gallon, knowing how to improve diesel fuel economy is likely right at the top of your list, weather you drive a new Diesel Jetta TDI or a Chevy 2500 with a Duramax. If you are averaging over 40mpg in your new Jetta TDI, you may not have the same yearning for that knowledge as if you just finished pumping about $150 worth of Chevron’s finest into the saddle tanks of your 3/4 ton tow rig, but you get the point nonetheless.

With that in mind, here are some tricks you can use to get better fuel economy out of your diesel, weather you use it for towing, long freeway cruises, or just drive to work everyday like the rest of us poor slobs.

Diesel engines are internal combustion engines like gasoline engines but there are some important differences, the main one being they have no spark ignition system and burn a more oil-like fuel. The lack of an ignition system minimizes maintenance, such as the requirement to change spark plugs, spark plug wires, distributor cap and rotor, because there aren’t any! Most modern cars have eliminated all these parts except for the plugs themselves anyway by going to a coil-on-plug ignition system. If you’ve ever had to replace your coils on one of the new cars, you’ll probably long for the good old days of a traditional distributor that you could pick up at any auto parts store for $20.

Diesel engines use direct fuel injection systems. These inject the fuel directly (Hey, imagine that!) into the combustion chamber where it’s ignited by the heat produced by the diesel engine’s extremely high compression ratio. Some new gasoline engines, such as the new Cadillac 3.6 liter V-6, 2009 Porsche flat 6 engines, and the newer Audi engines are also using the direct fuel injection technique, combined with the gasoline engine’s spark ignition systems, to gain efficiency and maximize fuel economy.

So if you are driving an oil burner, how can you stretch every last mile out of a thankful?

For diesel powered vehicles many of the same fuel saving techniques apply as are used for gas powered vehicles; drive slower, clean out excess weight, don’t have a loaded roof rack if you don’t need to, keeping tires properly inflated, etc. There are some diesel specific fuel economy tricks, however that can be used to really make your gas powered brethren a bit jealous as you bypass the gas station.

How to Maximize Diesel Fuel Economy –

Learning how to correctly drive a diesel engine for the best fuel economy is very important, especially if you’ve spent your life behind the wheel of gas powered vehicles. Diesels just work a bit differently, and have about half the rpm range of a comparably sized gas engine. You’ll usually be turning much lower rpms on the freeway when driving a diesel powered vehicle, and that’s just the way these engines like it.

Use the cruise control –
One of the reasons that diesel engines are often chosen for duty in heavy commercial applications such as generators and pumps is that they like to be operated at a constant speed, and are most efficient when run that way. Remember that in your daily driving. Find the rpm that your engine is the most efficient for a given load and stay there. Use your trip computer to find the best instant mpg speed at the load ranges that you normally use and chart them. When traveling on the freeway set your cruise control for these speeds.

Short shift the engine –
Short shifting is a driving technique for manual transmission vehicles where the engine is shifted into the next gear well before its power peak and red line. For drivers that are accustomed to driving gas powered vehicles this may seem counter intuitive, but diesels typically don’t like to spend their time in the upper reaches of the tachometer. Shift at maximum torque point, which on diesel engines tend to be fairly low in the RPM range.

Choose a lower final drive –
If you’re buying a new pickup or SUV with a diesel engine option, you’ll often have a choice of different rear end (final drive) gear ratios when perusing the option sheet. Unless you’ll be spending most of your time towing very heavy loads (6,000+ lbs.), choose the lowest numerical ratio that’s available. If you’re searching for the best fuel economy, the lower (numerical) gear will really help you get it.

Don’t buy bargain basement diesel fuel –
Diesels are very sensitive to the quality of their fuel. One of the worst things you can do is feed them contaminated fuel, especially if it contains water. Steer clear of the low budget stations. The few cents a gallon you save could come back to bite you.

General Motors actually issued a technical service bulletin (TSB) relating to fuel economy in its diesel powered trucks. This would apply to most other brands of diesel trucks, in addition to SUVs and cars. Here are the factors listed in the GM TSB that can affect diesel powered fuel economy:
• Accessories that increase wind drag. Keep the bike rack, or ski carrier off your rig when you’re not heading out to the mountain. This is especially harmful to the mileage you’ll get in a diesel car with a smaller engine, as it causes it to work much harder than the same wind resistance increase on a big-engined diesel powered rig like a Duramax or Cummins pickup.
• Driving 65mph will lower fuel mileage up to 15% as compared to driving 55. This is especially true when towing a heavy load that has poor aerodynamics and a large frontal area, like your big wakeboarding boat with a tower.
• Frequent stops, changing speeds or otherwise poor driving habits. Diesels love steady state operating conditions and prove it by returning their best fuel economy when operated that way. Find the best fuel economy speed for a given load and just set the cruise control for that speed.
• Transmission problems such as OD automatics not shifting into OD, or the lockup torque convertor not locking up.
• Fuel system problems such as contaminated fuel filters. The fuel filter on a diesel is even more important than on a gasoline engined vehicle. Make sure the water separator is functioning properly.
• Final gear ratio. As noted above, when purchasing a new truck check the option box for the lowest numerical ratio possible unless you’ll be spending a significant portion of your time towing heavy loads, in which case you’ll want to go to a lower (higher numerical) gear ratio in the rear end.
• GVW (Gross Vehicle Weight).
• Wheel alignment and tire pressure – check your alignment and tire pressure. If either of these are out of adjustment or spec, it increases rolling resistance and reduces fuel economy.
• Misadjusted or dragging brakes – the same as above. In addition, make sure you don’t ride the brakes when driving. This behavior is fairly common, as evidenced by the dodos cruising down the freeway with their brake lights on.

Using diesel fuel additives –
Diesel engines burn a very different fuel than gas engines. One of the most important ratings that describes diesel is its’ cetane rating. Cetane is a measurement of its propensity to burn and support combustion; to a point, the higher the better.

Most commercially available diesel fuel runs around a 40 cetane rating. Not bad, except that most diesel engines found in pickups, such as the Duramax, Cummins, or Powerstroke like about 5 – 10 points higher than that. One way to raise the cetane rating of what you put in your tank is through the use of fuel additives. Diesel additives will also increase the lubricity of the fuel to help protect engine components and decrease internal friction. Both of these effects will increase your diesel’s fuel economy.

Take a look at the post I did last on the 3 best car modifications to increase gas mileage. The same 3 mods apply for diesel vehicles, and for many of the same reasons. In fact, one of them, reprogramming your diesel’s ECU, is one of the favored mods to radically increase your diesel’s power and torque too. The sophistication of the new controllers is pretty phenomenal. They can allow you to select different settings depending on your current use. If you’re towing for example, you can just dial up more grunt, but keep more conservative programming for daily driving to save fuel. They can even tell if your transmission is slipping and reduce the fuel to save your tranny.

This is a beginning primer on how to maximize fuel economy for your diesel powered car or truck. Since better fuel economy is one of the main reasons people buy diesel vehicles, there is a bit of gold in here.

Until next time.

Please Stumble My Post!