There was a time when diesel power was considered something only a trucker could love. A diesel engine was fine for long haul trucks, but the ones Detroit made available were underpowered and fraught with trouble. Even today there are plenty of folks who have never forgiven certain manufacturers for their idea of a diesel engine — and may never.
But times change and the diesel engine has, as well. Chances are, most landscape professionals now use or own a truck equipped with a diesel engine and, in fact, wouldn't be without it. Likewise, Mercedes has introduced a new, more powerful diesel engine, and Volkswagen is selling them in Jettas and Beetles.
The difference between the diesels of today and those of the past lies in the details. With computer-controlled timing, more efficient injection systems and the addition of turbochargers, the diesel engine has made real inroads with the driving public.
So do these innovations spill over into grounds equipment? They do and this trend will continue. Now, more than ever, diesel is an option you should look into when considering your next equipment purchase.
RELIABILITY AND EFFICIENCY
There are differences, of course, between diesel and gas engines besides the type of fuel they burn, though we'll start with that. Diesel fuel actually contains more Btu (British thermal units) of power per gallon than does gasoline, and partially as a result of that, the diesel engine is more efficient. Differences in fuel economy can really add up — anywhere from a 12- to 30-percent difference, depending on application and engine displacement. Another important factor is that diesel fuel is much more stable (less explosive) than gasoline and, as a result, is safer to store and transport then gasoline. While it can and does go bad in storage, diesel's inherent stability makes it less likely to gum up than gasoline and more likely to survive storage. (However, a preservative is highly recommended for long periods of storage.)
Gasoline engines require an ignition source — a coil or electronic ignition of some sort to initiate combustion — and a spark plug to arc and ignite the fuel on the compression stroke. These are items that require routine maintenance and eventual replacement. Diesel engines rely upon a sophisticated fuel-injection system that sprays the right amount of fuel at the right time for the most efficient burn rate. The main area of improvement in truck diesel engines has been in this area, and small diesels are no exception. However, the sophisticated technology also serves as a disadvantage as well — should you ever have trouble, you'll need to pay a professional to fix it.
HOT AND COLD
Diesels rely on compression — very high compression to ignite the fuel. There are no spark plugs or related components on a diesel engine. Compression ratios range from 17:1 to 22:1 in diesels, versus 6.5:1 to 9.5:1 in gasoline engines. To alleviate cold starting problems, many are equipped with glow plugs (which preheat the combustion chamber) or intake heaters that heat the intake path to the engine. These two advances have made them more cold-weather friendly, but gasoline engines still hold the edge in cold weather starting. Due to the high pressures inherent in diesel engines, they are very robustly built, with thicker cylinder walls and stronger components than a gasoline engine.
With proper care, it is not unusual to get several thousand hours from a diesel engine before a rebuild is needed. Most air-cooled gasoline engines, by comparison, have an expected life of 2,000 hours or less between rebuilds. Liquid-cooled gasoline engines last longer than that, but still generally don't last as long as a diesel engine.
The big difference between a gas and diesel engine, of course, is power. While today's small diesels produce more power than ever before, gasoline engines are generally better for sudden acceleration and high horsepower applications, but diesel engines produce power at a lower rpm, and for a longer time. For example, a diesel engine may produce its maximum torque at 2,200 rpm and continue to produce it up to the governed speed of the engine.
A gasoline engine produces its torque at a higher rpm and, consequently, must run hotter in order to produce the same amount of power.
BANG FOR YOUR BUCK
Cost can be a factor in your engine decision as well. Gasoline engines are significantly cheaper than their diesel equivalents, so you need to consider your situation before deciding which type of engine to buy.
For example, if you operate a piece of equipment eight hours per day, 40 hours a week, 40 weeks a year, that is a total of 1,600 hours per year. If the gasoline engine consumes three gallons of fuel per hour and the diesel equivalent burns 2.5 gallons of fuel per hour, it results in a fuel savings of 800 gallons per year. Additional savings will be realized because you can purchase off-road diesel free of any tax, which costs from 20 to 40 cents less than diesel at the pump. That is enough reason to justify an $800 or even $1,000 difference in the price tag because you'll make it up rather quickly.
Of course, if you are buying a piece of equipment that sees considerably less usage, then gasoline power becomes more attractive. A diesel-powered walk-behind mower would be very durable, but also very heavy and very expensive. There are reasons, after all, why everything is not diesel powered.
Diesel engines require service, of course, and there are more filters to be concerned with on a diesel engine. There are the normal oil and air filters, then there is the fuel filter itself, which is more sophisticated than its counterpart on a gas engine. Also, some diesel engines have an additional fuel/water separator to keep moisture out of the fuel system, and this, too, requires service. Diesel engines are very intolerant of neglect, so they are not for those who don't maintain their equipment in a timely manner. However, properly maintained and operated, there are very few applications in grounds maintenance that they can't perform.
Diesel engines are, by and large, water-cooled and, as a result, have more moving parts and maintenance requirements than their gasoline counterparts. The advantage here is simple: Water-cooled engines — gas or diesel — run quieter and cooler than air-cooled engines; therefore, a water-cooled diesel should be a “two-for,” as it is both quieter than an air-cooled gasoline engine and more fuel efficient.
PUT IT TO THE TEST
Many major manufacturers offer the choice of diesel or gasoline power in their equipment. Before choosing, take a test drive with both types of machines, if possible — there really is no substitute for real world conditions. Secondly, investigate the availability of service in your area for both the gasoline and diesel versions of the machine. It is a fact of life that there are more gasoline engine repair shops than those that repair diesels, so make sure you can get service before spending your money.
Of course, you'll want to make sure there are plenty of places to buy diesel in your area, too — preferably, off-road diesel.
There are situations where gasoline makes more sense. As in the rest of life, all answers are not cut and dried. If you do all your own repairs and want to keep it that way, gasoline engines haven't changed much in the past 20 years. The main advances have been in overhead valves and carburetor jetting (in some cases fuel injection), and a gasoline engine on your commercial mower operates in much the same way as the engine in your car. For this reason alone, many folks will stick with gasoline as the power source for their equipment.
Contrast this with the diesel engine, which, if it requires injection pump or injector service, must be turned over to a diesel repair shop. The likelihood of such a visit becoming necessary go up exponentially with the amount of dirt or other contaminants found in fuel. Diesel engines will not tolerate dirt or other contaminants in the fuel, unlike a gasoline engine which is more forgiving or at least runs correctly after the carburetor has been cleaned. Dirt or water in a diesel engine is an expensive oversight, not so easily corrected.
Another area of consideration is trade-in value, if you make a practice of trading equipment. Diesel-powered equipment generally brings more money at trade-in time. This is due to the desirable elements covered above. Likewise, diesel-powered equipment generally brings more cash if sold outright.
PREFERENCE AND PARAMETERS
When considering equipment for commercial applications, the defining parameters are productivity, speed and durability. Diesel engines meet and exceed the parameter for profitability in most cases. You owe it to yourself to look into diesel power in your next purchase — they really aren't just for truckers anymore.
Paul Peterson is a repair technician for a large rental company. He has managed small engines shops, set up parts departments and worked in the outdoor power equipment rental business for the past 10 years (Bristol, Va.).
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