When I hear the term diesel, the first thing I always picture in my mind is an 18-wheeler. Then my thoughts drift to gleaming chrome stacks, tons of load-hauling torque and the sounds of a semi-truck. The next thing you know I’m kicking back to watch the greatest trucking movie of all time, “Convoy,” for what’s probably the 10th time.
I’m sure it’s generational, because growing up, diesel engines were only popular in heavy-duty trucks. Whether the big rigs defined the persona of a diesel engine or vise-versa I’m not sure, but to me the term “diesel” always has been synonymous with power and strength. So, what’s a light diesel? It seems like a contradiction of terms to me.
A light diesel in the simplest way of thinking is anything diesel-powered that resides in someone’s driveway as daily transportation, including everything from cars to pickup trucks. The true definition gets a little muddy at a certain point because the federal standards have different weight cut-offs for their light-truck classifications.
Using these standards, most full-size pickup trucks are all considered light-duty, even when they’re equipped with torque-monster diesel engines. But, if it’s a dually crew-cab 1-ton, it just might make it into the heavy-duty classification. Either way, it really doesn’t matter. Parts are parts, and if they’re driving it and fixing it, they’ll look to you – the counter professional – for what they need.
As with any subject, knowledge gives you the power to sell, so I’ll start with what’s different about a diesel. There are three things that diesels are typically known for: fuel economy; lots of power; and long life.
Why does a diesel engine get better fuel economy? Diesel fuel has a higher energy density than gasoline. This means that it takes less of it to produce the same amount of power resulting from combustion. Diesel engines also have much higher compression ratios than gasoline because the fuel is ignited by the heat of compression, and higher compression ratios in general lead to increased combustion efficiency.
Why do they produce more power? Although modern diesel engines have the ability to produce incredibly high horsepower numbers, the “power” normally associated with a diesel engine is actually high torque. Torque is low rpm power for pulling, and horsepower is the high rpm power for acceleration. Diesel trucks are designed for pulling, which is why torque is so important.
When the air/fuel mixture burns in a gasoline engine, it burns quickly, and the force of the expanding gasses drives the piston down in the cylinder. This creates power. However, once the air/fuel mixture has burned and the piston is traveling downward, the further down it goes, the less force is exerted upon it.
Diesel fuel burns slowly. When the combustion process begins, the force of the expanding gasses pushes the piston downwards, but the air/fuel mixture continues to burn as the piston travels downward, exerting continuous force on the piston until it nears the bottom of the stroke. This continuous force on the piston is why diesel engines produce so much torque. Modern electronic control of diesel-fuel systems has allowed them to precisely control fuel-injection time to maximize this effect.
Do they really last longer? As long as they’re properly maintained, yes – and here’s why. Gasoline is a harsh solvent with no lubricity. It wreaks havoc on everything it comes into contact with, including the inside of the cylinders in an engine. Diesel fuel, on the other hand, has a high level of lubricity, drastically reducing cylinder wear.
Another reason for increased longevity also has to do with the slower speed in which the diesel fuel burns. The combustion of gasoline is a violent process that applies incredible stresses on the rotating assembly, whereas the diesel-fuel combustion process is less violent, applying a steady, continuous downward force on the piston.
Then there’s temperature. Diesel fuel ignites at a lower temperature than gasoline, so combustion temperatures, as well as exhaust temperatures, are lower. And finally, there’s construction. Because of the higher compression ratios, diesel engines are built stronger and sturdier from the block and heads to the rotating assembly, often with increased oil capacity and improved oiling systems.
In recent years, there’s been turmoil and scandal related to diesel-powered vehicles, and now there’s plenty of speculation that the end of the diesel isn’t too far off. But diesel owners aren’t ready to give up – meaning parts opportunities abound. With fewer diesel vehicles available, there will be a stronger push to keep the current ones on the road.
Some areas of repair – such as timing belts, water pumps and hoses – ultimately don’t differ from a gasoline vehicle. However, an area where you can capitalize is maintenance. Diesel engines can last a long time, and that longer service life extends the opportunity to sell maintenance items.
An immediate area to take advantage of is fuel treatment. The fuel system is the heart of a diesel. Fuel quantity controls engine speed. There’s no ignition system, and there’s no air-volume control or throttle plates like those on a gasoline vehicle. (In case a customer decides to call you out, there are some diesels with throttle plates, but they don’t have anything to do with controlling engine speed – they only smooth out engine shutdown and increase exhaust-gas recirculation.)
Diesels have complex and expensive injection pumps and injectors. Not only does diesel fuel extend cylinder life with its lubricity, but it also preserves the life of the fuel system itself.
The problem is that in order to reduce air pollution, ultra-low-sulfur diesel fuel was introduced in 2006. By losing the sulfur, diesel fuel also lost the majority of its lubricity. This can be, will be and has been a big problem. Diesel-fuel treatments add back this lubricity, and while they may seem expensive to a customer, a small bottle treats many gallons, and if it’s properly measured, it ultimately only results in a minor fuel-cost increase.
Cold-weather performance is another problem. Diesel fuel has always had a tendency to gel in extremely cold temperatures, and the loss of sulfur has made it worse. Diesel-fuel additives will combat this problem as well. Additives also battle cylinder deposits, and on a diesel engine these deposits soak up diesel fuel and effect fuel economy. Fuel additives should be recommended for continuous use.
Next on the easy-sell list is filters. Air filters fall under standard replacement guidelines that you’re used to, but fuel filters are an area to concentrate on. Contaminants can be very damaging to diesel-fuel pumps and injectors, and water accumulation in diesel fuel is a common problem. Diesel fuel often is stored for longer periods of time than gasoline, and the water accumulation is a result of condensation from temperature change.
For this reason, almost every piece of heavy equipment has an individual water separator, and even many small diesel cars have water-drain valves in the bottom of their fuel filters. Generally, water accumulation isn’t a problem at larger-volume gas stations, but there’s no way of knowing for sure, so it’s better to err on the side of caution. Diesel-fuel filters should be replaced at least once a year.
Performance upgrades are common among diesel enthusiasts – especially intake and exhaust systems – but it can be a difficult market to get into since there are so many different options and applications. The best opportunities lie with accessories and upgrades that fit all models, such as gauges, lighting and interior accessories.
When diesel fuel burns, it leaves behind black soot. This soot finds its way past the piston rings into the crankcase and turns the engine oil black. Even when changing the oil, there’s almost always enough residual oil in the pan and throughout the engine that the new oil is black almost immediately. The soot doesn’t harm the properties and performance of the oil, but think of it like any dirt particles: If there’s too much of it, the oil performance will degrade.
It’s easy to see oil condition on the dipstick of a gasoline engine, but on a diesel there’s no way of telling. It’s critical for vehicle owners to document oil-change mileage so they don’t go over. It’s best to follow manufacturer recommendations for oil type, and it’s a good idea to recommend a high-quality oil filter. While diesel-powered cars typically have standard oil capacities, many pickup trucks have much higher capacities – sometimes 10 quarts or more. If your customer isn’t sure, take the extra step of looking it up so they don’t get home and end up short.
If your customer is doing an oil change, this is the perfect time to sell latex gloves, disposable rags and other cleaning supplies. Diesel oil will stain your hands for an entire day, and it doesn’t help the look of your garage floor either. We always should wear gloves to protect our skin during an oil change, but admittedly I don’t always do that on a gasoline vehicle. Diesel is a different story.
Diesel Exhaust Fluid
For the 2010 model year, the EPA mandated that diesel engines reduce the production of nitrogen oxides (NOx), which is linked to the formation of acid rain and smog. Diesel exhaust fluid (DEF) is what allowed manufacturers to meet these requirements. DEF is a solution of urea and deionized water that’s injected into the exhaust system before the catalytic converter. The chemical reaction forms ammonia, which then works in conjunction with the catalyst to convert NOx into nitrogen and water.
It’s ultimately a simple solution, but diesel owners need to keep the DEF reservoirs full. If the DEF runs out, the vehicle will not start. If they’re running, they won’t quit, but often go into a low-power mode.
Historically, diesel engines were known for difficult cold-weather starting, since the heat of compression ignites the fuel. Modern combustion-chamber design and technology have greatly improved this problem, but in the far northern regions of the United States and in Canada, diesel owners often don’t have a choice but to install a block heater. Even in areas where starting isn’t a problem, block heaters are popular in the winter since diesel engines take a long time to warm up.
There are two different types of heaters. Most factory-style heaters are designed to fit directly into the engine block in place of a casting plug, which places a heating element directly into the engine coolant. This is generally the preferred method, as it’s the most effective.
The second type of block heater is designed to mount flat on the bottom of an oil pan. The heat travels up through the pan and warms the engine oil. These are effective, but only given that they fit the pan properly and are out of harm’s way. Some factory applications are designed like this, but aftermarket designs are intended to be “universal,” and they don’t always work as well. Familiarize yourself with the heaters you have in stock, and what they fit, or where you can locate an application chart. Most people shopping for a block heater will know they want one – it’ll be an easy sale – but getting the correct one for the application is the hardest part.
Tips for Your Customers
The best advice you can give your customers is explaining the importance of diesel maintenance. A critical tip, however, involves replacement of a diesel-fuel filter. When a diesel runs out of fuel, air is drawn into the lines, and they simply won’t start until the air is bled out. Cranking the engine won’t do anything except overheat the starter.
Some diesel trucks and heavy equipment are equipped with primers, such as those you may be familiar with on small engines. They’re designed to draw fuel from the tank and fill the filter and pump. Some newer vehicles have electronic primers that do this when the key is cycled on, but many diesel-powered cars don’t have either of these features. When the fuel filter is replaced, it needs to be filled with diesel fuel before connecting the lines. It often requires a small funnel, and it can take a few minutes to get it done, but it’s mandatory.
Seasoned diesel owners should be familiar with fuel-filter replacement, but it never hurts to ask and make sure they are. You can save your customer a lot of trouble.