My first encounter with how a diesel engine works was in Mexico, 1981. Diesel fuel was quite a bit cheaper than gasoline and a lot of folks in "the Valley" had diesels that they re-fueled across the border. I was living in Monterrey and the head of the orphanage had a green diesel pickup. I knew very little about diesels at that time other than the fact that you had to wait for the glow plugs to warm up before you tried to start it.

Twenty-two years later and diesel cars and trucks are everywhere now. There are over 1 million diesel powered trucks on the road today, in addition to thousands of diesel powered automobiles, farm tractors, buses, construction equipment, marine engines, and stationary engines. Every one of them needs lubrication. Today more than 215 million gallons of diesel engine oil is sold annually, not including the 13.8 million gallons of factory fill.

Why do people buy diesels? Are diesels better? Why do many people switch back to gasoline engines? And finally, what does any of this have to do with changing oil?

WHAT'S THE DIFFERENCE?
Both gasoline and diesel engines use a piston in an enclosed cylinder to develop power. As the piston rises in the cylinder, it compresses the space about it, generating heat. A mixture of fuel and air in this compressed space is ignited, causing it to burn and release gases. The gases expand, forcing the piston down. This turns a crankshaft and generates power.

The difference between a gas and diesel engine is that in a gasoline engine, fuel and air are pre-mixed before being released into the cylinder. A spark plug ignites this fuel-air mixture and away we go.

In a diesel engine, air alone is compressed, raising its temperature. Fuel is then injected into the heated air, causing ignition.

Between diesel engines, there's also a difference in how fuel and compressed, heated air are mixed before combustion. In most heavy-duty diesels, air is compressed and fuel is injected right in the cylinder. In most light-duty diesels, a small amount of heated air is trapped in a pre-combustion chamber first. The fuel is injected there, causing part of it to ignite. The ignition then continues into the cylinder, where the rest of the fuel mixes with the heated air and burns.

The advantages of a pre-combustion chamber are quieter operation, more efficient combustion of the fuel and lower exhaust emissions. In some applications, pre-combustion chambers are used in heavy-duty diesel engines as well.

WHY DIESELS ARE POPULAR
Diesels have been popular for a variety of reasons. There was a time when diesel fuel was significantly cheaper than gasoline and maybe some diesel owners hope it will be that way again some day.

The primary reason people like diesel engines is due to the way the engine delivers power. Gasoline engines deliver their power at higher RPMs. Anyone who ever burned rubber in a muscle car knows that you rev it up before you pop the clutch. Diesels deliver their power almost at idle. As a result diesels operate at lower engine rpm and higher torque. Higher gear ratios can thus be used, thereby improving power, efficiency, and fuel economy. Because diesels generate peak power at lower rpm (2000-2100 for diesel vs. 4000 rpm for gas engines), they have a much longer service life.

The benefits of diesel engines have made them the most common "workhorse" in trucking, shipping, construction, farming and industry. Their adaptability to automobiles and small trucks has proven to be successful and today more and more light-duty vehicles are being equipped with diesel engines.

DIESEL DRAWBACKS
Unfortunately, diesel engines are plagued by a host of disadvantages as well, some of which can be used to advantage by an astute quick lube operator.

First, diesels are notoriously sensitive to dirt and water contamination. Impurities in diesel fuel can seriously affect the efficiency of combustion. As a result, exhaust emissions, especially smoke, are greater.

Cold temperatures are also a problem for diesels. Diesel fuel will thicken or gel to the point that it will not flow through the fuel system. Reduced cranking speed at cold temperatures may produce insufficient heat during compression to ignite the air fuel mixture. The engine is cold, fuel is cold, air is cold, and your hands and feet are cold as you try to figure out what to do next.

Although diesels are built sturdier, when they do require maintenance they cost more to repair. Replacement parts are more expensive, maintenance costs higher, and qualified mechanics often hard to find. This ties in with the broader frustrations associated with the most basic services. Many places don't carry diesel fuel. And many shops say, "No, we don't work on diesels."

Finally, there's the smell. Possibly the number one reason people get rid of their diesels is that they get sick of everything they own having a whiff of diesel on it.

LUBE OPERATOR'S PERSPECTIVE
One thing you can do is recognize that diesels represent a growing opportunity. Diesels have larger sump capacities and require larger filters. You can make more profit from some diesel filters than on your oil changes. To attract these profitable diesel customers put out a sign that says, "We Service Diesels." These people are already frustrated finding basic services. Lure them in.

In addition to the usual need for filters and wipers, diesel cars and trucks often require fuel additives for improving operation. Become familiar with the various products on the market that address the diesel problems cited above. There are a number of products out there that clean the fuel system, improve combustion, reduce emissions and black smoke, reduce gelling and help keep fuel stable in storage. To help raise the cetane numbers in diesel fuel several companies sell a cetane booster fuel additive. The key idea here is that there are products on the market that address the problems inherent in diesels. By becoming familiar with these issues you can meet a customer need and profit from it.

Synthetic oils are another way to improve diesel performance. We've noted that diesels tend to be dirtier. Synthetic diesel oils tend to be formulated with a stronger detergent dispersant additive package to help address the extra soot and by-products of combustion. Premium synthetic oils keep engines cleaner.

In addition, because of their higher film strength synthetic lubes are better at handling higher temperatures and loads.

For cold climate diesel owners synthetic oils are almost a must. We mentioned earlier the importance of starting speed. In frigid northern tier states conventional lubes cause engine drag that almost cripples the starting capabilities of a diesel. No one appreciates the lower pour points of a synthetic oil more than diesel owners.

Diesel pickup owners tend to be performance minded. Carrying added products such as cetane boosters, and premium synthetics will appeal to this consumer. These are the "muscle cars" of the new millennium.