The Definitive Guide to Understanding Diesel Engines Versus Gasoline Engines

definitive guide diesel engines gas engines

In many ways, understanding how diesel engines versus gasoline engines work is a simple thing. When you peer into the matter carefully, there are profound differences. We will look at both engine types from a variety of angles and provide you with a good overview of all aspects. Where should we begin? Why with the fuel itself, of course!

To better understand why there are two similar but disparate engine designs using two very different fuels, we need to look at history.

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The evolution of engines came about just as the fuel they utilized evolved. In the 1800s, steam engines were already quite popular, but, as the industrial revolution took place and magnates like John D. Rockefeller began exploiting oil, the internal combustion engine came into being. Both gasoline and diesel engines are, indeed, internal combustion engines, albeit with different compression ratios. The number two diesel fuel used today in cars, trucks, and farm equipment is much like a refined oil, but gasoline is lighter and enjoys a greater refinement.

Rudolf Diesel is credited with the invention of the engine that bears his name today, and he opened his factory in Paris, France in 1885 to develop this modern marvel. It took him over ten years and many patent filings to make it happen. He sold portions of his invention, along the way, to the Swiss-based Sulzer Brothers.

Meanwhile, other famous names like Gottlieb Daimler and Karl Benz were busy creating various gasoline-style engines following the progenitor device invented by George Brayton in the U.S. Thus, both gasoline and diesel style internal combustion engines got their start over a similar historical period and have been in a kind of competition ever since.

internal combustion engines graphic

Internal combustion engines necessarily operate within specific parameters governed by the laws of physics. The Carnot cycle, which outlines the efficiency of an engine with respect to its temperature and pressure, indicates that the best operating temperature for modern engines hovers at 183 degrees Fahrenheit, just below the boiling point of water at S.T.P. (Standard Temperature and Pressure), but far too hot for human touch.

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Today’s engines are almost universally four-stroke design. The stroke describes the various things that happen as the mechanism moves. Both diesel and gasoline engines have these four strokes. They both have pistons and chambers where explosive firing causes a crankshaft below to turn with force.

This works the same in both engine types, including the Ford diesel Powerstroke parts which have improved the engine design. It is also generally true that you will find lots of stores selling gasoline engine parts and much fewer selling diesel truck parts.


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Any kid growing up can stand next to a car or truck idling at the gas station and hear the difference between the sound of a diesel versus a gasoline engine. While the gas engine is a rather smooth, throaty piece, the diesel has a certain clicking and purring that some find infectious.

These differences in sounds are due to how the fuel is mixed in the two respective engine designs. The power that the two disparate fossil fuels possess to explode and create the force that drives the engine is different. The explosive mixtures have a different flash point, and the explosion takes place at a different pressure within the cylinder.

The diesel requires more pressure than the gasoline, hence the higher compression ratio. Designing the respective engines with their own perfectly timed firing and keeping them running like a fine-tuned watch is the whole idea. From the standpoint of horsepower, the two systems compete very well with each other.

black dodge ram parked in lot


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Thinking of mixing the two fuels? Not a good idea at all! There are stories about farmers who have used all kinds of odd fuels to run diesel engines, and the truth is that a diesel engine can be a wee bit more forgiving. Refined diesel is an oily fuel, and, indeed, the engines can be tuned to accommodate so-called biofuels—engines adjusted to run on used fryer oil or corn oil.

In practice, this is not an effective way to operate your engine. It runs best on refined number two diesel fuel.

Can mistakes happen? Definitely! There are plenty of stories about folks who have accidentally put gasoline into a diesel vehicle and vice-versa. If that should ever happen to you, the best thing to do is turn off the engine. Diesel and gasoline engines are timed differently because of the flashpoints of the fuel. The two fuels are incompatible with each other’s engines.

Additionally, the oily component of the diesel fuel serves as lubrication to the injectors—something gasoline doesn’t provide. The weight of the two fuels is different. Diesel sinks to the bottom, and gasoline rises to the top of the tank.

Should a situation occur where the fuel in your vehicle has been compromised, don’t risk operating the engine and suddenly be hunting for new diesel injector parts. Avoid an adverse outcome and potentially ruining your engine. Shut it off, then drain the tank.


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Diesel engines are designed with fuel injectors, while early gasoline engines used carburetors. The science behind engine design has now evolved in ways that include fuel injection on some gasoline engines as well.

Traditionally, gasoline engines would create just the right mixture of vaporized gasoline and air before entering the combustion chamber. A spark would cause the explosive mixture to ignite and force the piston back down away to its first position and, in doing so, apply the force to turn the crankshaft of the engine powerfully. The mixture was transferred by way of a vacuum, which was amplified using the Venturi effect that uses variations in the diameter of the tube to alter to force of the material passing through it.

Diesel engines start the process in a different manner, sending air into the combustion chamber and injecting the fuel just as the pressure of the air becomes sufficiently hot to ignite the fuel and create the explosive force.

So, while fuel injection design is optional on the gasoline engine, it is an inherent aspect of the diesel engine. So, too, the availability of diesel fuel injector parts can be problematic, and finding a good supplier is essential.


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turbocharger car parts

A supercharger or turbocharger is a fabulous thing. You can use them on both diesel and gasoline engines. The idea is that the more air you can force into the combustion chamber, the greater the degree of the explosion you can create, given that the fuel needs air to burn. Turbochargers add horsepower and potential torque to engines. They can turn an average gasoline engine into an extremely peppy power plant and, in the case of diesel, they can really make your vehicle get up and go!

In diesel configurations, it is not unusual to place turbochargers back-to-back to create an even denser column of air for insertion into the combustion chambers. Properly tuning the components to account for the denser air is required in both gasoline and diesel configurations where turbochargers are employed. This applies to standard engines, including diesel Powerstroke parts in the Ford design.


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Fuel additives can be very tricky things. At the very basic end, your engine is designed to work with a particular fuel, whether that is gasoline or diesel. In the case of most diesels, this will be number two diesel fuel. In the case of gasoline, it could be one of the several types of octane fuel.

Muscle cars of the 1960s and beyond were famous for “liking” higher octane fuels to achieve their full performance. Because the technology has advanced so thoroughly today, where computers control the mixture of fuel and air, “monkeying” around with additives that might boost octane is risky.

Remember, in either engine design, the idea is to have the cylinders fire at exact times in the cycle. When altering the octane in the gasoline, this just adds to the power of the explosion, but, in the case of diesel, it can create pre-ignition, which reduces the horsepower rather than adding to it.

Today’s modern fuels often add ethanol to the gasoline to “stretch” out the gas supply. Technically, ethanol adds octane value to the fuel. It does burn. The potential ill effects of ethanol, if any, come because of its molecular structure. There are characteristics of the ethanol molecule that impart special power in its ability to dissolve things as a solvent. Some mechanics would like to think this can include engine parts, like seals. You will see a handful of gas stations who tout selling “ethanol free” gasoline.

You may fear that using the wrong fuel additive might have you later hunting for diesel truck parts—and you could be right. Manufacturers post specifications for the fuel they recommend for any given engine. In general, you should adhere to them. If you attempt to use additives in either your gasoline or diesel fuels, you should be advised the engine will likely need to be re-timed to work its best, and that timing can be affected by the characteristics of the fuel.

adding fuel to car pump


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The exhaust system of a car or truck is a critical component of its operation. Getting the exhaust gases out of the combustion chamber is part of the design. The size of the pipes affects the back pressure on the engine. Having nearly no exhaust pipes or muffler, like you might find in a vehicle for off-road racing, pretty much eliminates the back pressure. When you tune your engine to operate in that way, you can achieve an additional boost in horsepower.

In the real world, we use mufflers and have pipes that transfer the exhaust to the tail end of the car. Thus, a more realistic scenario is one where the exhaust is modified with larger diameter parts that reduce the back pressure on the engine and better facilitate the flow of the exhaust gases. Finding the diesel truck parts you need before you attempt to modify any system can be daunting, and having a reliable supplier is essential.

Remember, any change in the manufacturer’s original design will also necessitate an adjustment in the tuning of the engine to accommodate the system.


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While many would never think of stressing their vehicles whatsoever, there are some who like doing so. You can see them lining up their cars and trucks at the drag strip on weekends all over the country. While you might not think of a diesel truck as a racer, you might be surprised at how fast a four-wheel drive will launch out of the box at the track. While the transmission governs much of the speed factor in any vehicle, both diesel and gasoline engines can be formidable.

gasoline diesel engine speed quote


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Over the course of the last few years, both gasoline and diesel prices have greatly fluctuated. During most of the twentieth century, diesel fuel cost less per gallon than gasoline. Turmoil around the globe makes for erratic price swings. Tuning vehicles to meet specific emission standards also wreaks havoc with mileage and, consequently, the overall cost of operating your vehicle. There is very little difference in gasoline versus diesel mileage because engine designs have become so good.  

Does a diesel engine last longer? In general, they do, but, in the case of many government fleets, these vehicles get replaced periodically anyway, and the longevity is not a factor in fleet management. There is a bonus for diesel, as it boasts a higher resale value.


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New cars or trucks frequently enjoy a certain period where the dealer maintains the vehicle. In such a scenario, gasoline versus diesel is not much of an issue. Diesel engines generally require a few days more maintenance per year than gasoline engines. Getting the most out of a diesel engine requires some add-ons you may not have in your gasoline powered vehicle, like a supercharger or two!

Optimizing the operation of a diesel engine can also include modifications to the transmission and exhaust. These additional things which add complexity to the machinery can be problematic.

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If you become the owner of a diesel-powered car, you might realize that there are fewer qualified mechanics available than gasoline-powered cars. Both gasoline and diesel engines do have prescribed maintenance schedules that are recommended by mileage on the vehicle.

Depending on how you use the vehicle, how often it idles, and whether the mileage is from city or open road driving, your maintenance schedule will vary.

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