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What’s the Difference Between F-250 Diesel Engines and Gasoline Engines?

Fuel types aside, you may be asking why diesel and gas engines in F-250s are so different. We are all familiar with the difference in power produced by these engines, and we know one is better for daily commutes and the other for hard work. What makes these differences in performance characteristics are worth knowing in depth.2011-2016-f250-with-bed-cap-and-aftermarket-bumper.JPG

Table of Contents
  1. Compression Ignition vs Spark Ignition
  2. Four Stroke Engine Cycle Split
  3. Fuel Composition
  4. Power/Torque Curves
  5. Oil/Lubrication Differences
  6. Fuel Efficiency
  7. Air/Fuel Ratio Differences
  8. Weight Differences Between Engine Parts and the Engines
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The gasoline engines make their power in different spots along the RPM range. Gas engines have a higher redline, but diesels have superior torque. Building your respective F250 engine may be similar in some regards, but the fundamental combustion differences will dictate what upgrades you settle on.

F250 Engine Parts

Compression Ignition vs Spark Ignition

How the fuel is burned is the most defining differences between diesel and gas engines. Gas engines compress the fuel and air mixture together during the compression stroke. Once the piston reaches top-dead-center, a spark plug is triggered to initiate the burn. With a diesel engine, a much higher compression ratio is used, which increases the temperature of the air in the cylinder. The difference is the fuel is not introduced in diesel engines until the piston has compressed all of the air, which will combust the fuel as it’s introduced.

Four Stroke Engine Cycle Split

Although these engines burn fuel differently, they both operate on the 4-stroke cycle. The first stroke is the downward motion of the piston that draws air into the cylinder. The second stroke is the compression stroke, which is followed by the combustion stroke, and lastly the exhaust stroke. The only real difference in this cycle between diesel and gas engines is when the fuel is introduced and the compression ratios.

Fuel Composition

If you were to take diesel fuel and gasoline and compare them side-by-side, you could easily tell the difference between the two. Diesel fuel has a higher viscosity than gasoline, which means its closer to oil, while gasoline has a lower viscosity, which means it flows like water.

While gasoline engines are a little more forgiving in terms of what can flow through the fuel system, diesel is not. The fuel system of diesel trucks relies on the thicker diesel fuel to work as a lubricant for the fuel pump. Moving parts in the pump would wear down if the diesel fuel were lighter in viscosity, which can be harmful to the engine. This is why it’s so critical to make sure all contaminants, including water, are drawn from the fuel.

Power/Torque Curves

Most people are used to gasoline engines and their wide RPM range. Gasoline engines make power at high RPMs. In the 2019 F-250 with a 6.2 liter gas engine, the peak power, 385 horsepower, is achieved at 5750 RPM, and the peak torque, 430 ft/lbs., is made at 3800 RPM. These are impressive numbers but aren’t out of the ordinary for most folks.

Diesel engines have much lower redlines, but that’s no issue because they make power at way lower RPMs. The 2019 Ford F-250’s 6.7 Powerstroke diesel engine pumps out 450 horsepower at 2800 RPM and knocks the scale over with 935 ft. lbs. of torque at 1800 RPM.

Oil/Lubrication Differences

Engine technology has come a long way - diesel engines don’t need to run on heavier oil weights than gas engines. The oil does need to be formulated, which makes a difference in the type of oil required to run in a diesel engine than in a gas engine. These oils need to be formulated in order to handle the byproducts produced by either fuel type, and this is a major difference.

Fuel Efficiency

One thing you may hear is diesel engines get much better fuel economy than gas engines. While this may be true, with the F-250, good gas mileage is a term you may not hear often. The 6.2 liter V8 gas engine has been reported to get right around 15 miles per gallon average on the highway. Despite the diesel engine being much heavier and producing more power, this combination has been reported to get around 17 miles to the gallon on the highway. Neither is very high, but this is the cost of running a workhorse like the F-250.

Air/Fuel Ratio Differences

A proper fuel to air ratio is important to proper engine performance. The Stoichiometric mixture refers to the ideal fuel to air ratio where all the fuel is burned with no excess air. For gasoline engines, this ratio is 14.7:1, which means that there needs to be 14.7 parts air to every 1 part fuel. Diesel engines have a lower rating of 14.5 to one, which means that less air is needed to burn off all the fuel than with gasoline engines.

Weight Differences Between Engine Parts and the Engines

Diesel engines are big. In terms of displacement, the 6.7 Powerstroke diesel is larger than the 6.2-liter gas engine. It is also noticeably larger dimensionally. Just taking a peek at the engine you can tell the difference between the two based on size alone. The parts used on either engine will also vary in size as well, and the parts used on the gas engine are smaller than those on the diesel.

This will translate to some questions for engine builders. They will be wondering how well their equipment will perform on account of this weight difference. The 6.2-liter engine weighs in at around 600 pounds where the 6.7-liter diesel weighs in at over 850 pounds.

That 250 pounds is a big difference in terms of weight and can be very intimidating. Will it break your engine stand? No, not if you have a strong enough stand. You will want to make sure the base on the stand is sturdy as the added weight will make it easier to tip over. Can your engine hoist handle this extra weight? Yes. Most cherry pickers are capable of lifting 2-tons, which is still more than quadruple the weight of these engines.

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