Diesel 101: What's the Difference Between Diesel and Gas

Vince Lombardi, the famed Green Bay Packers coach, began each year's training camp with the same opening line. "Gentlemen, this is a football."

The point he made was that you are never too old or experienced to be reminded of the fundamentals now and then. How to hold a football, how to run with it, how to recover a loose ball... it's all pretty basic, but Lombardi believed this annual ritual was essential for success.

That anecdote is what came to mind when I saw the Florida News Times story this past weekend, What Is the Difference Between Diesel and Gas? It's not a clickbait title, just a straight up presentation of basic but useful information. "Just the facts, ma'am."

The story has a great opening line: "Did you know that diesel can give you 12% more energy per gallon in comparison to gasoline?" 

There are probably a lot of people who don't know that, so it serves as a nice attention getter. The question suggests that if you read this article maybe there will be other things you didn't know. Here's an overview of this piece, along with a link at the end so you can read it in its entirety.

The first decision most people make is deciding what type of vehicle they want, whether a car, sedan or truck. The next question ought to be whether to go diesel or gas power. To make this decision it helps to know how internal combustion engines work, whether gasoline powered or diesel.

Air enters the engine and mixes with fuel where it is compressed in the combustion chamber (cylinders) and ignited. The explosion pushes the piston and crankshaft which turns the gearbox. When the piston returns to its starting position the spent gases get pushed out into the exhaust system.

The difference between an engine powered by gasoline and a diesel engine takes place at the point of ignition. In a gasoline engine a spark ignites the fuel. In a diesel engine there are no spark plugs. Rather, ignition occurs by means of compression of the air-fuel mixture. High compression produces heat which generates spontaneous ignition.

Because diesel fuel produces more energy per gallon, it is more cost efficient. For this reason the engine of choice for people who do a lot of highway travel is often diesel. They also have more torque, so they accelerate faster.

The article notes that not all diesel fuel is created equal, however. Black diesel, biodiesel and other diesel fuels may detract from performance.

Some people are unaware of the differences between the two kinds of engines. Diesel engines are more durable and last longer. They used to be quite a bit heavier, but new manufacturing techniques and materials have addressed this. Because they have fewer parts, diesel engines have fewer components that can fail, which translates into fewer repairs.

Two primary drawbacks for diesel engines used to be how noisy they were and the black smoke they belched. These issues have also been addressed and are no longer the issues they once were.

Fuel Efficiency
Diesel tend to offer better fuel efficiency. This is due, in part, to the manner in which diesel engines work. Gasoline engines have a lower compression ratio in order to avoid self-ignition. In diesels, compression stroke only compresses the air because there is no fuel injected during the intake stroke. The greater compression ratio enables greater fuel efficiency.

Because of the different systems for combustion, the fuels are different. Both originate as crude oil extracted from the ground. The difference is in the refining. Diesel fuel is heavier and has a higher energy density. It also takes longer to evaporate.

Biodiesel is different from the diesel fuel refined from crude. It's important to know that diesel and biodiesel are not interchangeable. If you plan to use biodiesel, there are some changes necessary. The author doesn't detail these, so you will have to consult your mechanic.

The author ends his story by repeating the earlier assertion that diesel engines are more reliable. He adds that when things do go wrong they are usually not as expensive to fix. The article ends with a question: Are you ready to make the shift?

Ironically, right after reading this article I saw another about a diesel owner named Carl who did make a mistake and it proved very expensive. The title of the story, which you can read here, is Anyone Can Make A Mistake.

And what was the mistake Carl made? On a camping vacation, after a long day's drive, he pulled into a filling station before heading to the campground. Whether from being tired, or just the habit of filling the tank without thinking about much, he absent-mindedly filled up with 87 octane gasoline instead of diesel fuel. Oops.

An expensive mistake indeed. According to the article the final tab to fix this fiasco was $22,000. Fortunately he had good insurance, which covered most of the cost. You can be sure that this was not the kind of drama he needed for his vacation.

You can read the Florida News Times story here.

A Diesel Anecdote, Plus a Little Advice from Forrest Gump

No question about it, the film Forrest Gump was a major achievement for Hollywood as well as for its star Tom Hanks. It was one of the most original and memorable films of 1994. 

The story followed the life of Forrest Gump, a slow-witted but kind hearted man whose life intersected with many historical moments in U.S. history. Borrowing a technique employed by Woody Allen in his short feature Zelig, in a number of scenes we see Gump is inserted into real footage from history, interacting with U.S. presidents JFK, LBJ and others. 

Woven throughout the film are various pearls of wisdom delivered by its hero. You've likely heard, "My mama said 'Life is like a box of chocolates. You never know what you're gonna get." 

Forrest Gump has a masterful and entertaining way of presenting valuable life lessons. Many of them are delivered as proverbial insights from Forrest's mother (Sally Field) whom he loves to quote. For example, several times in the film Forrest is asked if he were stupid. Gump replies, "My mama says that stupid is as stupid does." What she meant, and we need to learn, is that a person should be judged by his or her actions.

Stupid Is As Stupid Does

The Colonial Pipeline ransomware hack earlier this month hit the Southeast like a jackhammer. In parts of the Southeast 85% of the gas stations were out of gas. The Colonial Pipeline runs from Texas to New Jersey and supplies 45% of the fuel to this region. As of yesterday, two-thirds of all gas stations in Washington D.C. were empty.

Against this backdrop we came across a story that shows how dangerous it is to rely on advice you find on social media. The article appeared in USA Today's Fact Check column. It's titled, Fact Check: Watered-down diesel can't be used in a gas-powered engine.

This attention-grabbing headline implies that someone actually said you can do this. So I read further.

As you can imagine, people were panicking last week because of the fuel shortages. Some of these who looked online for solutions came across a post on Facebook that read, "Remember, if the station is out of gas you can put diesel in your car as long as you water it down."

What!!!?

To make matters worse, the post was shared 1800 times. Perhaps it was shared as a joke, but if someone actually attempted to implement this advice, they would be in a serious quandary. First, the USA Today piece explains, "diesel fuel is thicker than gasoline and can damage components in a gas-powered vehicle. Adding water doesn't help, though, and does its own harm."

No kidding. As the article goes on to note, just as water and oil don't mix, neither does water and diesel fuel. Inside the tank, the water will settle to the bottom and rust your fuel tank.

For the record, gasoline and diesel fuel don't mix either. That is why they have distinct dispensing nozzles and color schemes at the pump.

By the time you reach the end of the article they hardly have to spell it out, but they do. The claim that you can mix oil with diesel fuel is... False. 

* * * 

Related Links

USA Today--Watered-down diesel Fact Check

Washington Post Map of Gasoline Shortages

What Happens if You Put Diesel in a Gasoline Car?

A Couple of “Weight” Questions to Ponder….

Question 1: How Much Does a Gallon of Diesel Fuel Weigh?  

One U.S. gallon of automotive diesel fuel at 76 degrees Fahrenheit and standard atmospheric pressure weighs 6.91 pounds. That’s equal to 110.54 ounces or 3.13 kilograms. 

The density of fuel can change due to heat and pressure, so this number may change slightly in different environments. Colder temperatures and higher pressures increase the weight of a gallon. It doesn’t, however, change too much under normal conditions, so most would agree that the weight of diesel fuel is at approximately 7 pounds per gallon.

This fuel, which looks clear or brown in liquid form, is made by distilling crude oil at high temperatures. Diesel molecules are large yet quite compact, packing more energy into every gallon. Compared to diesel’s roughly 7 pounds per gallon, the same amount of gasoline weighs only about 6.2 pounds. While diesel fuel can release harmful substances into the air when burned, it’s more fuel efficient.  

Question #2: Is the “The Weight” one of the greatest songs in music history?  

This 1968 song, widely accredited to Robbie Robertson of The Band, defies genre, and it doesn’t need one. The song is about a lone traveler’s encounters with several interesting characters in a town called Nazareth, while on a mission to send regards for a woman named Fanny. You can hear country and hear rock and hear blues and hear folk. More importantly, as you listen you understand and feel the journey it takes you on. 

The Weight is filled with really enjoyable instrumentals, biblical undertones and exchanges between the traveler and the town’s characters that leave one wondering. It is masterful storytelling paired with one of the more memorable musical sounds ever recorded.

* * * 

Here's the song itself. 

The album it appears on was included in the book 1001 Albums You Must Hear Before You Die.