The patent for the invention of the diesel engine was given to Rudolph Diesel in 1889. Diesel engines use compression to ignite the fuel, unlike a gasoline engine that has an ignition system using spark plugs. That first diesel engine was fueled by diesel made from peanut oil; basically the first diesel fuel was a biodiesel. These days there are two major types of diesel fuel: petroleum based, which is refined from oil; and biodiesel, which is made from organic materials, corn, soybeans, and waste from packing plants.
Petroleum diesel is refined from crude oil using three processes: separation, conversion and purification. Separation takes place in large distillation towers. The oil is exposed to extreme heat, causing it to separate into gases and liquids. The different products from oil are separated based on the temperature differences between the top and bottom of the tower, gases to the top, and liquids toward the bottom. Conversion usually involves applying a catalyst to some of the heavier oils to create more gasoline, diesel, and propane. Purification, the final step, usually exposes the products to hydrogen and a catalyst to remove sulfur.
Biodiesel is refined from plant and/or animal oils or fats that are then mixed with alcohol, typically methanol, and a catalyst. Heating the mixture causes it to react, transforming the fat into glycerin and biodiesel. Excess methanol is removed before more purification and maybe distillation to remove any unwanted color.
We know how diesel is made or refined and where it comes from. So why use diesel engines instead of gasoline? We use diesel engines in trucks instead of gasoline partly because they are up to twice as efficient as a gasoline engine. That means you can do more work with the same amount of fuel. There are reasons for this, no spark plug allows us to compress the fuel much more, and more compression means the fuel will burn more completely with the air in the cylinder, releasing more energy. Diesel engines need less fuel when working at lower power levels, a gasoline engine needs less air or more fuel to keep the cylinder working unless it's at full power. Diesel has more energy per gallon than gasoline. Diesel is a better lubricant than gasoline so a diesel engine will naturally run with less friction.
How many types of diesel fuel are there? There are five types of diesel, 1D, 2D, 4D, Biodiesel, and Synthetic diesel. The most common is 2D, used in warmer weather and can be mixed with 1D for winter use. 1D has only about 95% of the energy that 2D has, this causes lower fuel mileage and lower power. 4D is most common in low RPM stationary, locomotive and marine applications. Biodiesel can and is most commonly mixed with petroleum diesel as a blend, B5, B15, and B20. The number behind the B is the maximum percentage of biodiesel in the mix. Synthetic diesel is made from many carbon-based sources such as wood, straw, corn and even garbage and food scraps, not found easily in the commercial marketplace. 
There is a problem diesel has that gasoline doesn't have, the gelling in cold weather issue. Why does diesel gel? Diesel fuel contains paraffin wax in two forms, liquid wax in suspension in the fuel and wax seed crystals that are floating throughout the fuel. When the wax in the fuel has begun attaching itself to the wax crystals making them large enough to see, this is called the Cloud Point. When the temperature is above the cloud point, the wax crystals cannot be seen without a microscope. When the temperature gets colder, the wax crystals will get larger and start to stick to each other. This is the Cold Filter Plug Point or Gel Point. Now is the time the fuel has difficulty passing through filters and the engine will starve for fuel and die. If the temperature gets cold enough the fuel can become semi-solid, it cannot be poured, this point is called the Pour Point.
What do we do if we start to gel or if we know we are going into an area that the temperatures are going to be lower than the fuels gel point? Simply put, treat the fuel. There are three ways to prevent the fuel from gelling, 1. Keep the fuel above the gel point. Difficult if not impossible when runs take us into temperatures that are below the gel point. 2. Blend 2D diesel with 1D or kerosene, kerosene has less wax spreading it thinner within the mix. With Ultra Low Sulfur Diesel being unreliable as to it's cold properties, the need to blend large volumes of special Ultra Low Sulfur Kerosene could be cost prohibitive. 3. Use a Cold Flow Improver or Anti-Gel to keep the wax crystals from sticking together and growing. This can be done at a reasonable cost and is done reliably. These products are a co-polymer that coats the paraffin wax crystals to prevent them from sticking together. One thing to remember is that the fuel must be treated before it begins to gel, once it has gelled the additive won't mix into the fuel and do it's job until the fuel has thawed.
If you have gelled and are shut down, there is two ways to get going again. 1. Pull the vehicle into a shop or some place warm for the fuel to thaw, not a good option for most of us. 2. Use a product designed to dissolve the wax and re-liquefy the fuel can be done economically and is the best option for most of us. To get going again replace the fuel filter with a new one filled with 50% warm fuel and top off with the un-gelling product of your choice. If you must reuse the gelled filter, dump as much of the gel out and refill with a 50/50 mix of fuel un-gel product. Treat the fuel tanks as directed on the label of the bottle, if your tanks are low estimate how many gallons are in them and treat accordingly, wait 20-30 minutes to allow the treatment to work, the engine should start. Allow the engine to warm before driving. Over treating can be as bad as not treating at all, maybe worse as far as fuel system damage is concerned.
If you are gelled DO NOT use gasoline, ethanol or any kind of alcohol, as it will lower the flash point of the fuel and will likely cause damage to the fuel pump and injectors.
Most truck stops treat their fuel for the weather conditions they have in their area, so self-treating may not be needed. Ask your fuel supplier how the fuel is treated. If you fuel in the south then head north, be prepared to treat for the weather conditions you are headed into, and treat your fuel as needed. If you fuel in the north and head south, you're good to go most likely.   

Comments (5)

Read These Next...



August 25, 2015


Bob's expertise is great for a science/history geek like myself! From a guy who thrives on things like the shows "How It's Made" and "How Do They Do That", this is right up my alley. Thank you for the insight on the fuel that makes us go!

January 18, 2014 7:36:06 AM

We are lucky to have Bobs many years of experiance as a mechanic . Great detailed blog.

January 18, 2014 7:19:26 AM

Very well written article Bob. Very informative and hopefully people will take notice and properly prepare for the cold climates!

January 17, 2014 19:33:12 PM

Thanks Bob I learned a lot about fuel!

January 17, 2014 13:47:59 PM

Great info Bob. It will definitely make me think about putting enough fuel in up north to get to the south to fuel up and vice versa. I tend to be conservative and buy my fuel up north. Increasing my fuel mileage is important.

January 17, 2014 5:54:09 AM