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Help Me Understand How Diesel Fuel Prolongs My Tractor Engine Life

We want to teach you everything you need to know about tractor diesel fuel.

Diesel engines, as a source of power, are some of the most economical, dependable, and long-lasting systems available.

What exactly is diesel fuel?

Diesel fuel is a petroleum-based, less-refined cousin to other common fuels such as gasoline, jet fuel, and kerosene. Compared to gasoline, diesel is oilier and heavier, evaporates slower, and has a boiling point higher than water.

A gallon of diesel contains 147,000 BTUs vs. 125,000 BTUs for gasoline.

Ignition in a diesel engine takes place due to high compression, in concert, with the injection of the fuel. It does not need a spark like a gasoline engine. A diesel engine is also highly efficient when throttled down. The air intake is not throttled down like its gasoline counterpart.


Diesel fuel contains paraffin wax.

Paraffin increases the cetane number (CN) or content. Cetane is a measure of a fuel’s ignition delay. The benefit of cetane in a diesel is like the performance benefit that increased octane brings to a gasoline engine.

The minimum cetane requirement in the United States is CN40. Higher CN improves engine starting --- especially helpful in cold weather. The primary diesel blends are No. 1, sometimes called 1D, and No. 2, sometimes called 2D. No. 2 is considered a summer grade. As cooler weather approaches, distributers change to a winter blend of No. 2 and No. 1.

Fuel stations offer two kinds of diesel fuel. Some mix No. 2 with No. 1 kerosene. This is a more refined fuel (and more expensive) to make what is known as a winter blend or winter diesel. Other stations may even give their customers a choice of making their own blends. Buyer beware. Winterized diesel is better for today’s complex fuel systems. It contains fuel system-healthy additives straight from the refiner. Winterized fuel also costs less to produce.

Since diesel fuel contains wax, it is important that a summer blend not be used during the fall-winter-spring cold weather times. A summer blend will begin to have the wax precipitate out around 32F. This first point is known as the cloud point, where the fuel begins to look cloudy.

As temperatures drop, those solidifying wax particles combine into solids that become large enough to clog filters. This second point is known as the pour point (or gel point), in which so many larger wax particles are present. When this happens, the fuel no longer flows. The gel point is generally 10-15 degrees lower than the cloud point. Kerosene additions lower the gel point. Winterization levels vary across different parts of the country and can range from 10F to as much as -20F --- though no real published rating system is in effect or enforced.

Water Issues

Diesel fuels have some water suspended in the mix.

At the point that the wax begins to precipitate out, any water held in suspension will begin to form ice crystals. Put the two together and you have a major problem that can extend from the filter, through the lines, and into the tank.

Diesel fuel is relatively free from water from the refinery.

Water enters the mix in a variety of ways. These include atmospheric variables, free water settling, the delivery process, condensation, and leakage. Generally, these are handling issues. If you are receiving bulk fuel, ask to be the first delivery. This way there is less chance of getting water and/or contaminants that have settled to the bottom. The installation of a water removal system at the tank inlet is also effective.

Minimizing atmospheric contamination is important. You can keep a sealed cap on the tank, can, and/or tractor. If you are in an area with large temperature swings and high humidity, a water separator is a great line of defense. The key is to keep the water content below the saturation point.

Zero water in diesel fuel is optimum --- just not practical. Keeping the water content below the saturation point is key. To measure water content, a variety of methods can be employed such as an outside lab, water monitors (sensors), and titration testing, using the Karl Fischer methodology.

To test to see if water settled at the bottom of a tank, a simple dip test can be effective. It requires a stick or weighted string to be coated with water indicating paste and lowered into the tank. If excessive water is found, the tank will have to be drained. You do not want the water to reach your fuel injection system.

Organic Contaminants

You also need to watch for fungi and bacteria.

They also like the moist, cool storage environment.

Fungi and bacteria lead to acids and corrosive by-products, that over time, will damage tanks.


It is important to prevent any fuel-related issues.

Here are some recommendations.

Purchase fuel from a reliable distributor.

Use fuel in a timely manner. Even under the best conditions, fuel has a shelf life of 6 months before degradation occurs.

Keep your cans, storage tanks, and tractor tank sealed.

They should always be clean and free from contaminants. Use a funnel filter while fueling.

When idle, store your machines indoors.

Many garages and barns are not heated. Draping a tarp over the tractor and placing a heat source, such as a trouble light, near the lines, and filter can be helpful. Just do not create a fire hazard.

Use seasonal fuels.

Utilize summer fuel in the summer and winterized fuel in the winter. Additives with cetane boosters can raise or lower the gel point protection.

Check your owner’s manual for the manufacturer’s recommendation.

Beware of light, air, and water.

Use preventative care, as discussed, from the start, to protect your fuel system and keep it running well.


There are also bio-diesel and bio-fuels. Those alternatives will be discussed in a separate, dedicated article. When it comes to these options, please check your owner’s manual, and consult your tractor dealer.

If you need any further help or have any questions about diesel fuel, tractors, or anything else, please contact your dealer, local mechanic, or call us at 602-734-9944. Please ask about our current new and used tractor supply.

Team Tractor and Equipment - #1 Tractor Dealer in Arizona. We sell and service most major brands of tractors including Yanmar, Kubota, John Deere, TYM, Mahindra, Kioti, Case, New Holland, Massey Ferguson, Ford, Deutz, Case IH, Farmall, International Harvester, Branson Tractors, LS, Shibura, Claas Tractor, McCormick Tractors, Valtra, Solis, YTO, Montana, and Nortrac.

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