Biodiesel in Winter



Making and using biodiesel in the winter requires a little more care than making and using biodiesel in the summer. Biodiesel like all diesel fuels tends to gel in cold weather, resulting in clogged filters and plugged fuel lines. Fortunately, we can test our biodiesel to determine how well it performs in cold weather.

Cloud Point and Pour Point

Cloud point and pour point testing biodieselAs the temperature drops, biodiesel starts to gel, which can clog filters. The temperature where this happens is called the Cold Filter Plugging Point (CFPP). This temperature varies depending on the properties of the oil and the processes used to make biodiesel. Unfortunately, CFPP is nearly impossible for biodiesel hobbyists to determine at home. You can send your biodiesel off to have it tested, but this can get expensive. So, there are two tests that we use to help estimate the lowest temperature we can use our biodiesel. These are testing for Cloud Point and Pour Point.

Cloud Point is the temperature at which the crystals of solid biodiesel first become visible. As it starts to freeze, it forms small crystals that start clumping together. They become visible as Cloudy biodiesel when they grow to four times larger than the wavelength of visible light. At this size, the crystals easily pass through filters and can be pumped and used with no problems. These crystals grow larger as the temperature drops. Eventually, the crystals grow large enough to plug filters.

Pour Point, or Gel Point, as some home-brewers call it, is the temperature where biodiesel becomes solid and can no longer be pumped. That temperature is a good bit colder than the Cold Filter Plugging Point.

To measure the Cloud Point and Pour Point of your biodiesel, put a sample in your refrigerator. I use a mason jar with a plastic lid, through which I stick a thermometer to measure the temperature as it cools down. You want to try to inspect it at 1°C increments for Cloud Point. Once you have the Cloud Point, inspect it at 3°C increments to determine when it gels for the Pour Point.

Most of your biodiesel made from the same oil source has similar Cloud and Pour Points. So, most hobbyists do not test every batch. Instead, we put a quart to a gallon of the same fuel we have in our tank in a glass jar and set it next to our vehicle. We inspect it in the morning to see if it has reached either the Cloud Point or Pour Point.

Making winter biodiesel

Use the right oil

The percentage of saturated fats in your oil is the property that most strongly determines the cold weather performance of biodiesel[1]. The more saturated fats in the oil used to make your biodiesel, the higher the Cloud and Pour Points. In fact, scientists can successfully predict Cloud Point, and Pour Point of biodiesel based on the composition of the feedstock oil used to make it. So, picking an oil with a low saturated fat content is critical to producing good cold weather biodiesel. Canola Biodiesel is one of the lowest Cloud Point biodiesel's because Canola Oil is very low in saturated fats. Peanut oil biodiesel is relatively high in saturated fats and has a higher Cloud Point than canola biodiesel.

Hydrogenated and partially hydrogenated oils act just like naturally saturated fats. Just like saturated fat, the higher the concentration of hydrogenated or saturated fat, the higher the Cloud and Pour Points are.

I cannot stress this one point enough; the most important thing you can do when making winter biodiesel is starting with the right oil. Less saturated fat content means lower cloud point.


Nutritional Makeup of Various Oils *



  Cloud Point  
Deg °C

  Pour Point  
Deg °C

Canola oil




Safflower Oil




Camelina Oil




Sunflower oil




Corn Oil




Olive oil




Soybean oil




Peanut oil




Chufa oil



Cottonseed Oil    




Chicken Fat







Palm Oil








Palm Kernal Oil




Coconut oil




 * note- approximated values - actual values vary depending on the individual plant and extraction methods.



Oil for Making Biodiesel

There is a huge variation in fats and oils used to make biodiesel. This article goes into the properties of the different oils to help you know which are best for making biodiesel. For instance, the saturated fat content of an oil is a strong indicator of its cold weather performance.



Cold Soak Filtration Test

As far back as 1995, homebrewers were noticing that when b100 froze and then thawed out, not all of the biodiesel would go back into solution. We found it had to be heated and mixed, sometimes up to 120°F (50°C) to get the "Dreaded White Stuff" to go back into solution with the biodiesel. The Dreaded White stuff would plug filters and strand home-brewers if not detected early enough.

The commercial biodiesel world ran into this problem when Minnesota mandated a 5% biodiesel blend. That winter, trucking companies started reporting excessive plugged fuel filters. In the months and years that followed, extensive research was conducted to determine what was causing the filters to plug and how to prevent it. What they found was that under certain conditions, filter plugging precipitants formed above the Cloud Point temperature. Research indicates Saturated MonoGlycerides as the most likely cause of that filter plugging. When biodiesel is chilled, the saturated monoglycerides can form crystals above the Cloud Point. After light warming, these crystals then change form to a more stable, less soluble crystal, rather than dissolving back into solution. As a direct result of the filter plugging in Minnesota, the Cold Soak Filtration Test was developed to detect this problem before it left the plant.

The Minnesota problem was a little different than homebrewers encountered. Blends do behave differently than B100. With B100 we were noticing small amounts of the dreaded white stuff accumulating on the bottom of storage tanks. In Minnesota however, the 5% blends were accumulating enough of the dreaded white stuff to require sending someone into the tank to shovel the stuff out as they saw large quantities of the stuff.

The Cold Soak Filtration Test calls for chilling a sample of biodiesel to 40°F and holding it there for 16 hours. It is then allowed to warm up to room temperature without heating or stirring the sample. Then the sample is passed through a filter. A 300ml sample must pass through a filter using vacuum in under 360 seconds to pass. At least one study has shown that biodiesel that took less than 200 seconds to pass sample did not experience filter plugging. Biodiesel that took longer than 200 seconds started plugging filters at temperatures above that predicted by its Cloud Point.


Ultra Low Gel Point Biodiesel via Urea Clathration

Urea Clathration: Ultra Low Gel Point Biodiesel

Urea Clatheration is a process that can remove the saturated fatty acids from biodiesel and achieve a Pour Point of -65°F. Even though it works, it is probably not something a biodiesel hobbyist would use because of its complexity.


Cold Filtering Biodiesel

There are three cold filtering methods commonly used to improve cold weather performance of biodiesel:

  • Cold filter or cold settle feedstock oil, or simply leaving the oil outside where it can freeze and melt. Then siphon off the liquid stuff on top to use for biodiesel.
  • Cold filtering finished biodiesel, after blending with diesel promoting the precipitation of waxes while keeping biodiesel liquid. Then filter or siphon off the liquid on top.
  • Cold filtering finished biodiesel before blending is chilling it to -3C then filtering it through cold wood chips.

Cold Flow Improvers

Research has shown that Cloud Point predicts the cold filter plugging Point better than Pour Point. There are two ways to lower the Cloud Point of your biodiesel. You can blend it with diesel, and, use additives. Blending with No 1 Diesel dilutes the biodiesel and puts distance between the seed crystals that form just above the cloud point. Historically, cold flow improvers for B100 did not significantly alter the cloud point. However, there are diesel fuel additives that are very effective at reducing the Cloud Point of diesel fuel. They also lower the Cloud Point of biodiesel blends by lowering the cloud point of the diesel portion of the blend.

Recently, several companies have claimed to design new additives that lower the cloud point of B100. They have identified chemicals that impact the cloud points of specific fatty acid profiles. They blend those chemicals into mixtures that are most effective on specific feedstocks, like soy methyl esters or palm methyl esters. So far, these new customized additives have been made available to the large commercial producers and blenders.

As of 2017, I have not found any cloud point depressants available for retail purchase that work on B100. There are however, several Pour Point depressing additives available for B100.

Pour Point Depressing Additives

The University of Idaho tested four different biodiesel Pour Point depressing additives. They had little to no effect on either the Cloud Point or Pour Point of B100, but all were very effective at reducing the Pour Point of blends. The researchers lowered the cloud point by 13ºC with blending to B20 and by another 1ºC with additives. Pour Point was lowered by 15ºC by blending it to B20 and by another 10 to 20ºC by adding additives.

The four biodiesel additives chosen for the study above were:

  • Flozol 503 (The Lubrizol Corporation, Wickliffe, OH),
  • Bioflow 875 (Octel Sterron, Newark, DE),
  • MCC P205 (Midcontinental chemical, Overland Park, KS), and
  • Arctic Express 0.25% (Power Service, Weatherford, TX). T

Commercially available B100 pour point depressing additives:


Using Biodiesel in Winter

Using Biodiesel in cold weatherPreventive Maintenace

Diesel vehicles need some basic fall time maintenance to prepare them for winter; these same preventative checks apply to biodiesel vehicles as well. Check your batteries and your glow plugs, make sure you have some way to keep your oil, fuel, and battery warm at night.

Check your batteries.

Winter is hard on diesel vehicles in general and especially so for one running on biodiesel. As part of general vehicle maintenance, make sure your batteries are in good shape. When batteries get cold, they cannot deliver as much power as when they are warm, and in cold weather, we demand more out of our batteries than at any other time.

Check your glow plugs.

Make sure your glow plugs are in good shape. Even one inoperable glow plug can prevent the engine from cranking in cold weather. If the engine is hard to start, or the glow plug indicator light on the dash does not come on as it should, then take the vehicle to a good diesel mechanic and have them check out the glow plugs.

Know you biodiesel

You should have a pretty good idea of at what temperature you can expect your biodiesel to Cloud up and gel. Keep an eye on the weather. If it is going to get colder than your biodiesel can take, then you should blend with diesel. The exact blend is determined by the cold flow properties of your biodiesel, how cold your winters get, and the cold flow properties of the diesel fuel you blend with it. Pour Point depressing additives can be added to biodiesel blends to lower the Pour Point a little more. Even if you know the Cloud Point and Pour Point of your biodiesel, it is still a good idea to keep a mason jar next to your car filled with the same fuel you have in your tank. Be sure to inspect it in the mornings before you try using your vehicle.

Keep it warm.

A heated garage is the absolute best place to put your diesel vehicle when you are not using it. If you do not have a garage, park next to a wall, anything to protect it from the cold weather. The colder your engine is, the harder it is to crank. Cold oil, cold coolant, cold battery, and cold combustion chamber all make it harder to crank.

In Northern areas, new diesel vehicles come with a block heater or engine heater. Be sure you know what you have on your vehicle. Engine block heaters are all about keeping your engine warm when it is not running. Most use household electricity to power the heaters. There are block heaters that are installed in the block and heat the coolant. There are coolant heaters that heat your coolant outside the block and then pump it into your engine. There are magnetic heaters that stick to anything steel, like oil pans and transmission pans. There are oil pan heaters that are flexible heating pads that you glue to your oil pan to make sure your oil is ready to go when you are. Dipstick heaters let you warm up your oil by replacing the oil dipstick with a heating rod that uses household electricity. Just swap them out and put the stock one back in when you get ready to ride.

Another item that works better warm is your battery. A cold battery has a third less cranking power than a warm battery. There are two styles of battery heaters, both of which use household electricity to power the heater. The battery pad, which slips under the battery and heats it from the bottom up, and the wrap style that puts out more heat for more extreme cold weather.

Fuel filter heaters are a slightly different beast. These are usually about keeping the fuel filter warm while the engine is running. There are two varieties, coolant heated and Electric. Usually, the first problem you have with cold weather when using biodiesel is plugged filters. A heated filter can help prevent that by keeping the biodiesel in your fuel filter above its Cloud Point.


Related Links

[1]Correlations of Fuel Cold Properties of Biodiesel with its Fatty Acid Composition - Graduate School of Energy Science, Kyoto University, Japan

[2]Impact of addItIves on cold flow properties of bIodIesel - University of Idaho Biodiesel Tech Note

Evonik Cold Flow Improver marketing brochure 

Biodiesel Cloud Point and Cold Weather Issues - 

Effectiveness of Cold Flow Additives on Various Biodiesel, Diesel and Their Blends  D. S. Shrestha, J. Van Gerpen, J. Thompson, 2008

Cold flow properties of biodiesel and effect of commercial additives D. S. Shrestha, J. Van Gerpen, J. Thompson, A. Zawadzki, 2005

Cold Flow Backgrounder - National Biodiesel Board

Great Infopop thread on making and using cold weather biodiesel

REG Fuel cold filtering patent