Biodiesel in Winter

By Rick Da Tech


Making and using biodiesel in the winter is just a little more complex than making and using biodiesel in the summer. That is because biodiesel like all diesel fuels tends to gel up and can clog up filters and plug fuel lines in cold weather. Fortunately, we can test our biodiesel to determine how well it will perform in cold weather.

Cloud Point and Pour Point

Cloud point and pour point testing biodieselAs the temperature drops, biodiesel will start to gel up 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 two are testing for Cloud Point and Pour Point.

Cloud Point is the temperature at which the crystals of solid biodiesel first become visible. As the biodiesel starts to freeze, it will form small crystals that start clumping together. They will become visible as cloudy biodiesel when they grow to four times larger than the wavelength of visible light. At this size the crystals will easily pass through filters and can be pumped and used with no problems. As the biodiesel gets colder, the crystals get bigger and will eventually plug filters.
Pour Point, or Gel Point as it is called by some home brewers, 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 Gel 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 1C increments for cloud point. Once you have the cloud point, inspect it at 3C increments to determine when it gels up for the pour point.

Generally most of your biodiesel made from the same oil source will have similar cloud and pour points. So most hobbyists don't test every batch, instead, we will put a quart to a gallon of the same fuel we have in our tank in a glass jar and sit it next to our vehicle. Inspect it in the morning to see if it's reached either the cloud point or pour point.

Making winter biodiesel

Use the right oil

The most important property of oil that determines the cold weather performance of biodiesel is its saturated FFA content[1]. The more saturated fatty acids there are in 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 fatty acid composition of the feedstock oil used to make it. So, picking oil with a low saturated fat content is critical to making cold weather biodiesel. Canola Biodiesel is one of the lowest cloud point biodiesel’s because Canola Oil is very low in saturated fatty acids. While peanut oil biodiesel is relatively high in saturated fats and therefore 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 will be.

I can't stress this one point enough. The most important thing you can do when making winter biodiesel is starting with the right oil. The less saturated fat content, the better.


Nutritional Makup 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.


Ultra Low Gel Point Biodiesel via Urea Clathration

Urea Clathration: Ultra Low Gel Point Biodiesel

Urea Clatheration is one way chemistry can remove the saturated fatty acids from biodiesel and acheive a pour point of -65°F. Even though it works, it is probably not something a biodiesel hobbyist would use in production because it is complexity. 



Cold Soak Filtration Test

As far back as 1995 homebrewers were noticing that when b100 frozen 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 120F 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 before it was used.

The commericial biodiesel world ran into this problem with blends when Minnesota mandated a 5% biodiesel blend for all biodiesel sold in the state. 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 could be formed above the cloud point temperature. The latest 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. These crystals then change form to a more stable, less soluble crystal with light warming rather than dissolving back into solution. The Cold Soak Filtration Test came about as a direct result of filter plugging in Minnesota.

The Cold Soak Filtration test cools a biodiesel sample to 40F and holds 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 in a specified length of time. A 300ml sample must pass through a specific 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 the Cold Soak Filtration Test, did not experience filter plugging above the cloud point. Biodiesel that took longer than 200 seconds started plugging filters at temperatures above that predicted by its cloud point alone.

Cold Filtering Biodiesel

  • Cold filter or cold settle feedstock oil. This is 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. This promotes the precipitation of waxes while keeping biodiesel liquid. Then filter or siphon off the liquid on top.
  • Cold filtering finished biodiesel before blending. Chilled to -3C then filtered through cold wood chips. 

Pour Point Depressing Additives

Research has shown that Cloud point predicts the cold filter plugging point than pour point. There are two ways to lower the Cloud Point of your biodiesel, you can blend it diesel, or you can add in additives that prevent the formation of solid crystals. The most effective is a combination of both blending and adding additives.

The University of Idaho tested four different biodiesel pour point depressing addities. 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. Blending to B20 lowered the cloud point by 13 deg C. But, they were only able to lower the cloud point by about 1 deg C by putting additives in B20. They were able to lower pour point of biodiesel by 15C just by blending it to B20. The four additives then lowered the pour point of B20 by another 10 to 20 degC. The LSU website reports that blending good quality B50 canola biodiesel can easily reduce the cloud point from 27F to 18F or from -3C to -7C.

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

Other pour point depressing additives:


Using Biodiesel in Winter

Using Biodiesel in cold weatherPreventive Maintenace

Diesels need some basic fall time maintenance to prepare them for winter, these same preventitive 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 diesels running on biodiesel. As part of general diesel vehicle maintenance, make sure your batteries are in good shape. When batteries get cold, they can’t 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 like 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 blend with diesel. The exact blend will be 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 gel point a little more. Even if you know the cloud point and pour point of your biodiesel, it’s still a good idea to keep a mason jar filled with the same blend you have in your vehicle outside so you can 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’re not using it. If you don’t have a garage, park next to a wall, anything to protect it from the cold weather. The colder your engine is, the harder it will be to crank. Cold oil, cold coolant, cold battery, and cold combustion chamber make it that much harder to crank. 

In Northern areas, diesels will come new with some type of 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's not running. Most use household electricity to power the heaters. There are block heaters that are mounted in the block and heat the coolant. There are coolant heaters that heat your coolant outside the block and pump it through 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. Dip stick heaters let you warm up your oil by replacing the oil dip stick 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 will have a third less cranking power than a warm battery. There are two styles of battery heaters, both of which use household electricty 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 12VDC. 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


Biodiesel Fuel Management in Cold Weather - LSU Ag Center

Impact of addItIves on cold flow propertIes of bIodIesel - University of Idaho Biodiesel Tech Note

Biodiesel Cloud Point and Cold Weather Issues - 

Cold Flow Backgrounder - National Biodiesel Board

Great Infopop thread on making and using cold weather biodiesel

REG Fuel cold fitering patent 

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