Biodiesel starts forming wax crystals at its cloud point and stops flowing at its pour point, and the parent’s table puts the cloud point at 12-16°C for tallow, 8-12°C for lard, 0-2°C for sunflower and soybean and -3 to 0°C for rapeseed. Fuel filters block at the cloud point, which is above the pour point, so measure your own batch with a chill test, and in cold weather blend with petroleum diesel, choose rapeseed, insulate and warm the fuel.
Part of Biodiesel Production
Cold-weather performance is how biodiesel behaves as temperature falls: wax formation, filter plugging and the fixes.
The Parent’s Table And What It Cannot Tell You
| Feedstock | Cloud point (°C) | Pour point (°C) |
|---|---|---|
| Rapeseed/canola | -3 to 0 | -9 to -15 |
| Sunflower | 0 to 2 | -6 to -12 |
| Soybean | 0 to 2 | -4 to -8 |
| Tallow | 12 to 16 | 8 to 12 |
| Lard | 8 to 12 | 4 to 8 |
These are the parent’s figures; the corpus gives no source or test method for them, and real values depend on the oil’s mix of fats, how thoroughly the batch was made and what it was blended with. The pattern is reliable: the more saturated the fat (tallow, lard), the earlier the wax forms; the more unsaturated (rapeseed), the later.
Two temperatures matter. At the cloud point the first fine wax crystals appear; the fuel filter collects them and, as more form, blocks, so an engine can starve well above the pour point. At the pour point the fuel will no longer flow. Plan the lowest operating temperature at the cloud point, not the pour point.
What You Need
- A clear test tube or small jar of fuel, and a thermometer
- A cooling bath: a tub of ice and water, and for colder tests ice with salt (colder than ice alone)
- A second thermometer in the bath
- A log
Method: Find Your Own Cloud And Pour Points
Step 1: Fill the jar half full with clear, dry fuel and suspend the thermometer in it.
Step 2: Place it in the bath. Cool slowly, a degree or two at a time, and watch against light.
Step 3: Note the temperature at which the first haze or fine specks appear (cloud point).
Step 4: Continue cooling, tilting the jar every degree, until the fuel no longer moves when tilted (pour point).
Step 5: Record both against the batch’s feedstock. Repeat on each new feedstock or blend.
Fixes
- Blend with petroleum diesel (the parent’s B50 is a 50% blend), if you have it; the blend’s cloud point must be measured, not assumed to lie halfway.
- Choose rapeseed if the climate is cold (the parent’s lowest gel point), but check its yield claims on Oilseed Crops.
- Blend animal-fat biodiesel with vegetable-oil biodiesel, the parent suggests 50/50.
- Insulate fuel lines and tank, and keep the engine warm between uses (parent).
- Fit a filter heater or a tank warmed by engine coolant, if the engine design allows.
- Store the fuel in a warm place.
For plain petroleum diesel, the corpus advises kerosene as a blending agent against waxing (Diesel & Heating Oil); it does not say whether this works with biodiesel, so test it.
Worked Example: Blend Check
A tallow biodiesel clouds at 12-16°C. Mixed 50/50 with a rapeseed biodiesel clouding at -3 to 0°C, the blend does not cloud at the average: for a mid-range 14°C and -1.5°C, the simple mean is 6.3°C, but blending is not linear, and the true cloud point is usually closer to that of the waxier component (a recalled behaviour, not a sourced figure). So a 6.3°C estimate is optimistic and the batch must be measured with the chill test before you rely on it in winter.
Common Mistakes
- Using the pour point as the limit. The filter blocks first.
- Assuming the table applies to your batch.
- Leaving fuel in an unheated tank overnight in the first cold snap.
Cold tests and winter fuel
Ice-salt baths cause cold burns on bare skin; wear gloves. Never warm fuel with a naked flame or over a fire; use hot water or the engine’s own heat. Chilled fuel jars with methanol residues from poor washing are a fire risk if you warm them near a heater.
What’s Next
- Learn next: Quality & Testing
- Combine with: Animal Fats, the feedstock with the worst cold behaviour