Cloud Point and Pour Point Tests
By Rick Da Tech
When it gets really cold, biodiesel can start to gel up, plugging fuel 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 (CP) and Pour Point (PP).
Cloud Point is the temperature at which the crystals of solid biodiesel first become visible. As the biodiesel 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. At colder temperatures, the crystals grow to the point that they plug filters.
Pour Point, or Gel Point as home brewers call it, is the temperature where biodiesel becomes solid and no longer flows. Once your biodiesel reaches the pour point temperature, it is well past the Cold Filter Plug Point, making Cloud Point the most important temperature for cold weather biodiesel.
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. If the biodiesel does not gel up in the refrigerator, move it to the freezer and continue checking it on a regular basis until it gels up.
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. Inspect it in the morning to see if it reached either the cloud point or pour point.
Biodiesel Cloud Point and Cold Weather Issues - www.extension.org