Once the Biodiesel is washed and the water removed, it needs to be filtered down to at least 10 microns (preferably 5 microns) to remove all potentially damaging impurities.   I use a 10 micron water block filter from Northern Tool along with a 5 micron water filter.  I use a small 12 volt pump to move the Biodiesel from my tank through the filters into clean 5 gallon carboys.  It is then ready to go in my car! 

Cold weather:

In the winter, if the temperature gets below freezing, I add some diesel anti-gel.  There are several which may reduce the gel point by a few degrees.  I use the white bottle from Power Service, although they also have one called Arctic Express that is supposed to work for Biodiesel.   Dr. Dan at Fuelwerks recommends adding 20% regular diesel if the weather:  “if you’re not going to be using your vehicle, it won’t generate any heat.  Therefore to prevent it from freezing up, you may want to add some petro diesel to your tank (20% should be sufficient).  Also, if you have a truck (such as a Duramax or SPRINTER), your fuel tank is more exposed to the cold.  For this we recommend blending in 20% diesel or more.  As always we recommend filling up from a high-volume retailer of diesel.  A busy truck stop is a good example.  Look for a filter on the side of the pump.  If there isn’t one visable, ask them to install one.