Normally you can use pure ecodiesel or a mixture of ecodiesel and petroleum diesel as a fuel in any unmodified diesel engine. There are two situations in which you definitely should mix ecodiesel with petroleum-based diesel.
- If you are going to be running the engine at a temperature lower than 55° F (13° C), you should mix ecodiesel with petroleum diesel. A 50:50 mixture will work for cold weather. Pure ecodiesel will thicken and cloud at 55° F, which could clog your fuel line and stop your engine. Pure petroleum diesel, in contrast, has a cloud point of -10° F (-24° C). The colder your conditions, the higher percentage of petroleum diesel you will want to use. Above 55° F you can use pure ecodiesel without any problem. Both types of diesel return to normal as soon as the temperature warms above their cloud point.
- You will want to use a mixture of 20% ecodiesel with 80% petroleum diesel (called B20) if your engine has natural rubber seals or hoses. Pure ecodiesel can degrade natural rubber, though B20 tends not to cause problems. If you have an older engine (which is where natural rubber parts are found), you could replace the rubber with polymer parts and run pure ecodiesel.