Gelling – What It Is and What To Do About It.
Diesel fuel contains paraffin wax in two forms, liquid wax that is in suspension in the fuel and wax seed crystals that are floating throughout the fuel. In temperatures above the fuel’s Cloud Point (CP), you can’t see wax without a microscope. When fuel reaches its Cloud Point, wax in the fuel has begun attaching itself to the wax crystals making them large enough to be seen with the naked eye. This wax will appear as a cloud-like formation floating in the fuel. As the fuel temperature drops, the wax crystals continue to get larger and will begin to further stick to each other. At this Cold Filter Plug Point (CFPP) or Gel-Point, the fuel will have difficulty passing through fuel filters. This is the critical point at which it can become difficult or impossible to operate an engine or burner. As the temperature continues to drop the fuel can become a semi-solid, this is known as the Pour Point (PP), or the point at which fuel will no longer pour. “Gelling” occurs when diesel fuel reaches its Cold Filter Plug Point.
You can prevent from fuel from gelling in three ways:
- Keep the fuel temperature above the CFPP,
- Blend with a fuel such as kerosene that has less wax in order to spread out the wax and wax crystals,
- Use a Cold Flow Improver (or “Anti-Gel”) to prevent the wax crystals from growing and the wax crystals from sticking together.
#1 can be difficult if not impossible. #2 can be very expensive and reduces your fuel’s lubricity and BTUs (see our article covering ULSD for more information on kerosene). #3 can be done reliably and inexpensively, and is the best way to deal with these issues.
Cold flow improvers or “anti-gels” are a co-polymer that coats the paraffin wax crystals normally found in all diesel fuels in order to prevent the wax crystals from getting any larger and sticking to each other (gelling). This anti-gel material is quite thick and must be blended with solvents to allow it to be mixed properly with fuels. It is important to understand that even anti-gels blended with solvents will thicken at temperatures below 40°F. Fuel additives containing anti-gel should be stored above 40°F. If stored below 40°F allow them to warm up before adding them to the fuel.
An analogy of what happens to anti-gel is what happens with coolant antifreeze. By itself, antifreeze will thicken in cold weather to the point of being nearly solid, but when mixed with the correct amount of water it will prevent freezing to -40°F or more. Anti-gels work in a similar way – when mixed with the correct amount of fuel they effectively prevent gelling, lowering the gel point by as much as 40°F (found in Complete Fuel Treatment™).
Another important thing to remember about anti-gel additives is that you must treat the fuel before it begins to gel. Products such as Complete Fuel Treatment™ are preventatives designed to prevent gelling, but once the fuel has gelled, anti-gels won’t help you until the fuel has thawed.
If someone tells you they have an anti-gel additive that does not thicken in temperatures below freezing, you should know and understand that there are two types of additives that don’t have this problem, one doesn’t actually contain any anti-gel, the other contains a smaller amount of anti-gel with large amounts of alcohol to prevent thickening. Alcohol is one of the worst things to put in an additive.
If your fuel is already gelled, see our article on reliquefying already gelled fuel.