Part 1: Understanding Cloud Point and Other Cold-Weather Fuel Considerations

If colder temperatures give you pause when it comes to your fuel storage and additive choices, you’re not alone. However, it doesn’t have to be as complicated as you may think. In this three-part series, we’ll break down what cold flow properties are, what a fuel’s Cloud Point means and what you can do to keep your diesel vehicles running this winter.

What Is Cloud Point?

To put it simply, Cloud Point is the temperature at which wax crystals cause fuel to appear cloudy. You may have also heard it described as the point where fuel can begin to “gel.”

It’s important to note that as the fuel gets colder — and likely closer to its Cloud Point — it also becomes more viscous and harder to pump. This is a problem with all liquid fuels, including petroleum diesel. Sometimes increased viscosity alone can cause “slow flow” through fuel dispenser filters and make it difficult to get sufficient fuel through vehicle fuel filters to keep the engine happy. This is different from wax crystals plugging a fuel filter and isn’t a fuel property that is easy to predict from common cold property tests.

What Are Cold-Flow Parameters?*

“Cold-flow properties” is a category of tests that indicate the range of temperatures at which a fuel can operate. A few common examples are the Cold Filter Plugging Point (CFPP), Low Temperature Flow Test (LTFT) and Pour Point (PP).

The CFPP test determines the highest temperature at which a fuel filter could plug under a standard set of test conditions. The test was designed years ago to simulate the performance of an average vehicle and is still useful. However, because the filter used in the test is coarser than the fuel filters on many modern vehicles, the test might not be as conservative for some modern fuel system designs as it is for older models, which make up roughly one-third of heavy-duty vehicles and 20% of light-duty vehicles.

The LTFT — a lesser-known and -utilized test — also uses a standard set of test conditions to estimate the highest temperature at which a fuel filter might stop flowing. The difference is that this test uses slower cooling and a filter more like those in modern fuel system designs in North American heavy-duty trucks. Some people consider LTFT to be the most conservative cold-flow property test for predicting a fuel’s low-temperature operability. LTFT is not a common test because it takes a long time, is labor intensive and requires a relatively large amount of fuel (i.e., it is slow and expensive).

A fuel’s Pour Point is the temperature at which it has thickened or frozen to the point where it will no longer flow at all. This is the least conservative test, in that the Pour Point of most petroleum fuels is many degrees lower than the temperature at which a fuel will cease to flow sufficiently through a fuel filter. Pour Point is most commonly used for heating fuels (home heating oil, for example) or for determining temperature limits for bulk fuel transfers.

For most applications, Cloud Point is the most useful property when considering fuels and blend levels for winter. It is more conservative than CFPP and much more common and convenient than LTFT.