Diesel Fuel Gelling

Cold weather can create serious challenges for diesel powered equipment and operations.  One of the most common and costly issues is diesel fuel gelling.  Understanding how diesel behaves in cold temperatures and how to prepare for winter conditions can help prevent downtime, equipment damage, and unexpected disruptions.

What happens to diesel in cold weather?

Diesel contains natural paraffin wax that provides lubricity and energy content.  In warm weather, these stay fully dissolved.  But as temperatures drop, these waxes start to solidify and form crystals.

As these crystals grow, they can restrict fuel flow, clog filters, and ultimately prevent engines from running properly.  This process happens in stages, each marked by a specific temperature range.

Cloud Point – The First Warning Sign

The temperature at which wax crystals begin to form in diesel fuel.  This typically occurs around 14°F.

At this stage:

• Fuel may appear cloudy or hazy
• Wax crystals are present but still small
• Equipment will usually operate normally

Cold Filter Plugging (CFPP)

The cold filter plugging point (CFPP) occurs when wax crystals become large enough to accumulate in fuel filters.  This typically happens between 10°F-14°F.

During this stage:

• Fuel may still appear liquid
• Wax restricts fuel flow through filters
• Engines may experience power loss, stalling, or failure

This is the point where diesel is commonly described as “gelling” even though it may not be fully solid.

Pour Point – When Diesel Fully Gells

The pour point is the lowest temperature at which diesel fuel will continue to flow.  Below this temperature, fuel becomes too thick or solid to move through its system.

Fully gelled diesel typically occurs below 10°F.  If the fuel issues occur between 10°F and 15°F, the cause is usually ice or water contamination, not gelling.  Condensation inside the tank can freeze and restrict fuel flow even when the fuel itself has not fully gelled.