Preparing your truck for winter

Let’s kick this off by saying that not all diesel fuel is the same. While here in Australia, winter conditions are quite mild compared to places like Alaska, home of the Ice Road Truckers, where trucks are expected to operate well below sub-zero temperatures. One of the biggest challenges Ice Road Truckers face is preventing their fuel from freezing.

Surprisingly, in some parts of Australia, trucking operators face similar challenges in severe winter conditions, especially in the high country or inland areas. Where the diesel fuel may get cold enough for the wax it contains to start solidifying, a term sometimes known as frozen fuel.

All diesel fuels contain wax, a natural component of crude oil. One benefit of the wax is that it boosts the ignition quality of the fuel. Nevertheless, suppose the cold weather causes enough wax to solidify (or crystallise). In that case, the fuel lines, filters and strainers in a diesel engine may become blocked and make it difficult or impossible to start and operate the truck. Hence, the phenomenon known as 'waxing' the fuel.

Australian fuel companies make dedicated Winter Diesel blends, specially formulated with lower cloud points than regular diesel, to prevent waxing from happening. The cloud point means the temperature below which wax in diesel will begin to go cloudy and start solidifying.

The Australian Standard for diesel fuel (AS3570-Automotive Diesel Fuel) specifies the cloud point for diesel varies seasonally. Diesel manufacturers produce diesel with a lower cloud point during the winter months. However, this temperature may still not be low enough to prevent waxing from occurring in cold alpine regions.

For example, Caltex Winter Diesel blends not only conform to the specified winter cloud point but are formulated to have even lower cloud points to prevent waxing in frosty or severe winter conditions.

Caltex Highland Diesel has a cloud point of 2°C below regular diesel which is ideal for moderate to cool areas that experience frequent frosts in winter.

Caltex Alpine Diesel has a cloud point of 4°C below regular diesel which is suitable for alpine regions in the north and south west NSW, the Snowy Mountains, northern Victoria and Tasmania.

However, it's worth investigating what happens to fuel at low temperatures to combat cold-related fuel problems better. Firstly, let's clarify some of the terms used when discussing temperature's impact on diesel fuel:

Waxing: As we touched on earlier, when the fuel literally turns to jelly and the wax solidifies is relatively rare. Waxing occurs when the paraffin wax in diesel solidifies because of a reduction in temperature. The fuel temperature generally has to stay below minus -3° Celsius for extended periods of around 48 to 72 hours.

The paraffin wax in diesel solidifies when subjected to extended cold temperatures below freezing, giving the fuel a cloudy appearance. Even so, fuel can begin to cloud at temperatures as high as zero degrees Celsius, but it will continue flowing.

Fuel must remain very cold for long periods before it will actually wax up. It's not uncommon to hear interstate drivers from up north complain about their fuel waxing up when they have to spend a night or two in the southern states during winter. However, that's probably not the actual problem they are experiencing. The more likely situation is ice or solidified paraffin wax in the fuel filter. But more on that later.

Cloud Point: There is a set of sanctioned tests to conclude the cloud point of the temperature a sample of diesel fuel, at which the naturally present paraffin wax in Highland or Alpine diesel fuel begins to crystalise. These tiny particles of floating solidified wax give the fuel a cloudy appearance.

Average cloud point temperatures range from -2°C for Highland diesel to -4°C for Alpine Diesel. On the other hand, summer diesel may be as high as +7°C – but that's dependent on several factors related to the base stock and refining processes used to make diesel fuel.

Pour Point: This is a crucial quality specification for diesel fuels. Specifically, it measures the tendency of a fuel to become more viscous and resist flowing when cold. The pour point is measured slightly above the temperature when a fuel ceases to flow because of the formation of wax crystals that increase its viscosity. Pour point specifications in the Australian Standard are the maximum allowable temperature. But for diesel truck fuel, the lower pour point is more desirable.

Cold Filter Plugging Point: This is a measurement based on a standardised test that indicates the rate of diesel fuel flow through a standardised filtration device for a predetermined length of time when cooled. The point at which the sample fails to go through the filter within the specified time is the CFPP.

While "Waxing up" may be a common phrase, it's probably not the primary reason a truck no longer runs. Instead, the more likely culprit is water, or more fittingly, ice. Frozen water can easily clog fuel lines and fuel filters, which starves the engine of fuel. In addition, water freezes at a much higher temperature than fuel, so if you're experiencing problems at temperatures ranging from 0°C to -6°C, you're more likely to have ice in your fuel lines or fuel filters.

A quick way to diagnose the cause is to remove the filter and then look inside for ice. Frozen wax, on the other hand, is gooey and thick.

Water is nearly always present in diesel fuel to some degree. A substantial quantity can accumulate in diesel storage tanks or truck tanks if it isn't removed periodically. Given that water is heavier than fuel, it settles at the bottom of the fuel tank.

You'd be okay if the water stayed there, even frozen, but it never does. Instead, warm fuel melts the water, which sloshes around in the tank when the truck moves. However, it breaks it up into finer droplets that can freeze as they travel through fuel lines exposed to the cold outside air.

But it's more likely that any exposed 90-degree metal bend in the fuel line is where water droplets gradually collect and slow the flow of fuel, and the water, in turn, freezes, eventually blocking the fuel line. Of course, the same thing can happen with air lines when the air dryer isn't working, but that's another story.

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If any ice crystals make it past a 90-degree bend, the fuel filter filtration media is the next point. In days gone by, tiny ice crystals quickly passed through the media when filter media measured tens of microns. However, with today's 2-micron filters, ice is easily trapped by the filter. If enough ice gathers on the filter media, fuel will no longer flow through the filter, and the engine will stall or not start.

But bear in mind that replacing your fuel filters with a more porous media is certainly not the answer. Modern high-pressure fuel injection systems have very tight internal clearances, and even the slightest debris can cause significant and costly damage. Far more expensive than being held up from the ice in the fuel filter damaging the pump or injectors.

The better solution to lessen your chances of being grounded by humble ice crystals is regularly draining the water out of your fuel tanks. But, of course, that should also include any on site fuel storage tanks.

Finally, our man at Caltex suggests that if you're entering a colder climate this winter, fill up a little closer to your final cold stop over destination to minimise the risk of your fuel waxing up.