What is the freezing point of diesel?

Like most fuels, diesel is a mix of hydrocarbons, and the components have different freezing points. For Number 2 diesel, as the ambient temperatures drop toward 0°C (32 F), it begins to cloud, due to the paraffin in the fuel solidifying. As the temperatures drop below 0°C, the molecules combine into solids, large enough to be stopped by the filter. This is known as the gel point, and generally occurs about -9.5 degrees C (15 degrees F ) below the cloud point.

This wax then forms a coating on the filter which results in a loss of engine power. The same thing happens on starting an engine when the temperature is below freezing. The filter becomes almost instantly coated with wax - usually, enough fuel gets through to allow the engine to idle, but not attain operating RPM. There are two common ways to overcome this: one is a diesel additive, the other is a fuel heater.

In Alaska and other colder climates, lorries are running regularly at -46°C (-51 F) or lower, so as you see, it depends on additives and heating. But to freeze - as in turning solid - you would need laboratory conditions; nature cannot go cold enough to freeze to a low enough temperature.

Freezing of Gasoline (Petrol)
Fuels (like gasoline) are really a cocktail of hydrocarbons: thicker, oil-like stuff at room temperature with some thinner ones, and also aromatics that are gaseous at room temperature.

So, by freezing, is the question asking when it turns solid? The heavier hydrocarbons will start to solidify sooner than the aromatics.

The flash point of gasoline is about -72°C (-97F), meaning that it will still burn at 72 degrees below zero. Most labs won't even have the ability to chill a sample down that far to find out! Even the -72°C mark is going to vary, based on the additives in the sample.

Of course, if there is any water mixed in with the fuel, it can still freeze at around 0°C, but that may depend on if there are any alcohols mixed with the sample. Methyl alcohol is a common additive you can buy to help keep water in your gas tank from freezing at low temperatures.

The thicker, heavier hydrocarbons, like paraffin, will become solid at atmospheric temperatures. Some of the aromatics won't turn solid until -100 to -200°C (-200F to -300F). Not something you'll see outside of a lab.