How Do Diesel Fuel Filters Work?

by Laura Stuart

Fuel Filters

There are few differences between fuel filters and diesel fuel filters, with shape being the most distinguishable. Fuel filters are usually shaped like a cartridge, while a diesel fuel filter is usually shaped like a bowl so water can be easily removed to avoid contact with moving parts. Fuel moves through the multiple films to clear dirt, particles and other contaminants from the fuel before it goes into the injector and into the engine to avoid damage and clogging.

Diesel Fuel Filters

Diesel fuel filters usually are made in the shape of a basin or bowl. This means the filter curves down. Water collects in the bottom of the bowl, while an open/close valve at the bottom of the bowl allows the water to drain from the basin, leaving only water. It's important to remember the chemistry of an engine. Water has a higher parts-per-liter ratio than diesel does. The differences in density is why the water puddles in the bottom of the bowl and the diesel remains in the basin after the water is drained out. In diesel fuel filters, a heater is built into the structure to remove paraffin, which is caused in low temperatures. Paraffins clog the filter and make the fuel filter obsolete because flow is stopped until the clog is removed.


Maintaining the life and quality of your engine's fuel filter is often as simple as unhooking the filter from the fuel line and replacing it with a new filter. High-end filters can be reusable, but common filters need to be replaced entirely. The function of a fuel filter is to strain out dirt and contaminants from engines. If the straining does not occur, the dirt, grim and contaminants can act as a stopper and significantly reduce the amount of flowing fuel into the engine. Reducing the amount of flowing fuel means the engine's performance is going to decrease until the clog is cleared out of the filter.

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