Do fuel water separator filters work?

Bad Quality Diesel

Contaminated and dirty diesel affects 4WDers all over Australia, costing drivers thousands of dollars in very expensive engine repairs. It doesn’t matter where you fill up your tank next — whether in the middle of the outback or in the city — your next batch of fuel could be contaminated.

This is such a massive issue, so we spoke to diesel filtration experts to ask how water or contamination in your diesel can affect your expensive engine, how to prevent it, and whether you should run a secondary fuel filter in your 4WD before or after your factory filter.

How Bad Fuel Damages Your Common Rail Engine

Common rail diesel engines can generate over 30,000 PSI in fuel pressure, which is their secret to burning fuel better, resulting in greater power and fuel economy. However, the finer tolerances of these engines make them very sensitive to water contamination in diesel.

Water can corrode the inside of your injectors, causing catastrophic damage to your engine and the injectors themselves. This damage affects the spray pattern, causes fuel leakage, loss of pressure, poor-quality fuel delivery, and worse fuel economy. This irreparable damage to your injectors means they must be replaced, which is a service that costs thousands of dollars.

How To Stop the Delivery of Bad Diesel & Fuel

Diesel quality is a common issue faced in Australia, and it is not a case of if you get a bad batch of fuel, but when. So, how do you stop it from ruining your engine?

Shauno uses a pre-filter installed before the factory fuel filter in every one of his 4WDs. This acts as a water separator for your diesel and serves as an extra line of defence, so your fuel is filtered twice before it reaches your engine.

Testing Diesel Pre-Filters

We set up this test to simulate what happens when you put poor-quality diesel through a pre-filter and how these water separation filters can save your engine from damage.

The test setup showed fuel moving from the tank, through the filter, and into the engine. Some filters have an alarm that is triggered when water or contaminants are detected in the filter, letting you know to stop before further damage occurs.

We poured water through this system to see what would happen — keeping in mind that even the smallest amount of water in your diesel engine can cause huge damage to your 4WD’s injectors.

The water was successfully collected by the filter without any being allowed into the test engine, and the filter’s alarm was triggered, letting us know there was a problem in the fuel. This means you would stop driving and dump out the water before any damage was done.

The simple line of defence of installing a pre-filter water separator can save your engine, injectors, and fuel pump from thousands of dollars in damages and repairs.

Why Can’t Factory Fuel Filters Stop Bad Fuel?

Factory fuel filters are designed to catch a certain number of particles over a specific period, which corresponds to your recommended service interval. They are designed to cope with the amount of water allowed according to the Australian standard of 0.02%, which sadly does not always reflect the reality of fuel quality. This is why an additional fuel water filter is needed to protect your investment.

If you fill up a whole tank of poor-quality diesel, you may get much more contamination in one tank than what the factory filter can handle over a single service period.

What Is Best – Secondary Fuel Filter Before or After the Factory Filter?

Factory fuel filters should be trusted to remove contaminated particles, while the extra filter should focus on stopping water from entering your fuel system. Secondary filters should be fitted before the factory fuel filter to target water separation and allow the factory filter to be the last line of defence for contamination filtering.

To properly filter water, the secondary filter must be more open to allow time for the water to separate. Particle separation layers in secondary filters are only an additional function for pre-filters, which is why they are better suited to be fitted before your factory filter, not after.

Why a Primary Fuel Filter Will Help Stop Water Better

When fuel is pushed through the factory filter, it mixes the water and fuel together, making it harder to separate the water if a water separator is fitted after the factory filter. Catching water with a pre/primary filter before the factory filter is easier, as the water has not yet mixed with the diesel as much.

4 Micron Filter VS 30 Micron Filter

Factory filters are 4 Micron, meaning they are very fine to capture smaller particles. Pre-filters are generally around 30 Microns, which are coarser to allow water droplets to grow large enough to be affected by gravity and drain off.

Fuel flows through the 30 Micron pre-filter slowly to capture water and then passes through the 4 Micron factory filter at approximately 56 times faster speeds to capture small, contaminated particles.

How Does Water Separation Work?

Small water droplets collect on the filter surface, grow into bigger and heavier droplets, and then fall to the bottom due to gravity, where they are collected.

How To Tell If You Have Water in Your System?

Some water separators are fitted with a clear plastic bottom, allowing you to see the amount of water captured by the filter. You should check this often and dump out any water found.

Other filters can have alarms that you can wire into the cab of your 4WD. These alarms will sound whenever the filter needs attention.

Our Verdict

Just remember that your very next tank of diesel could be a bad batch that causes expensive damage to your 4WD’s fuel system. This could cost you thousands of dollars during your next trip to the mechanic.

Installing a pre-filter to separate water from contaminated fuel is a cost-effective DIY project that acts as cheap insurance for your pride and joy!