There are 2 major engine mods recommended for turbo diesels; oil catch can and secondary diesel filters. Some will argue for a diesel pre-filter and others will argue for a diesel post-filter. We take a quick look at the difference between diesel pre-filters and post-filters. Then; why or when you should install one on your turbo diesel 4WD.

Secondary fuel filters

The purpose of a secondary filter is to remove more contaminates from your fuel system prior to the diesel going through the injectors. Modern common rail injectors have ultra fine tolerances. These can easily be clogged and cost thousands to replace.

You will read tons of articles telling you not to buy a 2005 to 2009 Toyota Hilux because of “known” injector issues. However the reality this was not exclusively a Hilux issue. Toyota Hilux had the largest market share of 4×4 utes during that period of time. Therefore, more vehicles affected by the issue in general. Talk to any mechanic that services multiple makes of utes and they will tell you they have repaired all brands with injector issues.

One of the solutions to the issue was to install a secondary fuel filter. This removes a greater amount of contaminants from the system. It does this by adding a second fuel filter to the system. But removes different sized particles to the factory system.

Another benefit of a secondary diesel filter is it removes the water from the fuel into a visible bowl. This doubles up with the factory filter that also removes water. But the factory filter only has a sensor on the dash and no visible water level.

Why should you install one?

If you have a new turbo diesel that’s serviced regularly and use a reliable fuel station that supplies clean good diesel than you probably don’t need one.

If however you travel heaps and go to remote servos that look dodgy as, then you probably do. Fuel stations with old tanks are of course more likely to have contaminates. Fuel stations using unreliable fuel sources are more likely to have contaminates.

The other scenario is if your using jerrycans. Anyone transporting and using fuel containers are putting themselves at risk. As they increase the chance of introducing contaminates into their diesel. It doesn’t matter how careful you are something can always goes wrong. Dropping the end of the siphoning hose in the dirt. Dirt falling off the lid into the fuel container. Dropping the fuel container cap. The fuel container slips from your hands. Of course there is always that one mate. The guy that has to help but he is nothing but a pain in the neck…

Fuel cans are great and when your travelling that far, you cant avoid them. Should you be scared of them? No way, this is why we have fuel filters and water separators in our vehicles. But this is exactly why you should have a secondary filter for these “just in case” reasons.

Secondary fuel filters are relatively cheap for the protection they provide. If you go out west get one!

Fuel consumption

If your loading up your vehicle or towing your going to use a lot more diesel. Therefore a lot more fuel passes through the filter for the same distance.

With my Hilux I typically get 70% of the distance under full load than I do unloaded. This means that the filter is filtering 50% more diesel than normal. If you did this for 10,000km, you have effectively put your filtration system through 15,000km equivalent of fuel (I’m not going to bore you with the mathematical details). So how do you ensure your filter is still up to the task without having to service it sooner?

Factory diesel filter

On a Toyota Hilux KUN26R (2009-2015) the factory filter is approximately 4-5 microns. Its manufactured by Denso who also make the factory injectors.

One would safely assume that the factory filter would filter the diesel enough for the factory injectors. So there would never to be an issue if regular maintenance is carried out.

Diesel post-filter

The post-filter is a secondary filter that is fitted after the factor filter (between the factory filter and injectors). Post-filters are a finer filter than the factory filter generally 2 micron vs factory 5 micron.

There are videos on YouTube proving that a 2 micron filter can flow more than enough to not disrupt your fuel system. It “proves” this by showing the amount of diesel returning to the tank and the vacuum levels.

I have an issue with these tests, because they are conducted in a “perfect” scenario; clean fuel and new filters. Not with fuel from a contaminated source, which is the whole point of a secondary filtration system.

What happens at 9,000km (after the last service)? After filling up at several dodgy fuel stations under full load (using 50% more fuel), when the filters are close to needing replacement? Could the 2 micron filter could start to clog and not allow enough diesel to pass through the system?

What’s the purpose of filtering to 2 microns if the system can handle up to  5 microns? I feel your unnecessarily putting your fuel system at risk. By refining the fuel to a level beyond necessary.

Using a post-filter as a secondary filter also means the factory filter is doing all the primary water separation. But the factory filter does not have a visible water catch bowl unlike a secondary filter. So you are relying on the vehicle fuel sensors to report the water level to you (after it’s to high).

The factory filter contains sensors that go to the computer and light up the dash. By installing equipment between the factory filter and injectors, there is a chance you can upset the factory settings. This could upset the system warnings  and ruin your engine.

Diesel pre-filter

A diesel pre-filter is a filter that is between your fuel tank and factory fuel filter. Pre-filters are a courser filter than the factory filter. Generally a 30 micron pre-filter vs 5 micron factory filter. It also separates the water from the diesel prior to getting to the factory filter.

The diesel pre-filter removes any large particles before they hit your factory filter. This means your factory filter is only filtering particles between 30 and 5 microns, thus removing a load off the factory filtration system.

When the vehicle is under load or heavy towing and your consuming the 50% extra fuel. By using a secondary diesel pre-filter, this should extend the life span of the factory filter. Especially during these scenarios (you should still replace the filters as per the factory recommendations).

By using a pre-filter as the secondary filter also allows the pre-filter to do the primary water separation. This is great as the diesel pre-filter has a clear bowl. So you can see when water is collected. Then you can empty it as soon as possible, before it causes an issue.

Is a diesel pre-filter a DIY job?

Most definitely, the diesel pre-filter kits from Direction Plus are extremely easy to install. If you can install an oil catch can, you can install the secondary diesel pre-filter. I recently installed under tray tool boxes and this was a much more difficult task.

Check the video below to see how simple the install is:

Diesel pre-filter conclusion

If your taking your vehicle to remote areas with unreliable fuel sources. Maybe your using jerrycans to supplement your fuel requirements. Are you loading your vehicle to maximum GVM or towing, causing an increase in fuel consumption? Then you need a secondary filtration system.

I chose a secondary Direction Plus diesel pre-filter kit because of the below:

• They remove the large contaminates allowing the factory filter to filter finer particles for longer (essentially halving the work of the factory filter).
• Diesel pre-filters do the primary water separation and use a clear bowl for easy identification.
• They are fitted before the ECU sensors, allowing engine warnings to operate as per normal.
• They allow fitting of a secondary battery.

 

Disclaimer:

Although I am affiliated with Direction Plus, my decision to use their products was based on my own independent research. I had committed to purchasing their products before they assisted me with this project.