Diesel Filtration

Diesel Filtration


Clean, dry Diesel is the key to maximum life from your diesel pump and injectors


Clean, water-free diesel fuel is the single most important thing when it comes to getting maximum service life from your diesel engines injection pump and injectors. Debris and water will very quickly cause wear in the injectors and the suction control valve. The suction control valve is what governs the fuel rail pressure, with rail pressures exceeding 30 000psi (that’s not a typo) and working tolerance of as little as 1 micron it extremely important to supply the injection system with the cleanest fuel possible.

Most OEM (factory fitted) diesel filters have a rating of about %99@10 microns, some a little more, some a little less.
What that means is the filter will trap 99 out of 100 particles 10 microns or larger. The smaller the particle size gets, the efficiency of the filter gets worse.

McGrath Automotive uses Donaldson diesel filters. All of the micron ratings and efficiency’s are available on Donaldson’s web site, enter the part numbers and hit ‘find’. As an example, the part number for a 3.2L Triton has a rating of %99@10 microns at 8 microns it is %95 efficient.
Efficiency at 2 or 3 microns will be close to %50. That is %50 of particles that size will pass through the filter. You may be thinking that an OEM filter is a better option, remember though, that Donaldson filters meet or exceed the OEM spec and Donaldson themselves are suppliers to many OEM truck manufacturers.

So where does that leave those of us who want to protect our expensive diesel injection systems? There is only one solution. We must fit a secondary diesel filter with high efficiency at a small micron. Thankfully Donaldson have filter kits that fit our needs perfectly.
A cost-effective filter with a rating of %99@3 microns and a %95 efficiency at removing water. With this filter installed between the OEM filter and the injection pump, you can be confident you are giving your diesel injection system clean, dry diesel, maximising their service life.


 See our Donaldson filters section here

 Harmful Contaminants Found In Fuel Systems PDF

The Effect of Hard Particle Wear on Diesel Injectors PDF



Diesel filtration misinformation



It has become apparent through our searches for improved products and services that there is much misinformation being spread about diesel filtration. What worse is, it’s coming from places and people who really should know better.

Proper filtration of diesel fuel is the key to a long service life of diesel injectors, and pumps, any business telling you that extra filtration and water separators are needed are in fact correct, and by fitting these products to your vehicle, you are doing the right thing.

The problems start when businesses recommend or sell you the wrong product through their lack of knowledge on how filters work and how filters are rated. I have found many businesses claiming that all common rail diesel engines use 2micron filters, or that a filter traps %100 of particles larger than its micron rating. I’ve even found claims like “all late model diesel engine use 2micron filters”.

Unfortunately, this sort of misinformation leads to people wasting money on products that either do nothing at all to improve the filtration in their fuel systems or only part of what is claimed.

Firstly we need to address how filters are rated.
A micron rating without an efficiency is meaningless information and tells you nothing. Straining your diesel through an old pair of your underwear is going to filter some 2-micron particles. But you are not going to call your old undies a 2-micron filter and trust your engine to them, are you?
You will find efficiency ratings expressed as either a % or a Beta ratio. A beta ratio of B100 is the same as saying %99 efficient. A %99 efficiency (B100) means 99 out of 100 particles at the rated micron size will be trapped by the filter. (or 1 in every 100 will get through)
You may find some filters where multiple efficiencies are listed, Eg: %50@2 micron – %75@12 micron and %99@25 Micron.
Filters are tested using ISO clean fuel and test dust that is of known size and amount. The fuel and test dust is passed through the filter, and the dust that passes through the filter is measured and counted, and the efficiency of the filter is determined.
By know, you should see that there will always be some dust/debris particles that will pass through the filters fitted to your vehicle.

beta ratio

Going back to the statement made by some diesel specialist workshops that, “all modern diesel engines use 2-micron filters”. They have not quantified their statement with an efficiency. Their statement is meaningless and only serves to sell their product.

It is far more correct to say that all modern diesel engine SHOULD be using 2-micron filters with a Beta ratio of 100. The problem is vehicle manufacturers don’t make the information about their filters available to us in the first place. The proof that the factory filters and service intervals are substandard is in the number and types of injector failures the industry is seeing. These failures can only be caused by dust damaging the valving in the diesel injectors.

The next problem we have is the rate of fuel flow through the filter will change the efficiency of the filter. The higher the rate of flow through a given size filter, the lower the efficiency is going to be.
A filter that is suitable for a Hilux is not going to be ideal for a V8 diesel Land Cruiser. Although there are plenty of businesses willing to sell the same small filter kits as suitable for all diesel vehicles.

So far we have established that we can’t quantify the manufacturers’ filters without paying for costly Lab testing, but we can say they are substandard due the number and type of injector failures we are seeing.
Micron ratings without an efficiency are meaningless.
The size of the filter is critical and must be suitable for the flow rate of the fuel system.

So how does this all work in the real world as we are driving our cars? What happens when we fit a 30micron %99 efficient filter before our original filter?
The pre-filter will trap %99 of particles at or above its rating, as the particles get smaller, more and more of the particles will pass through the pre-filter. It is then up to the original filter to finish the job. If %90 of the 2-3-4-5micron particles passed through the pre-filter and we the give the original filter a theoretical efficiency of %65@3 microns %31 of the initial 3-micron particle load will be passing through and on to your injection pump and injectors. The truth is some filters will not even be as efficient as %65.

We also need to remember that laboratory testing also shows us that filter efficiency in an operating fuel system is variable and no filter will always work at its rated efficiency. Efficiency will fluctuate constantly and will improve with dust loading of the filter. This will also be accompanied by increased restriction to flow.

We are left with some questions, What do we do? What do we spend our money on? What if we’ve purchased the wrong thing?

I can answer these questions. Firstly don’t spend your money with any business who merely has filter kits for sale, or who makes filter rating claims without an efficiency.
Buy from a business that takes the time to learn about the products they sell and who can demonstrate an understanding of the operation of the filters and fuel systems.

You should buy a product with micron/efficiency rating that will provide you with a reasonable amount of extra filtration. This means 10-15 micronB100 pre-filters or 2-3 micron B100 final filters.
These filters need to be of adequate size to slow the fuel flow down in the filter and to have a reasonable life.

If you have purchased a 30micron pre-filter, chances are we can supply you with replacement filter of the correct size and micron rating.