Fuel Filtration

New fuels and new engines demand a new filter regimen

By Tom Jackson

Going green has its drawbacks. When it comes to cleaning up diesel emissions, the price you pay is reduced fuel quality. If you’re not careful, clogged fuel filters and ruined injectors may result.

How particulate and water are removedHow particulate and water are removed

Fresh from the refinery, diesel fuel is fairly clean and contaminant free. But the removal of sulfur in ultra low sulfur diesel (ULSD) and the increasing use of biodiesel blends has made today’s fuel less stable and more likely to pick up water and form other contaminants.

The biggest culprits when it comes to fuel contamination have changed as well. “The returned fuel filters we get today are usually plugged with organic matter, rather than inorganic – soft sticky contaminant, rather than hard particles,” says Brian Tucker, engine liquid product manager at Donaldson.

What this means is that you need to fundamentally change how you deal with diesel fuel from your bulk storage tanks to your engine fuel filters. To counteract the threat you first need to be aware of the changes in your fuel and engines.


“Biodiesel is an industrial solvent,” says Paul Bandoly, manager of technical services/customer training at Wix Filters. This solvent action presents two problems. Initially, when biodiesel is added to your fuel tanks it will dissolve deposits, by-products of oxidation and other contaminants in your system and throw them at the filter.

“If you have dirty dispensing equipment, dirty storage tanks or dirty-on board vehicle systems, you’re going to run through filters like crazy,” Bandoly says.

The second issue with biodiesel is that it loves water. Water breeds microbes and these microbes feed on the fuel and excrete acidic waste products. Dead microbes and waste equal sludge in the tanks. Even when biocides are added to kill microbial growth, that in itself may shorten filter life as the microorganisms are removed by the filter, says Steve Englund, senior product management administrator with Baldwin Filters. Once the system fuel is free from the microbes and/or the residue of biodiesel’s solvent action, filter life should return to normal, Englund says.

Ultra low sulfur diesel

The sulfur levels on diesel fuel, both on and off highway, have been cut more than 95 percent compared to just a few years ago. This naturally occurring sulfur provided lubricity, but today lubricity additives are needed to prevent injection wear, says Brent Birch, engineering lab manager for Luber-Finer/Champion Laboratories.

“In most cases these additives should be added before the fuel is shipped from the distribution terminals to the end users,” Birch says. Soy based bio-fuels are a good lubricity agent. But additives can affect the water separation capabilities of fuel filters and the additives for petroleum diesel and bio-diesel are not necessarily the same, due to differences in fuel chemistry.

Fuel filter designs are changing to perform as well as possible with the current fuels, says Birch. But he cautions: “It just takes one fill-up of off-spec fuel to plug a filter.”

High pressure injection

To cut exhaust emissions, manufacturers have ramped up injection pressures in new engines to 30,000 psi or more. These high pressure bursts better atomize the fuel and can be combined in up to five separate injection “events” per combustion cycle. This promotes a more thorough and efficient burn of the fuel and less soot and wasted fuel going out the exhaust valves.

In order to deal with these high injection pressures, filter manufacturers have had to create filter media that can trap hard particles as small as 2 microns. Just a few years ago filtration down to 10 microns was considered sufficient. But large particles under high pressure act like abrasives, wearing away injector tips and fuel pumps.

Filtering hard particles to 2 microns has proven relatively easy. New synthetic media and combinations of synthetic and organic media can handle that with no compromise in filter life and performance.

“Many engine manufacturers are charging the secondary fuel filter with pressure to increase injection pressures,” says Mark Stamp, heavy-duty product manager for Luber-Finer/Champion Laboratories. “Increases in the filter shell thickness and gasket component construction are common, which makes it critical to use good quality filters for those applications,” he says.

Tank Cleaning Time“Efficiency and life are usually a tradeoff, so to break that tradeoff you use alternative media, usually multi-layer synthetics that provide higher efficiency,” says Tucker.

Filters not only need to capture smaller particles, but a greater percentage of these particles as well. To attain longer filter service intervals in some applications manufacturers will use larger filters to accommodate more media, says Englund. Others use multiple filters and some multi-stage filters within the same canister.

Emulsified water

Where the big challenge comes in is controlling emulsified water. Since water is heavier than diesel fuel, free water drops to the bottom of the filter where its easily drained off. But emulsified water – microscopic droplets of water that get churned into the fuel – are more difficult to remove.

Ironically, back when injectors ran at 3,500 psi rather than 30,000 psi, the treatment for free water in fuel was to pour in an additive that emulsified the free water so it could slip through the filter media. This is the opposite of what you want to do today. “These emulsifying additives are the stuff that people have been using for years to treat the fuel, especially pour point depressants,” Bandoly says. At 3,500 psi, emulsified water did no appreciable damage to injectors or pumps. But today that would compromise a modern high pressure common rail fuel system.

“It just takes one fill-up of off-spec fuel to plug a filter,”

 – Brent Birch, Luber-finer

Accordingly, you have to be very careful about the additives you use. “If you must use an additive make sure it specifically has the word de-emulsifier on the label or spec sheet,” Bandoly says. A de-emulsifier will help the microscopic water droplets coalesce and drop to the bottom of the filter.

Multi-layer media

Most filters today will use a surface tension or a coalescing filter, or a combination of those two technologies to handle emulsified water. In a multi-layer media the synthetic layers have very fine fibers and a lot of surface area where the water droplets come into contact with the media. These stop the droplets and allow them to grow in size. As they grow they contact the organic cellulose media which has been treated with silicone says Tucker. “It’s hydrophobic, so it repels water and knocks the droplets out of the fuel stream.”


If you’re experiencing fuel filter problems and want to run some quick diagnostic checks, you can put a used filter in a freezer bag and set it in the sun for a few hours, says Paul Bandoly, manager of technical services/customer training at Wix Filters. If you see condensation you have a water contamination problem. You can also cut open a used filter and check for the following:

1. If there is black, tarry stuff it’s usually asphaltines from the fuel breaking down and oxidation.

2. If it’s stinky and slimy and black, rust or olive drab green, that’s usually an indication of microorganism contamination.

3. If the filter looks like the day it was made but appears to be coated with shellac and completely plugged, those are glycerides. Somebody sold you a bad batch of biodiesel.

“In the past the media was not capable of presenting a good barrier to progression for these small, emulsified water droplets,” Bandoly says. “Today the media is much more capable.”


The best way to keep your injectors and pumps in good condition and lighten the load on your fuel filters is to prevent contaminated fuel from reaching them in the first place. “In my opinion you’re not running any greater risk using a proper blend of biodiesel than you are with 100 percent petro-diesel – if your housekeeping and usage are all first rate,” Bandoly says.

Just keep in mind housekeeping is more important than ever. Here are some suggestions:

Biodiesel. Make sure the biodiesel you are using conforms to the ASTM D 6751 and the supplier meets the BQ9000 certification standard. When you do make the switch, clean your tanks with a pump/filtration system like the one shown on the opposite page. This will remove the sludge, sediment and deposits that biodiesel will dissolve in your tanks. Continue to filter bulk fuel until you’re satisfied that the tanks are clean. Then keep them clean with periodic maintenance. You may also have to shorten your fuel filter change interval until the contamination is gone from your tanks.

Fresh fuel. Plan your fuel deliveries to make sure the fuel you have on hand is fresh. About six months is as long as you want to store today’s ULSD or biodiesel.

Spare filters. Store an extra fuel filter on your machines. It’s a lot less expensive and time consuming for an operator to replace a clogged fuel filter than to have a technician come out in a truck and do it.

Top off. Fill up equipment tanks at the end of the day. A half empty tank of warm fuel will condense water vapor overnight. Fill that space with fuel to reduce condensation.

Bulk filtration. If you store the fuel you use, clean your tanks periodically and install bulk filtration and water separation units on the storage tanks.

Breathe clean. Use desiccant breather filters on machines and bulk storage units. A number of breathers offer 2- to 30-micron filtration for hard particle contamination and some kind of water absorbent desiccant to take out moisture that results from humidity in the air, says Mike Gruca, product engineer for Luber-Finer/Champion Laboratories. EW