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Safeguarding Your Diesel

 Keep your rig on the road with our exclusive guide to avoiding bad fuel.

Fuel is crucial to our overland journeys, but many travellers never put any thought into it beyond having enough, and where to get more. However, diesel fuel is an organic, unstable liquid that can and will go bad. Temperature changes, exposure to water or to the air and other contamination issues can reduce the quality of fuel and have a disastrous effect on your engine. So, let’s take a look at how to avoid disaster.

Water Worries

Water contamination can be the worst threat to a diesel engine, and it’s a shockingly common problem as it’s almost impossible to keep water entirely out of storage tanks at service stations — or out of your vehicle’s fuel tank.

Air inside a partially full tank and fluctuating temperatures lead to condensation within the tank. Underground storage tank contamination can also come from leaks after flooding or heavy rain.

Water mixed into your fuel can decrease fuel efficiency, cause serious damage, increase wear and tear on your engine. But the greatest danger of water in your fuel system doesn’t come from the water itself. Instead, the thing you need to be most concerned about is what’s living in that water.

Diesel Bug Dramas

Water is a breeding ground for bacteria, fungi and algae. ‘Diesel bugs’ is a term for the vast array of these lifeforms that can survive in water within a fuel system. 

Majority of these bugs rely on water to survive and feed off nutrients found in fuel additives. At an extremely fast rate they can multiply, produce waste deposits, die and descent to the bottom of your fuel tank resulting in contaminant build up.  This leads to clogging up of fuel lines, fuel filters, injectors and even the high-pressure pump.

There are a variety of diesel bug additives out there designed to kill the bugs. The problem is, these additives can’t remove the dead bugs themselves, which means the dead carcasses and contaminants can still damage your dual system – especially in common rail diesel engines. It is best to use a diesel bug treatment regularly, to kill any contaminants before they get too advanced.

Common Rail Diesel

A common rail diesel is more prone to fuel issues as it operates with much lower tolerances to deliver fuel to the engine than older direct injection engines. This also means there are additional components involved that are quite fragile. The abrasive nature of rust means even small amounts of it can upset the more delicate internal components in a much shorter timeframe. 

Common rail systems operate at extremely high pressure (up to 45,000psi). A rapid burst of water instead of fuel can damage the injector, in some cases sending debris, like the injectors tip, into the combustion chamber causing irreversible damage to the piston and valves.

When in Doubt, Change it Out!

Regularly replacing your vehicle’s fuel filter is a must. Replace it every time you change your engine oil (10,000km – 15,000km) or before every major trip to avoid issues.  

Keeping a spare fuel filter on board is a smart idea. If you are in the middle of nowhere this could potentially save you waiting days for a replacement filter to arrive.  Make sure you use the highest quality filters available, as many cheaper options will cause more trouble than they’re worth.

Secondary Fuel Filters

For peace of mind and a little extra protection installing a secondary fuel filter is a good investment.  There is some debate whether to fit an extra filter after or pre factory filter. 

Your standard factory fitted fuel filter usually filters down to between 2 and 5 microns, which is designed to suit the rest of your fuel system requirements. Placing an extra fine filter (2 micron) after the factory one can cause problems by affecting the advanced sensors in modern fuel systems. A high-pressure filter usually isn’t very effective against water contamination as the higher pressure forces the water through the filter element.

Instead, a pre-filter (usually around 30 micron) is generally more effective against water, as it gives the water time to hit the filter element and separate. It’s best fitted before the main filter to remove any water before it reaches the finer micron-rated factory unit and limits contamination. 

Reading the Signs

Things like, a loss of power, higher fuel consumption and excessive exhaust smoke are the most common symptoms of a fuel system in distress. There are some more subtle early warning signs that can allude to a problem:

  • Old stale fuel smells off

  • Dark fuel is usually a sign that fuel quality has degraded while hazy fuel indicates water has emulsified in the fuel 

  • Fuel filter blocks up regularly

Top Tips

  • Always avoid filling up shortly after fuel tanks have been topped up at service stations as this disturbs and mixes any water in the tank with fuel – often takes hours to settle back to the bottom.

  • Fill up at frequently used service stations as less risk of water contamination as fuel has been stored in tank for a shorter time. 

  • Steer clear of fuel drums and jerry cans, where possible, as there’s a higher than average chance of contaminants.

  • Fill tank up right before storing your vehicle to reduce oxygen levels required by most diesel bugs to live and lessen condensation.

Who’s Liable?

If you cop a bad tank of fuel, there is a chance the service station will compensate you for any damages incurred, provided there is enough evidence to prove they are at fault.  With that in mind, you should:

  • Always obtain a tax receipt and note the bowser number

  • Try to fill up a full tank at a time as easier to identify service station responsible for any contamination

  • If making a claim, try and track down other motorist that have suffered the same fate as this strengthens you claim


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