Diesel Fuel Analysis

Terra Analytical can test diesel fuel and similar fuels such as Jet A1 or boiler fuels.  Due to dangerous goods legislation these sample must be sent to the lab via an approved dangerous goods courier.  The diesel test kits contain the appropriate containers, labeling, documentation and courier pack. 

Dangerous goods such as fuel must not be sent via NZ Post in the standard oil test kit mailing containers - please order a Diesel test kit for fuels.  

Terra Analytical cannot test petrol.  There is very strict legislation surrounding the transportation of dangerous goods with a low flash point such as petrol.  We recommend that you contact your petrol supplier/oil company if you have concerns about petrol quality as they have access to test certificates and, if necessary, the appropriate test facilities.

Diesel Contamination

Water Contamination

The most common source of diesel fuel contamination is water. Typically this is condensation from the air volume in the tank. For every litre of fuel used a litre of air must enter the tank to replace this. Air contains water - as much as 17 mL in 1000L. Water can condense on cool surfaces such as the walls of tanks and over time a layer of water will accumulate. The best way to reduce water accumulation is to keep the tank as full as possible by filling it up each night. This applies to all tanks in the chain, including the running tanks of vehicles. A routine maintenance plan to remove water should be put in place. Unfortunately, many fuel tanks don't have a drain point at the lowest point so this not be so easy. Most large commercial fuel tanks will have a water layer that is routinely pumped out by fuel contractors. The pumps can't reach the very bottom so this water layer is maintained within controlled limits. We advise that you should not purchase fuel from a commercial site if you can see a fuel tanker on the site as there is a high chance you might get a little more water than expected. The NZ Government Fuel Specifications allow 200 mg/kg of water maximum for retail sale. Oil and water naturally separate and water has a higher density than oil, so water tends to gravitate to the bottom of any system. It can be possible to operate for years with a tank that contains a lot of water at the bottom, and problems may only be found when the tank is run abnormally low. At that point, the source of the water is highly debatable. It could be from condensation, or there could be holes in the tank, or rainwater might be getting in via a fill point or breather. We strongly recommend that any tank in your care be monitored with water-finding paste on the dipstick. This will tell you how high the water layer is in the tank. For example - it is possible to have a tank with 50% water content - but this would be sitting on the bottom. It would be possible to take a sample of fuel from the top of that tank and it could be tested and the water content could be found to be below 100 mg/kg. Water can be very damaging to engines - water can pass through most fuel filters and cause severe damage to injectors. Some fuel filters may eventually block up with water, but possibly not soon enough to prevent damage. Some filters are better than others, but water is a serious hazard in a fuel system.

Biological Contamination

Along with air entering a tank through the breather, there are millions of airborne contaminants including many microbiological lifeforms. Algae, Bacteria, Fungi, Mold, Yeast etc. Given a water layer, a food source (the fuel or material in the fuel such as sulphur) and the right temperature conditions, these organisms can start to multiply. This may become visible as organic-looking material, from black slime to white fuzz and many other forms. This is a common occurrence - especially in marine environments or warm humid areas. The problem tends to be called 'diesel bug' and there are many additives and treatments on the market for this. There are some myths and misunderstandings about this. The high temperatures used to distil and crack fuel means that there is no significant water or bug in the diesel fuel produced at the refineries. But all tanks in the shipping and distribution chain could possibly be contaminated with water and bugs of all types. Some literature focuses on Cladosporium Resinae as being a common diesel bug that tends to block filters. Our position is that any form of biological growth is a problem - but that water itself is a bigger problem. Bug is often the result of a water layer, and the bug can block filters. But the best course of action is to prevent or remove the water layer first. Identification of the specific bugs is not so important, as the recommended course of action is the same regardless. Terra Analytical uses a 7-day incubation program using agar strips. One side of the agar strip is dosed with a bacteriocide which reduces bacteria growth and allows the slower-growing lifeforms to be visible. This method allows us to give a positive Yes/No recommendation for treating the fuel with microbiocide or not. Although there are many 'diesel bug' additives on the market, we do not recommend dosing a fuel tank before removing the water layer. If a water layer is made toxic, it becomes an environmental hazard when it eventually needs to be removed. It also becomes a health hazard to the fuel contractor. We recommend removing water will it is still just stagnant water. For this reason (and because we take 7 days in a temperature-controlled incubator to check for any growth) we release our fuel reports in two stages. If we find water you will know in the first report - which gives you time to remove the water from the tank. If growth is found after 7 days we recommend treating it with microbiocide (aka 'diesel bug additive') but only if there is something there to kill. Water is the main problem. But we also check a range of tests - elemental analysis can identify the sulphur content and possible contamination. Viscosity and flashpoints can alert to contamination with other fuels such as petrol or oil.

Order a Test Kit today

Terra Analytical lab uses a prepaid test kit system which means we can start testing as soon as we receive your samples. The initial cost of the test kit covers the sample bottle and label, outer mailing canister, testing and reporting of the results.

Most sample tests are covered by a standard oil test kit which can also be used for coolant (not fuel).

We have a range of specialty test kits for specific applications. Additional tests and urgent options are available for an additional fee if necessary. Please contact the lab to discuss options.

Test kits are available over the parts counter from Terra Cat branches throughout New Zealand.