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What Does Fuel Testing Really Tell you

Posted by: Erik Bjornstad

One thing that sets apart a good tank servicing or fuel polishing partner from a no-so-good one is their familiarity with fuel testing.  The better partners in this area should incorporate ASTM testing into their service protocols, because their goal is to make sure their customers (you) know everything they need to know to make the best decision possible. ASTM testing of stored fuel is the best way to assess exactly how good or bad condition the fuel is in. And ASTM testing after servicing is the best way to document for sure how fuel servicing has benefitted you (or not).

What is ASTM?

You’ll hear the name ASTM referenced many times within the industry.  The American Society for Testing Materials is a broad organization that has developed accepted test standards in virtually every area you can think of, not just fuel.  In collaboration with industry leaders, ASTM will develop the testing methods to address a given question. The resulting standard(s) are usually agreed upon by the members of the applicable industry. 

ASTM itself doesn’t have any ability to enforce anything – they just develop the standards and how to measure them. But it is their standards that are referenced and required by outside organizations like the Federal Government. So when the government says that biodiesel fuel has to meet 7 different ASTM standards or it can’t be called biodiesel, now the standards have teeth.fuel testing

What Do These Tests Mean?

The specification of fuels like diesel and biodiesel are defined by the results of numbered ASTM tests. Each of these tests measures an important property of the fuel – a property that’s been defined (by the industry) as relevant to the fuel doing what it needs to do.  You’ll usually hear the standard referenced by a number and a test name.

A good fuel servicing partner may not coordinate all of these tests – they’re not always needed every time. But they should be able to facilitate getting them if needed.

Flash Point (D93) – this test determines at what temperature the fuel vapors will ignite. If the fuel doesn’t meet a minimum flash point, it won’t burn properly in an engine.  If the fuel is contaminated with something (like gasoline contamination of diesel), it will show up in a skewed flash point.

Cloud Point (D5773) – one of the cold weather property tests, this defines the temperature at which the fuel becomes cloudy due to wax crystals dropping out of solution. This is important to know because, for most fuels, there’s about a 10 degree (F) difference between the cloud point and the lower temperature at which the fuel gels up enough to shut the engine down.

Water and Sediment (D2709) – one of the tests specified by governing agencies to be done by mission critical agencies who store emergency fuel.  This test simply measures the water and sediment content of the fuel. If it’s too high, it can damage equipment and causes corrosion of storage systems.

Microbial Contamination – there are several tests, such as microbe count, that can specifically judge the number of microbes per unit of fuel.   A good fuel polisher will use a biocide in their process, so this test should be run on the finished fuel to confirm that the biocide worked as needed.

Cetane Number – stored diesel fuel needed adequate cetane rating in order to run properly in diesel engines.  There is a cetane number test and also a cetane index, which is a calculation based on the distillation value  of the fuel combined with its density or API index (another way to state density).

If you’re storing B99 biodiesel, there are also other tests (acid number, glycerin content, sulfated ash, rancimat) that you or your fuel partner should be running to document that the fuel you’re using and storing is in proper working order.

If your fuel servicing partner isn’t running these tests or can’t help you get them done, you should consider a different partner if possible.

You may be interested in these other posts on Fuel Storage:


The Essential Fuel Tests You Need to Know About

This post was published on June 29, 2016 and was updated on March 1, 2023.

Topics: Fuel and Tank Services, Fuel Testing