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Poor Quality Propane and Forklifts

Poor Quality Propane and Forklifts

Is the Quality of my propane fuel causing my forklift to run poorly?

There is a perception that propane quality has diminished over the years causing increased issues with the fuel systems of modern forklifts. While there is no evidence that propane suppliers are providing lower quality fuels it is important that we understand and the fuel standards that the industry uses and what the consumer is paying for and receiving.

Propane Grade

There are 3 basic grades of Propane produced in the US, they are;

  1. Commercial Grade
    • Up to 49% propylene and other gases
    • Used for home heating, appliances and commercial heating operations
  2. HD10
    • Minimum 90% propane (LPG)
    • Up to 10% propylene (propylene is used in the manufacture of plastics)
  3. HD5 (Special-Duty Propane)
    • Minimum 90% propane (LPG)
    • Maximum 5% propylene
    • Remaining 5% to consists of other gases, such as iso-butane and methane

Note: The American Society for testing and materials defines commercial propane gas grades with Standard 1835, listed as ASTM D1835. Some distributers use other classifications as marketing tools, but you can be assured that there are only these three grades as of this writing.

All major forklift manufacturers specify HD5 fuel for use in their engines this is because propylene can cause fuel systems and engine components to “gum-up” or stick during operation. There is also some suspicion that it can cause damage to emission components.

The only reason HD10 is sold to the forklift industry is price. It would be wise to ask your supplier for documentation as to what grade of propane (LPG) you are receiving. Don’t settle for less, it will cost you in maintenance and reliability.


Beyond the grade that your propane is produced is the possibility of contaminates that can be introduced in the distribution chain. Most distributers do a good job of filtering their product but not all impurities are filtered out in this process.

So why do we see increased problems with fuel systems in recent years? The EPA standards that have been introduced in the past few decades have created more complex fuel systems that incorporate injectors, sensors, and computer controls that have increased efficiency but also made them more sensitive to these contaminates.

Preventing Breakdowns

What else does the end user do to prevent breakdowns due to fuel related issues?

  • There are particulate filters located in the fuel systems of all major brand forklifts, these should be changed or cleaned on a regular basis.
  • Many fuel systems have a drain located in the vaporizer section of the fuel system that can be used to remove tars and residue that build up.
  • Following the manufacturers maintenance recommendations at proper intervals can have a major affect on the reliability of your forklift.
  • Operating temperature can affect how contaminants “gum-up” components. Make sure that your cooling system is operating at peak efficiency and the
              thermostat is working correctly.


One other area of note are additives that have been introduced to the market that claim to reduce buildup and decrease fuel consumption. I have not seen any research or had any feedback that these products have any measurable effect. Your results may vary.

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