Owning and operating a compressed natural gas-fueled car is an experience closer to having a traditional internal combustion engine vehicle than electric vehicles are to ICEs. Maintaining an EV is mostly about testing battery systems, electric motors and the regenerative brakes. Maintaining a CNG vehicle is more like what most drivers are used to, except for the huge storage tanks in the natural gas vehicle. Regular oil changes are needed in CNG vehicles, but they do differ from gasoline and diesel engine vehicles?

While Automotive Service Excellence (ASE) hasn't published test results yet, the question of engine oil life does tend to come up for those talking about CNG-powered vehicles. Some mechanics pull out the dipstick and take a look at the oil's color. Is the appearance of the dipstick a reliable indicator in CNG vehilces?

Dave Crowley, an instructor at Natural Gas Vehicle Institute, says that you can't rely on the visual appearance – it may look clean, but could be long overdue for a change. While the base oil doesn't wear out, it changes chemically over time, and critical additives are depleted. A few of the changes Crowley looks for:
  • Viscosity: Using CNG eliminates fuel dilution of oil and it thickens over time, which can have a negative effect on a lubricant's ability to protect the CNG engine.
  • Oxidation: CNG engines go to higher temperatures than gasoline and diesel engines in the combustion chamber and upper cylinder, increasing the rate of oxidation.
  • pH Balance: Formation of acids is normal in ICEs, and some natural gas can bring additional acidity. Natural gas composition can vary by region and source, making it necessary to do oil analysis to get an accurate reading of the CNG-powered vehicle's oil quality.
CNG motor oil usage is not as visibly noticeable as ICE lubricant due to the lack of carbon in CNG. Fleet operators can collect oil samples and send them out for lab analysis. Of course, it makes sense to follow the vehicle manufacturer's suggested oil changes, just as you would with ICEs.

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