• Sep 4, 2012
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.


I'm reporting this comment as:

Reported comments and users are reviewed by Autoblog staff 24 hours a day, seven days a week to determine whether they violate Community Guideline. Accounts are penalized for Community Guidelines violations and serious or repeated violations can lead to account termination.


    • 1 Second Ago
  • 9 Comments
      TPGIII
      • 1 Hour Ago
      Interesting. I didn't realize how bad oil can be and still look clean. My hybrid recommends oil changes every 10,000 miles, but I've noticed that the oil, a 0-20W, still looks cleaner after 10,000 miles than many oils look in new condition. I had thought about extending the time between changes since the warranty has now ended, but this is more information to think about. I once had a Ford that recommended changes every 5,000 miles, but after 180,000 miles I figured that going 10,000 miles couldn't hurt. I put 260,000 miles on the car and still never had any problem with the engine, it was still the solidest part of the car.
        bcsaxman
        • 1 Hour Ago
        @TPGIII
        Your oil looks so good because a hybrid car's ICE doesn't run as long or as often in the same 10k mile period as a regular car's ICE does. In other words, a normal car's engine is running for the full 10k miles, while a hybrid car's engine turns on & off intermittently during the same 10k miles, only being used when the batteries can't handle the load any longer, which means it isn't running nearly as much - maybe only 5-7.5k miles of actual ICE use is occurring when driving 10k miles in a hybrid. Plus, typically hybrids use battery power the majority of the time during stop & go driving. Stop & Go driving is the hardest type for an ICE to deal with, and thus the hardest on the oil in the ICE. A hybrid's ICE hardly ever gets exposed to that type of driving, so it's oil will be in better shape over any given distance driven under those conditions. What it all means is that an ICE in a hybrid can expect it's oil to last quite a bit longer than one in normal car. I would estimate a minimum 30-40% increase in the normal 10k oil change interval with typical use. Why the manufacturers are still recommending the same intervals as their normal cars prbably has more to do with being on the safe side with a relatively new technology ... plus, keeping their dealers and oil company shareholders happy should not be discounted as factors too.
      Dave
      • 1 Hour Ago
      I just wanna know where I can buy a CNG powered Miata. (that is a Miata in the pic)
        EZEE
        • 1 Hour Ago
        @Dave
        I like the sawed off soda bottle funnel...
      Smoking_dude
      • 1 Hour Ago
      Viscosity: The problem is not the thickening of the oil, it is the unburned fuel. Gasoline is not good for lubrification as it slowly replaces the oil. A car used in city traffic mostly has "thin oil", driving now at high highway or even autobahn speeds hurts the engine. It takes some time for the gas to evapourate, but in the meantime there is a measurable damage. (Germanys ADAC (AAA) tested it) with CNG or LPG there is no problem like that. so it is a good thing. no soot: the oil stays clear, it has to "carry" less soot and dirt, so it lasts longer. I often skip one change because the oil looks like new. Never harmed the enigne. Oxidation: use a good synthetic oil. cars with (oil lubricated) turbo chargers have a higher thermal on the oil stress too, yet there is no whining about that. just use a good oil.(gets some bonus mpgs too) pH Balance: even with acids, at least in europe CNG/LPG are very clean. no comparison to gas. even on modern cars with catalytic converter. the gasoline smells especially at cold start(catalytic converter to cold). (petrol heads like it, i don't, (still car enthusiast)) but a cold start on lpg/cng and the stench is gone. big difference.
      lad
      • 1 Hour Ago
      Went down to the auto store to buy oil the other day...dyno oil was $4 a qt. Looks like we are being had from the tank to the crank case by Big Oil. Time to think about the true cost of owning and driving IC cars.
        2 Wheeled Menace
        • 1 Hour Ago
        @lad
        Oh yeah. I remember when oil was about 1.50 a quart. And i've only been driving for 8 years or so. Now, recycled stuff is becoming common. But it can't be all that good - how do you restore a lubricant that's broken down? Gas engines are a pain in the butt.
          EZEE
          • 1 Hour Ago
          @2 Wheeled Menace
          2Wheel is against recycling! Get him!
          Greg
          • 1 Hour Ago
          @2 Wheeled Menace
          "how do you restore a lubricant that's broken down?" You put it back in. Recycling is a lot like making it new, except the feedstock is used oil rather than crude. They follow the same process of adding the right chemicals to give it the proper behavior.