This week, the need arose to add a little bit of oil to the Cummins ISX12-G that powers my Freightliner Cascadia. I decided to stop on by and grab a gallon of oil from one of only a couple places I know of that carry the oil I need. You see, this is not your average diesel engine oil that I buy. Around my area, only a handful of heavy-duty part stores carry it. In a regular diesel powered truck you can typically walk in to 
the travel center service area and grab a gallon to go if you need to top off the engine oil. Whether you run conventional, synthetic, or even synthetic blend, these days most truck stops have what you need. A CNG engine is different however, with its ability to degrade oil with the accumulation of oxides of nitrogen, called nitration, and special attention needing to be paid to sulfated ash. So for those that think any oil will do for lubricating an engine, be aware of the differences, especially if you drive a CNG powered truck!
Finding the proper engine oil has become easier, but I went on high alert when the store I usually get it at was out. The gentleman at the counter questioned why I couldn't just use regular heavy-duty oil? Thus ensued the “educational workshop” with the service people. They were happy to have learned the difference in the end and I was glad to have opened the eyes of the crew behind the counter, so as to not have them give the wrong oil to another driver that may stop by in the future and be looking for natural gas engine oil. Something tells me that if I had not known myself, they might have just led me over to the shelf for a gallon of synthetic diesel engine oil!
Cummins suggests oil/oil filter change intervals on this particular engine of 25,000 miles/500 hours/6 months (assuming normal duty), which is a pretty reasonable interval when compared to diesel engines. The cost will be a little more than diesel oil, but you can save yourself a bit if you order it in 5-gallon pails instead of single gallon jugs. Learning from this item being out of stock this one time, I am going to buy a 5-gallon pail myself and fill some of my empty gallon jugs to carry onboard.
Remember, any natural gas engine oil you use should be CES 20074-approved. Cummins even warns in their service interval brochure “Do not use diesel engine oil in a natural gas engine. If diesel engine oil is used, valve torching, piston scuffing and reduction in spark-plug life will occur.” Some of the major players in engine oils have released great options for natural gas 
engines now; Valvoline’s Premium Blue GEO Engine Oil, Shell Rotella’s T3 NG, and Chevron Delo’s 400 NG. With more formulations of this special 15W-40 oil from more brands becoming available, it should get easier to find these oils in stock as the amount of natural gas trucks on the road continues to grow.