TECH TALK / Post date: 1 August 2012
As natural gas-fueled engines continue to gain popularity in commercial heavy duty vehicles, it has become increasingly important to educate customers on the unique lubrication requirements for those engines. Several of the most popular gas engines, such as the Cummins Westport ISL-G, Detroit Diesel Series 30/50/60G and the Navistar gas engine variants, specify special oils that are not the same as standard diesel engine oils. The two most common specs are Cummins CES 20074 and DD 93K216.
There are several, but we will focus on oxidation resistance and sulfated ash level. Because the incoming fuel is gaseous and mixed very completely with air, combustion temperatures in gas engines can be significantly higher than in conventional diesel counterparts. Higher operating temperatures create the need for very robust oxidation resistance in the oil. Second, there is no liquid fuel to help lubricate the valves, so a small portion of the lubricant is burned to create an ash layer on the valves, which acts as a solid lubricant. Balancing the ash level is key – too little or too much ash will cause valve problems. Too little ash can cause excessive valve/head wear known as recession. More commonly, we see problems with excessive ash levels, due to customers using higher-ash diesel engine oils instead of what is specified by the OEM. Too much ash will deposit on exhaust valves and ultimately lead to valve destruction over time. This process is known as guttering and torching. A torched valve will result in total loss of compression in a cylinder, requiring a head rebuild.
At this time, many dual-fuel engines do not specify lower ash natural gas engine oils. This is a bit of a gray area because a diesel engine oil will create excessive deposits as described previously, but a gas engine oil is not designed to disperse soot very effectively, as pure gas engines don’t generate much if any soot. For these engines, standard diesel engine oils remain suitable for use. As always, customers should be advised to consult the OEM manual for the appropriate lubricant recommendation.
For those customers that require a natural gas engine oil, Castrol markets two high-quality products. Duratec NG is a conventional oil which is formulated to deliver 600-hour drain intervals in refuse and vocational bus service. Duratec ES is a full-synthetic oil designed to deliver extended drain intervals up to 1200 hours in similar service. Both oils carry Cummins CES 20074 approval, and meet the requirements of DD 93K216.