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Lubricants formulated for use in natural gas fueled engines must provide adequate engine lubrication, minimal thermal degradation, and good deposit control. No API category currently exists for natural gas engine oils. Therefore, selection of the proper engine oil is limited to the two lubricants listed in Table . These oils have demonstrated adequate performance in these engines.

Viscosity Grade, SAE


Sulfated Ash Content, % max. ‪

0.50% ‪

Phosphorous, ppm max. ‪

800 ppm max. ‪

Series 50G Engine Lubricating Oil Specifications

While Detroit Diesel does not maintain an approved list for these lubricants, other lubricants may be selected by the customer provided the oil supplier can demonstrate equivalent performance with the two oils identified. Detroit Diesel will not determine this equivalency.

Oil Change Intervals for Series 50G Engine

During engine operation, lubricating oil deteriorates due to combustion by-products and contamination. Oil change intervals may vary depending on engine operation, fuel quality, and lubricant quality. The oil drain intervals are listed in Table and listed in Table . ‪


Oil Drain Interval*

City Transit Coach ‪

6,000 miles (9,600 km) or 3 months* ‪

Pick-up and Delivery Stop and Go ‪

6,000 miles (9,600 km) or 3 months* ‪

Maximum Recommended Oil Drain Intervals (Normal Operation) for Series 50G Engine


Oil Drain Interval*

Standby Set Full Time ‪

250 hours or 12 month* 250 hours or 3 months* ‪

Stand-by Continuous/Prime ‪

200 hours or 6 months* 200 hours or 3 months* ‪

Stand-by Continuous/Prime ‪

150 hours or 3 months* 150 hours or 3 months* ‪

Maximum Recommended Oil Drain Intervals for Series 50G Generator Set Engine

Note: Fuel with total sulfur greater than 17 ppm, but less than 24 ppm.

Note: Fuel with total sulfur greater than 24 ppm, but less than 32 ppm.

Note: * Whichever comes first.

Used Lubricating Oil Analysis for the Series 50G Engine

A used lubricating oil analysis, such as Detroit Diesel's "Power Trac," is recommended for monitoring crankcase oil in all engines. The application of used engine oil analysis to natural gas fueled engines can help to identify contamination from excessive wear metals and foreign substances and monitor oil degradation through oxidation. If any abnormal conditions are identified, the oil should be changed immediately. Warning limits are listed in Table . ‪

Viscosity Increase, % from new, max. (ASTM D 445) Kinematic @ 100_C ‪

10% ‪

Total Base Number decrease, max. (ASTD D 4739) ‪

3 ‪

Total Acid Number increase, max. (ASTM D 664) ‪

2 ‪

Iron Content, ppm ‪

150 max. ‪

Oxidation/Nitration, Infrared Spectroscopy ‪

25 absorbency units ‪

Used Oil Analysis Warning Limits for Series 50G Engine