Cummins N14 STC, Celect, Celect Plus – Service Manual 007-048   Lubricating Oil System Diagnostics

This procedure describes a test for the operation of the lubricating oil systems for the N14 engine model.

NOTE: This procedure requires the use of 15W-40 engine oil and the oil sump temperature to be 79 to 96°C [175 to 205°F].

Install a pressure gauge of known accuracy into the oil rifle to confirm the cab pressure gauge reading. At an oil temperature of 93°C [200°F], the pressure must be as follows:

• Low Idle RPM – Above 70 kPa [10 psi]
• High Idle RPM – 240 to 310 kPa [35 to 45 psi]

If the oil rifle pressure exceeds specifications, check the lubricating oil pressure regulator, signal line, and orifice.

• Inspect the lubricating oil pressure regulator. Refer to Procedure 007-029 in Section 7.
• Check the lubricating oil pump signal tube. Refer to Procedure 007-034 in Section 7.
• Check the lubricating oil pump signal tube orifice. Refer to Procedure 007-049 in Section 7.

NOTE: If the oil rifle pressure is below 70 kPa [10 psi] at 93°C [200°F] maximum and is within specifications at high idle, proceed to check the oil pressure at the end of the piston cooling rifle.

If the oil rifle pressure is below specifications, install a pressure gauge of known accuracy onto the oil cooler filter outlet passage. The filter outlet oil pressure must be as follows:

• Minimum allowable:1200 RPM – 207 kPa [30 psi]
• Rated RPM: 240 to 310 kPa [35 to 45 psi].

NOTE: If the oil filter outlet pressure is within or exceeds specifications at high idle and the main oil rifle pressure is below specifications, proceed to check the oil pressure at the end of the piston cooling rifle.

If the oil filter outlet pressure is below specification at high idle, install a pressure gauge of known accuracy onto the oil cooler filter inlet passage.

At high idle, the filter inlet pressure must not be more than 70 kPa [10 psi] greater than the oil filter outlet pressure.

NOTE: If the oil filter inlet pressure at high idle is more than 70 kPa [10 psi] greater than the oil filter outlet pressure, replace the oil filter and measure the oil filter outlet pressure again.

Install a pressure gauge of known accuracy into the lubricating oil pump outlet. At high idle, the oil pump outlet pressure must be 448 to 586 kPa [65 to 85 psi].

If the oil pump outlet pressure is less than the specification, check for damage to the lubricating oil transfer tube, the lubricating oil pressure regulators, and the lubricating oil pump.

• Check the lubricating oil transfer tube. Refer to Procedure 007-040 in Section 7.
• Check the lubricating oil pressure regulator. Refer to Procedure 007-029 in Section 7.
• Check the lubricating oil pump. Refer to Procedure 007-031 in Section 7.

If oil pump outlet pressure exceeds specifications, change the oil filter and repeat the measurement. If the pressure is still high, check for restrictions in the oil transfer passage, in the oil cooler passages, or in either pump pressure regulator.

1. If at 93°C [200°F] the maximum oil rifle pressure is below 70 kPa [10 psi], or if the oil filter outlet pressure is within or exceeds specifications and oil rifle pressure is below specifications at high idle, install a pressure gauge of known accuracy at the back end of the piston cooling nozzle rifle. At high idle, the oil pressure at the end of the piston cooling rifle must be 240 to 310 kPa [35 to 45 psi].

NOTE: If the piston cooling rifle pressure is within or exceeds specifications and the main oil rifle pressure is below specifications, check for restrictions in the block oil passages or for internal engine damage.

NOTE: If the piston cooling rifle pressure is below specifications and the oil filter outlet pressure is within, or exceeds, specifications, check for broken piston cooling nozzles, missing piston cooling nozzle o-ring, a stuck pressure regulator plunger, or for internal engine damage.