3116 Truck Engine Caterpillar

Measuring Engine Oil Pressure

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Work carefully around an engine that is running. Engine parts that are hot, or parts that are moving, can cause personal injury.

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1U-5470 Engine pressure test group

The 1U-5470 Engine Pressure Test Group measures the oil pressure in the system. This engine tool group can read the oil pressure inside the oil gallery.

Note: Refer to Special Instruction, SEHS8907, "Using the 1U-5470 Engine Pressure Test Group " for more information.

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Oil pressure test location (1) Oil gallery plug

1. Remove oil gallery plug (1) from the side of the cylinder block.

2. Install the following Tools into the port in the left side of the engine: 1U-5470 Engine Pressure Test Group, 8J-7844 Adapter Fitting, 3K-0360 O-Ring Seal and 4M-5317 Reducing Bushing .

3. Start the engine. Run the engine with SAE 10W30 oil. Refer to Operation and Maintenance Manual, "Engine Oil" for the recommendations of engine oil.

4. Record the value of the engine oil pressure when the engine is at operating temperature and operating under full load.

   The minimum engine oil pressure should be approximately 250 kPa (36 psi). Minimum engine oil pressure at low idle rpm (750 to 850 rpm) should be approximately 100 kPa (15 psi). Maximum engine oil pressure should be approximately 600 kPa (88 psi) when the engine is at operating temperature and operating under full load condition.

5. Compare the recorded engine oil pressure with the oil pressure indicators on the instrument panel.

6. An engine oil pressure indicator that has a defect or an engine oil pressure sensor that has a defect can give a false indication of a low oil pressure or a high oil pressure. If there is a notable difference between the engine oil pressure readings make necessary repairs.

7. If you have determined that the engine oil pressure is low, then go to "Reasons For Low Engine Oil Pressure".

8. If you have determined that the engine oil pressure is high, refer to "Reason for High Engine Oil Pressure".

Reasons For Low Engine Oil Pressure

Engine Oil Level Is Low

Check the engine oil level in the crankcase. The oil level can possibly be too far below the oil pump supply tube. This will cause the oil pump not to have the ability to supply enough lubrication to the engine components. If the engine oil level is low add engine oil in order to obtain the correct engine oil level. Refer to Operation and Maintenance Manual, "Engine Oil" for the recommendations of engine oil.

The Engine Oil Pump Is Faulty

Check the following problems that may occur to the engine oil pump.

1. Air leakage in the supply side of the oil pump will also cause cavitation and loss of oil pressure. Check the supply side of the oil pump and make necessary repairs. For information on the repair of the engine oil pump, refer to Disassembly and Assembly, "Engine Oil Pump - Remove".

2. Oil pump gears that have too much wear will cause a reduction in oil pressure. Repair the engine oil pump. For information on the repair of the engine oil pump, refer to Disassembly and Assembly, "Engine Oil Pump - Remove".

The Oil Pickup Tube Has A Leak Or A Restricted Inlet Screen

The inlet screen of the oil pickup tube for the engine oil pump can have a restriction. This restriction will cause cavitation and a loss of engine oil pressure. Check the inlet screen on the oil pickup tube and remove any material that may be restricting engine oil flow. Low engine oil pressure may also be the result of the oil pickup tube that is drawing in air. Check the joints of the oil pickup tube for cracks or a damaged O-ring seal. Remove the engine oil pan in order to gain access to the oil pickup tube and the oil screen. Refer to Disassembly and Assembly, "Engine Oil Pan - Remove and Install" for more information.

Engine Oil Is Contaminated

Engine oil that is contaminated with fuel or coolant will cause low engine oil pressure. High engine oil level in the crankcase can be an indication of contamination. Determine the reason for contamination of the engine oil and make the necessary repairs. Replace the engine oil with the approved grade of engine oil. Refer to Operation and Maintenance Manual, "Engine Oil" for the recommendations of engine oil.

The Engine Oil Bypass Valves Are Open

If the engine oil bypass valves are held in the open position, a reduction in the oil pressure can be the result. This may be due to debris in the engine oil. If the engine oil bypass valves are stuck in the open position, remove each engine oil bypass valve and clean each bypass valve in order to correct this problem. You must also clean each bypass valve bore. Install new engine oil filters. New engine oil filters will prevent more debris from causing this problem. For information on the repair of the engine oil bypass valves, refer to Disassembly and Assembly, "Engine Oil Filter Base - Disassemble".

The Engine Lubrication System Is Open

An oil line or an oil passage that is open, broken, or disconnected will cause low engine oil pressure. An open lubrication system could be caused by a piston cooling jet that is missing or damaged. Determine the reason for an open lubrication system of the engine and make the necessary repairs.

Piston Cooling Jets

The piston cooling jets direct engine oil toward the bottom of the piston in order to cool the piston. This also provides lubrication for the piston pin. Breakage, a restriction or incorrect installation of the piston cooling jets will cause seizure of the piston.

Engine Bearings Have Excessive Clearance

Excessive clearance at engine bearings will cause low engine oil pressure. Check the engine components that have excessive bearing clearance and make the necessary repairs.

Reason for High Engine Oil Pressure

Engine oil pressure will be high if the engine oil bypass valves become stuck in the closed position and the engine oil flow is restricted. Foreign matter in the engine oil system could be the cause for the restriction of the oil flow and the movement of the engine oil bypass valves. If the engine oil bypass valves are stuck in the closed position, remove each bypass valve and clean each bypass valve in order to correct this problem. You must also clean each bypass valve bore. Install new engine oil filters. New engine oil filters will prevent more debris from causing this problem. For information on the repair of the engine oil filter bypass valve, refer to Disassembly and Assembly, "Engine Oil Filter Base - Disassemble".