LINK AS 5129015 - Caterpillar

Low Oil Pressure
The following conditions will cause low oil pressure.
The oil level is low in the crankcase.
A restriction exists on the oil suction screen.
Connections in the oil lines are leaking.
The connecting rod or the main bearings are worn.
The rotors in the oil pump are worn.
The oil pressure relief valve is operating incorrectly.
Incorrect grade of oil for the relevant ambient temperature.A worn oil pressure relief valve can allow oil to leak through the valve which lowers the oil pressure.The minimum oil pressure at a minimum engine speed of 1200 rpm and at normal operating temperature is 315 kPa (45 psi). A lower pressure is normal at low idle.A suitable pressure gauge can be used in order to test the pressure of the lubrication system.High Oil Pressure
High oil pressure can be caused by the following conditions.
The oil pressure relief valve is operating incorrectly.
Incorrect grade of oil for the relevant ambient temperature.
Excessive sludge exists in the oil which makes the viscosity of the oil too high.