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Oil pressure is vital to the engine, which is why there is a warning system on every marine engine that gives an alarm if the oil pressure drops below a certain value. The values vary per type of ship's engine, but they will continue to be between 0.25 and 0.75 bar. The alarm system can be implemented in different ways. With small marine diesel, there is usually only an oil pressure light and a buzzer that will go off when the pressure is too low. The larger ship diesels have an oil pressure gauge in addition to an oil pressure light, a buzzer. The oil pressure must be stated in the engine manual, this will be somewhere between 2 to 4 bar for the average marine diesel. The oil pressure is set by means of an oil pressure valve incorporated in the engine oil lubrication system. If you have an oil pressure gauge and your gauge indicates a pressure of 1 to 1.5 bar, this does not have to be bad if the engine is already 40 years old. Due to the wear of the bearing, the oil pressure becomes lower.
Oil pressure gauge Oil pressure sensor
Diesel engine lubrication schedule.
Oil pressure sensor.
The oil pressure sensor is available in 2 different versions when it comes to connecting to the oil pressure sensor. You have an oil pressure sensor with 1 connection called W connection where only a warning light in combination with a warning light is connected, do you also want to connect an oil pressure gauge or do you have an oil pressure sensor with 2 connections with a W connection and a G connection where the meter to get connected. With both types of sensors, the engine block is the mass.
Oil pressure sensor connections.
Operation of an oil pressure sensor.
Oil pressure sensor cross section.
1 Sealing ring, 2 diaphragm, 3 switch housing, 4 connection point G wire, switch contact, 6 wire of this which also acts as ground.
The drawing of the above image is a standard oil pressure sensor that makes contact when the engine is stopped, when the engine is running and the oil pressure is at pressure the diaphragm (2) will break the contact (5) and the buzzer with oil pressure warning light will go out .
Oil pressure warning light.
The oil pressure warning light illuminates automatically when the ignition is switched on on the ignition switch accessories. In this position, all warning lights will illuminate as a test, if the key is turned the engine will start and the oil pressure light will go out when the oil pressure is sufficient.
Oil pressure warning light.
Measuring is knowing.
Oil pressure too low.
The oil pressure can become lower over the years, this applies especially to older marine engines where wear on the bearings increases the play on the bearings and therefore the pressure drops. A lower oil pressure can also be caused by the membrane of the diesel fuel lift pump being leaking and diesel entering the crankcase of the engine, this will cause the oil to become thinner and the oil alarm will sound. With diesel in the oil, the oil takes on a greyish color and then stinks of diesel. The wrong oil and especially wrong viscosity also cause an oil pressure alarm. In addition to the points already mentioned, an electrical fault can also cause an oil pressure alarm, such as that the wiring is damaged, but an oil pressure sensor can also break, so that it gives a signal while the oil pressure is good. An oil pressure sensor does not break quickly and last a long time, so if you get an oil pressure alarm, turn off the engine as soon as possible.
Oil pressure too high.
An oil pressure that is too high is also not good for a marine engine. If the oil pressure is too high, you will get excessive wear on the plain bearing of the motor. An oil pressure that is too high can be caused by the oil pressure valve being stuck or the wrong oil being used. In practice, an abnormal oil pressure is often the result of a defective oil pressure gauge and / or sensor.
Test the oil pressure sensor with the engine stopped.
The W connection that gives the signal to the warning light and the buzzer can be measured for correct operation by means of a multimeter. When the engine is off there is no oil pressure and the oil pressure sensor will make contact if it is working properly. You can measure whether or not the oil pressure sensor has resistance with a multimeter that is set to ohm. An oil pressure sensor that gives a low resistance with a stationary engine is good, gives the multimeter a 1 or OL (Open Loop) meaning infinite resistance and that means that the oil pressure sensor is broken. This measurement can only be performed when the engine is at a standstill and the oil pressure sensor connections have been removed.
Oil pressure sensor is good. Oil pressure sensor is broken.
Test the oil pressure sensor with the engine running.
It is also possible to measure the oil pressure sensor with the engine running. An infinite resistance will be measured when the oil pressure sensor is working properly because the oil pressure sensor is not making contact, 1 or OL will be shown on the multimeter display. Also in this measurement, the black cable of the multimeter is the mass and is clamped to the engine block and the red cable to the W connection of the oil pressure sensor.
Check oil pressure gauge and warning light with buzzer on dashboard.
The oil pressure warning light and buzzer are fitted as standard on the dashboard of the engine, and if the engine is equipped with a double-acting oil pressure sensor, an oil pressure gauge is also fitted. The warning light and buzzer are easy to test by connecting the W connection wire of the oil pressure sensor to ground, holding the wire against the engine block will give an alarm. Pay attention!! paint from the engine block can have an insulating effect, so that no alarm will sound if the W connection is held against the block.
W connection wire to ground block gives signal.
Oil pressure gauge.
The oil pressure gauge can also be tested by holding the G connection wire against ground, the oil pressure gauge will then turn all the way to one side. If the oil pressure gauge does not respond, then measure whether there is power on the gauge, also measure the negative connection and the transmitter wire.
Oil pressure gauge connection.
When in doubt whether the oil pressure is in order, you can check with a loose oil pressure gauge tester whether the oil pressure of the engine is still within range.
Oil pressure tester universal.
