Measuring Cooling Water Pressure

Optimizing the performance of Boston Whaler boats
jimh
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Measuring Cooling Water Pressure

Postby jimh » Tue Jun 21, 2022 9:56 am

Often modern outboard engines are being mounted at a raised engine mounting height compared to the traditional lowest-possible mounting height. As the engine mounting height is raised, the engine cooling water pressure may decrease. Being able to monitor the engine water cooling pressure will give insight into how raising the engine mounting height will affect engine cooling.

By monitoring the cooling water pressure, an inference can be made about the condition of the water pump and cooling system function. Decrease in engine A sudden loss of water pressure can be a sign of impending engine overheating.

There are three general types of engine cooling water pressure gauges: hydraulic, electric, and digital.

Installation of a cooling water pressure gauge is very simple if the gauge is an older hydraulic-type that just connects via a small hose to a hose barb that is threaded into a boss on the engine block designed as the tap-off spot by the engine manufacturer for monitoring water pressure.

Electrical monitoring of engine cooling water pressure is usually accomplished by installing a pressure transducer at the monitoring point. The pressure transducer typically provides a resistance that varies with water pressure. An electrical gauge can be connected to the transducer for monitoring the water pressure. This method avoids having to run a long hose between helm and engine. Usually just one wire is needed, as the engine chassis provides the other half of the circuit.

Digital monitoring of engine cooling water pressure is usually done with NMEA-2000 protocols, In very modern and sophisticated engines, the engine control unit may have been pre-configured with wiring to connect to a pressure transducer, and the resistance of the transducer is then converted into pressure value by an algorithm in the control unit. That data is then sent using NMEA-2000 network protocol to a network bus, where other devices can receive the data and display it in some manner.

In the NMEA-2000 protocol there is a data set or "parameter group" designated as parameter group number 127489, Engine Parameters, Dynamic. In PGN 127489, there is a reserved FIELD in the data for ENGINE COOLANT PRESSURE. This field allocates a 16-bit integer to indicate the engine coolant pressure in units of 100's of Pascals. One Pascal is equal to 1-Newton-per-Meter-squared. At the display device, the value in Pascals is usually converted into PSI. The relationship between Pascal and PSI is

    1-PSI = 6,895 Pascal

This gives a reading of water pressure with a resolution of better than 0.1-PSI.