About Bronze Engine Cooling Pumps

Manual Temperature Control
In the discharge line from the raw water pump, fit a branch, controlled by a hand valve, to allow some of the cooling water to by-pass the engine. Start the engine with the by-pass valve open, then close it gradually as the engine warms up, until the optimum temperature is maintained.

IMPORTANT
Do not regulate the pump flow by recycling water from the pump discharge back into the inlet line, or by restricting either the pump discharge or suction pipes.

Automatic Temperature Control
Fit a marine thermostat in the discharge line from the cylinder block. When the engine is cold, the thermostat restricts the flow of cooling water through the engine, diverting most of it to the exhaust via a spring-loaded valve. As the engine temperature increases, the thermostat automatically increases the flow of cooling water through the engine, diverting less through the valve, until the required operating temperature is maintained.

Indirect Cooling via a Heat Exchanger
A pump recirculates fresh water in a closed circuit (the Primary Cooling Circuit) through the cylinder block via a thermostat and a heat exchanger. A second pump delivers river water or seawater ('raw water') to the heat exchanger, maintaining the water in the primary circuit at about 80-90ºC.

Keel Cooling
Keel cooling is a form of indirect cooling with part of the closed primary cooling circuit in the form of pipes, or sometimes a double skin, in the boat's bottom. The heat generated by the engine is dissipated directly to the river water or sea water flowing around the hull. Manual or automatic temperature control is achieved with a suitable by-pass and valve. In principle a single pump can recirculate the coolant, though in practice an additional pump is often required to maintain an adequate flow rate against the extra resistance of the extended pipework.

Raw Water Cooling Pumps A raw water cooling pump must self-prime reliably at a wide range of engine speeds, tolerating sandy or silty water without loss of flow, and without needing frequent maintenance. JABSCO flexible impeller pumps do the job, often for years at a time, with little maintenance. This is why JABSCO pumps are fitted as standard by marine engine manufacturers worldwide.

What cooling water flow rate does an engine need?
On average, petrol engines and fast-running diesel engines with direct cooling require a raw water flow of about 36-39 litres (8 - 8.5 gallons) per minute for each 75kW (100 bhp) of engine power.  Engines with indirect cooling require more flow: about 65-70 litres (14.5 - 15.5 gallons) per minute for each 75kW (100bhp) of engine power.

Pipework for engine cooling
To provide reliable performance under seagoing conditions, a raw water cooling pump must operate in a correctly-designed cooling system. It is essential that cooling water should reach the pump without having to overcome excessive resistance or restrictions.