The key reason for using an engine cooling water preheater is to maintain the engine at a temperature to ensure it starts quickly when required. Cold engines can take a considerable time to crank up during which time the starter batteries or high pressure starting air will be heavily discharged. However apart from a starting aid, the heaters provide the following additional benefits:

Reduces engine wear - Engine wear can be reduced by up to 50%. The lubricating oil is also kept warm and thus ensures that the essential oil is immediately pumped to the critical moving parts and points of the engine during the start cycle.

Saves fuel - It is not necessary to leave engines idling to maintain them above the required starting temperature.

Reduced exhaust emissions on start - Engines are designed to emit lower emissions at their operational temperature.

Less stress on other components - Batteries when cold have a reduced ampere hour capacity and starting a cold engine can put a considerable drain on a battery system.

Avoids the risk of water condensation in the engine sump - An engine system left for a length of time in cold temperatures will see an increase in water build up due to condensation. Keeping the engine warmer than the surrounding ambient significantly reduces condensation.

Preheating System:
The preheater and circu­lating pump are placed in parallel with the jacket water main pumps, and the water flow direction is the same as for the jacket cooling water system. The preheater operation is controlled by a temperature sensor after the preheater.

Fig: Engine Preheating System
The preheating pump take suction from just before the main HT water pump and deliver after HT water pump (Just before Engine in). At heat exchanger water can be heated by electric heater or steam. Some components such as- valve, strainer, temperature controller, temperature and pressure gauge also installed.

Fig: Preheater Unit
Fig: Preheater Unit

Preheater capacity:

When a preheater is installed in the jacket cooling water system, the preheater pump capacity, should be about 10% of the jacket water main pump capacity. It is recommended that the pres­sure drop across the preheater should be approx. 0.2 bar. The preheater pump and the jacket water main pump should be electrically interlocked to avoid the risk of simultaneous operation.
Fig: Preheating time Vs Capacity curve

The preheater capacity depends on the required preheating time and the required temperature increase of the engine jacket water. The temperature and time relationship is shown in Figure abobe. The relationship is almost the same for all engine types.


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  1. Hi, Really great effort. Everyone must read this article. Thanks for sharing.


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