To ensure that the Emergency generator engine is standby then it is equipped with a preheater.
The preheater is to keep the engine around 50 deg. C at all times and all conditions. This will ensure that it is will start and can take load as fast as possible.
There are many ways to do this but the most common is to install an electrical heater either direct at the engine block or in the cooling water system. Most simple is to install the heater without a circulation pump and use the natural circulation but in some installation, an electrical circulation pump is required to ensure proper circulation and maybe overheating of the heater.
DEMP have for many years used a simple electrical heater element inserted in the cooling water system without circulation pump. The heater was controlled by on/off switching but today are we able to install new technology using self-regulated heater element and hereby abandon the on/off technology.
In addition is the new heater element not in direct contact with the water and hereby is the chance of getting scale deposits on the element zero and causing overheating leading to break down.