Electric water pumps are used on automotive engines to replace belt driven water pumps. Belt and direct drive water pumps have been the norm since water cooled engines were first developed, but electric powered water pumps are now an option for some vehicles.
Air cooled engines
Originally, all internal combustion engines were air cooled. Most engines had cooling fins and some also had a fan that directed air across the fins to aid in cooling. As internal combustion engines grew larger, it became more difficult to keep them cool. A larger engine produces more heat. More heat requires more cooling fins and air flow to dissipate it. Eventually you reach a point where you expend a large amount of the engines potential power just to turn a fan to keep it from overheating.
Aside from the fans and fins problem, air cooling requires a lot of space. In the old days, internal combustion engines were large stationary devices. They were used in factories and farms to run machinery. Small size was not an important requirement. When automobiles started to come into existence, small size became a much bigger priority.
Off the top of my head, I can’t think of a single front engine air cooled car that was successful. The most successful cars with air cooled engines were the Volkswagens and the Porches. Both of these cars were rear engine cars and both incorporated engine driven fans, ducting, and cylinder cooling fins. Most auto makers adopted water cooled designs to save space.
Water cooled engines
Although you have to add a radiator, water cooled engines still take up less space. When you change an engine from air cooled to water cooled, you need to add a water pump, hoses, a radiator, and water passages. This might seem like it would make water cooled engines take up just as much space, but there are other space saving advantages to consider.
The biggest space saving advantage to going water cooled is that you can put the cylinders right next to each other. In air cooled arrangements, you need to leave room between every cylinder for air to flow between the cooling fins and cool the cylinder walls. This adds a tremendous amount of space required for the final dimensions of the engine. This is why you see old airplane engines with a “radial” layout. They have cylinders with cooling fins spaced equidistant from each other around in a circle. This is to ensure that each cylinder is far enough away from the next one for it to receive adequate cooling air flow. If this type of engine were water cooled, the cylinders could be right beside each other separated only by fractions of an inch.
Water cooling enabled new engine layouts
Once the kinks were worked out of liquid cooling an engine, many new options became possible. Prior to liquid cooling, a V layout engine such as a V8 cast from a single engine block would not have been possible. Inline or “straight” style engines cast from a single block were also not possible. These types of engines are now the most common and found in every type of vehicle. If the cylinders on these engines needed to be cooled by air, they would be impossible to produce.
Electric water pumps
The next step in the progression of engine cooling development seems to be electric water pumps.
Up until the last decade or so, all water pumps were powered by the engine itself. This is usually done by a V-belt that is turned by the engine crankshaft which then turns the impeller of the water pump. Some designs incorporate a mechanical linkage, or diaphragm pump, but the vast majority of engines use a belt and impeller setup.
The drawback of these systems is the power they take to run them. A traditional style water pump setup robs the engine of power that it could otherwise be using to move the vehicle. Not only does the engine need to turn the impeller through the water in the pump housing, it also has to overcome the added rotational mass of the water pump pulley, the friction of the water pump bearings, and the slippage of the water pump belt. Some mechanical water pumps can take as much as 10 horsepower to turn.
The idea with electric water pumps is that they are more efficient. An electric water pump doesn’t introduce any of the losses associated with the belt and pulley setup. An electric pump bolts right on to where the normal manual pump would go, but it doesn’t have any means to spin it on the front like a normal pump would. Instead, it comes with wiring that is hooked up to the battery and the ignition switch.
Horsepower losses with electric water pumps still exist. Running an electric water pump doesn’t completely eliminate the power needed to operate your cooling system. The electricity needed to run your electric pump has to come from somewhere. That somewhere is your alternator. Your alternator will need to generate more electricity to power your water pump, and therefore it will generate more drag on your engine. The benefit outweighs the drawback though as you can use up to 75% less horsepower to run an electric water pump over a mechanical one.
It’s not all great news. Electric water pumps do run more efficiently, and do improve your gas mileage, but they also cost more and are less reliable. Many people are concerned about putting an aftermarket electric water pump on their car because they are not as reliable as a mechanical pump. This will improve as these pumps become more common. The price point of these electric pumps will also come down as they are adopted by more auto manufacturers. We are just at the beginning of the switch over.