Understanding how a vehicle’s water pump works

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On almost all cars, the water pump is operated by the crank shaft or by something that is driven by the crank shaft. As your piston slide up and down in the cylinders of your car, the rods on the opposite end are constantly pushing on the crank shaft causing it to spin.

The spin of the crank shaft transfers the energy generated by burning fuel to all of the moving parts of your car.


Most of the energy goes toward the transmission to make the car move. By the use of belts, small amounts of this energy is transferred to the alternator for electrical generation, the power steering unit, the air conditioner, the pollution control pump, and the water pump.

Today, very few water pumps on cars pump much water.


A better name for the water pump would be the coolant pump. Over the years, the liquid flowing through your car’s engine has become less and less water. Improved coolants keep your engine corrosion minimized and increases the cooling ability your engine’s system. It used to be that antifreeze was mixed with water in proportions great enough to keep the water from freezing in cold weather. Today’s coolants do not always call themselves antifreeze since this is just a small part of what these products do for the engine.

A belt from the crank shaft pulley drives the water pump.


This belt may drive only the water pump, or it may serve to drive nearly all of the devices on the front of the motor. Either way, the water pump is a centrifugal pump. It has a shaft that extends through the center of the housing. On the outside, this shaft has a pulley to allow it to be spun. In the middle of the pump the shaft passes through bearings that hold it in place and let is spin as freely as possible. At the far end inside the water pump is the impeller. This looks like a miniature version of the paddle wheel on an old water driven grist mill.

Water enters and leaves the pump by means of hoses and ports.


Usually, a radiator hose and heater hoses attach to the exterior of the water pump. The ports on the back of the pump match up with the ports that connect to the internal cooling pathways throughout the lower half of a car engine. The oil cools most of the upper half.

One of the ports will relate to the location of the thermostat.


When the thermostat is closed, the engine is cool and coolant circulates without going through the radiator. When it is open, the heated liquid pours through the radiator to dissipate some of its accumulated heat before returning to circulate through the engine. A portion of the heated liquid flows through the heater hoses to and from the heater core inside the cabin of the car to warm it up on cold days.

The water pump has internal gaskets to keep the coolant from leaking out along the shaft.


These gaskets keep the coolant inside of your car’s system. If the gaskets start to fail, your water pump has a weep hole that will begin to let coolant escape. This is usually the first warning that it is time to replace your water pump. Most of the time, if the gaskets are leaking, it is because the bearings are about worn out, too. It is best to just replace the pump before it fails completely when this sign appears.


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