Your Vehicle's Engine Cooling System, Simply Explained

Updated on January 16, 2019
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Ms. Millar has been a writer on HubPages for over six years. She enjoys the freedom to explore her creative side.

The Role of a Cooling System in a Vehicle

I have been a mechanic for more than twenty years now, almost thirty years. Over the years I have noticed that people do not understand the cooling system and how it works in their vehicle. I have found it challenging to help the vehicle owner to understand the relationship between certain applications and the cooling system.

My aim is to explain, in-depth, the cooling system in vehicles. Vehicles are very similar in the way their cooling systems work.

Circulation of Coolant


Flow of Cool Radiator Fluid

The cooling system in your vehicle's engine does more than just keep your engine cool and the fluid liquid in colder climates. Although these are the main reasons the cooling system exists, they are not the only reasons.

Let's go over the route the cooling system follows in most vehicles when the fluid is at its coolest temperature, which can be upward of 145 degrees. We'll look at how the cooling system affects other components in your vehicle.

  1. The radiator can be considered the first step of the cooling system. Coolant is introduced into the cooling system at the radiator through a capped hole at the top.
  2. Two hoses are attached to the radiator. One radiator hose is at the top, near the right or left side depending on your vehicle's set-up, and another one at the bottom, towards the left or the right, again depending on your vehicle's set-up.
  3. Coolant flows out the bottom radiator hose into the engine. The coolant flows through passages in the engine where it absorbs heat.
  4. At the end of the course through the engine, the hot coolant exits the engine through a hole into another radiator hose.

The Components Radiator Fluid Flows Through

Click thumbnail to view full-size
Location of a water pump.A water pump.A typical thermostat.A serpentine belt running a water pump.A typical heater core.Radiator hoses heading through the firewall to the heater core.
Location of a water pump.
Location of a water pump. | Source
A water pump.
A water pump.
A typical thermostat.
A typical thermostat.
A serpentine belt running a water pump.
A serpentine belt running a water pump.
A typical heater core.
A typical heater core.
Radiator hoses heading through the firewall to the heater core.
Radiator hoses heading through the firewall to the heater core. | Source

The Flow of the Hot Radiator Fluid

  1. The coolant is very hot when it exits the engine. To harness that heat and make use of it, the hose exiting the engine is directed toward the firewall, then passes through the firewall on the passenger side of the vehicle and into another radiator called the heater core located under the passenger side dashboard.
  2. The heater core is another, smaller, radiator that functions just like the one in your engine. It has a pipe for coolant to enter and another for the fluid to exit. The function of this little radiator is to warm the interior of your vehicle and defrost windows when selected by the occupants! As the radiator coolant enters the heater core, it is directed through small veins that run through the heater core. A fan installed on your vehicle can be set to Off, Low, Med, and High. This fan blows across the vanes of the heater core as the hot fluid flows through them, blowing the warm air into the cab of the vehicle. You can use this second "radiator" to further cool an overheating engine during the summer months. Turning the heater on full blast when an engine is starting to overheat will cool the engine. This method has saved many vehicles from overheating. Unfortunately, the occupants must endure the heat that is blowing into the vehicle when it's probably already hot outside.
  3. After the coolant has passed through the heater core, it will still be very hot, even if you turned on the heater. To reduce the temperature of the hot coolant, it is routed towards the radiator at the front of the vehicle. But first...
  4. The fluid is routed to a water pump, whose sole function is to keep the fluid flowing. Without a water pump, the coolant would not flow; there is nothing in the engine itself that pushes it. The water pump is run by a pulley attached to the engine's serpentine belt. This setup ensures that when the engine is running at a high RPM and needs a high flow of water, that's exactly what it will get. As the engine spins faster and faster, the serpentine belt moves faster and faster, thus, making the water pump turn faster and push the coolant faster.
  5. When the coolant is forced out of the water pump, it heads to the thermostat. The thermostat records the temperature of the coolant as it passes through it. A signal is sent to the console inside the vehicle which displays to the driver the temperature it is recording, in real time, to show the driver the engine temperature well before the engine can be destroyed by overheating. The thermostat measures the temperature at the optimum position for recording: after the coolant has passed through the engine, the heater core, and the water pump, but before it has passed through the radiator.
  6. After it leaves the thermostat, the radiator hose heads for the top of the radiator entrance. As the coolant flows through the little tubes in the radiator, like it did through the heater core, the wind from your vehicle moving is blowing over the vanes. There is also a very large fan attached to the engine with a pulley, like the water pump, that blows more air over the radiator veins. This fan blows the air forward away from the engine.

That is the flow of the cooling system.

Cooling System Q & A

Check The...
If the floor is wet on the passenger side floor
Heater core
When a heater core fails it may leak onto the passenger floor where it is mounted above.
If you smell radiator fluid inside your car
Same as above
Same as above
Cold engine: Open radiator cap, turn engine on. Does fluid start to move? If not check...
Water pump and/or thermostat
After an engine warms up, the thermostat opens and the water pump causes the water to flow.
Water pump and/or thermostat
If coolant is blocked by a stuck thermostat, or the water pump isn't pushing the fluid through, the engine overheats.
Do not remove radiator cap if the engine is hot or the hoses are firm when squeezed.
Temperature gauge
High pressure can build up when a vehicle overheats. Wait until hoses are squeezable.
Windshield steaming up for no reason?
Heater core
When the heater core goes bad and leaks, the fluid vaporizes and sticks to the windshield causing a steamy windshield.
Rainbows in the radiator fluid?
The rainbow(s) are oil. There is a leak in the engine allowing oil to get into fluid.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

    © 2018 Joanna


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