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Your Vehicle's Engine Cooling System, Simply Explained

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Ms. Millar has been an online writer for over eight years. She is well-versed in website development and has created several websites.

Circulation of coolant

Circulation of coolant

Car Engine Cooling System

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

My aim is to explain the cooling system in vehicles in-depth. The way a cooling system works is similar in all vehicles.

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 ones.

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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 of the radiator through the top radiator hose.
    4. Then the coolant flows through the thermostat.
    5. After the thermostat the coolant heads for the engine. There are passages through the engine for the coolant to flow. It absorbs the engine's heat as it passes through these passages. After the coolant has gone through the engine it is hot and heads for the hoses leading to the heater core inside the vehicle.
    6. When the coolant flows through the heater core (very much like a small radiator) if you turn the heater on inside the vehicle there is a fan that blows across the heater core and the heat is driven off into the cab of your vehicle, thus heating the interior.
    7. 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...
    8. 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.
    9. When the coolant is forced out of the water pump, it heads to the radiator via the lower radiator hose.
    10. Once the coolant is at the radiator, it flows through all the veins in the radiator to the top and it starts its course through the system again.

Cooling System Q&A

SymptomCheck The...Explanation

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.

© 2018 Joanna

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