How The Cooling System Works 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. The way a cooling system works in a vehicles is similar in all vehicles.

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 of the radiator through the top radiator hose.
  4. Them 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 engines 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.

If your vehicle is over heating you can use the heater core like a radiator to help cool the coolant. Turn the heater on full heat and high fan and it will blow heat off of the heater core. You will see a decrease in the temperature, but it won’t completely stop the engine from overheating, but it will give you a few extra miles to find a safe place to pull over.

Q & A of the Cooling System

Q. The floorboard on the passenger side is wet all the time. What is it?

A. The heater core is going out or already has gone out. It’s leaking radiator fluid on the floor. The windshield may also become foggy from the steam escaping the heater core which is located under the dashboard on the passenger side.

Q. It smells like radiator fluid in the car often. Why?

A. Same as above. The heater core is bad or going bad and the radiator fluid is leaking into the passenger side and emits the odor of radiator fluid.

Q. How can I determine if the water pump is working?

A. When the engine is cold, open the hood and remove the radiator cap and set it aside. You can now see down inside the radiator. You should be able to see the radiator fluid. If you cannot see the fluid, add some until you do. Now turn the engine on.

(CAUTION: Pull your hair back, remove your tie and/or any other loose clothing or jewelry! You will be near the engines moving parts, wear nothing that could become tangled in moving parts!!)

A. Continued…Now that the engine is running, go back to the radiator and look at the water inside the hole where you removed the radiator cap. The water should be jostling around from the engine vibration, but not a whole lot. As the engine warms up keep watching the fluid. At a certain point the engine will become warm enough to activate the thermostat. When it does you will see the water in the radiator begin to swirl around aggressively because the water pump is pushing the water through the system. If the water never begins to swirl around aggressively, and the temperature gauge indicates HOT then your thermostat is not opening, or your water pump is not working.

Q. Why does my car overheat?

A. It is overheating either because the thermostat is not opening up to allow all the coolant to flow through the system, or the water pump isn’t working as stated above. There may be debris in the radiator blocking the system as well. This all depends on the age and condition of the radiator and hoses.

Q. Why is there rust in the radiator?

A. There is rust in the radiator because metal develops rust when it is exposed to water. If you had put coolant into the radiator it would not have rust. Coolant protects the cooling system from rust, as well as cooling the system efficiently.

Q. Why does the coolant fluid have rainbows in it?

A. The rainbows are oil in the coolant fluid. This means there is a leak in the system and the coolant is being contaminated by the oil. This condition is also known as “A blown engine”.

Q. Why do I have to wait before removing the radiator cap?

A. If you remove the radiator cap when the vehicles engine the fluid inside can blow out super hot. The pressure inside builds up as the fluid gets hotter. The radiator cap and hoses are under a high pressure when the engine is hot. You can squeeze the upper radiator hose to determine how much pressure is in the system. The radiator hose in normal conditions is squeezable. When it is under pressure it is hard like a baseball. Wait until it is squeezable before removing the radiator cap.

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