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What does a Car Radiator do?

Michael Pollick
Updated May 23, 2024
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To understand what a car radiator does, it might help to understand the nature of the internal combustion engine it protects. A car's engine has numerous moving parts, and where there is movement there is friction. Friction creates heat. Motor oil is pumped throughout the engine block to provide some lubrication, but it isn't enough to overcome all of this excess heat energy. As a result, parts of the engine become boiling hot as part of normal operations.

This is where the radiator system comes into play. The engine block must be kept relatively cool to avoid serious problems like overheating and seizure. If the pistons cannot slide freely in their cylinders due to excessive friction, they will eventually snap and cause total engine failure. To prevent this from happening, a mixture of water and anti-freeze is pumped through chambers in the engine block to absorb the excess heat and draw it away from vital areas.

When this superheated engine coolant exits the engine block, it returns through a large rubber hose. This component is designed to maximize surface area through a significant number of internal folds and chambers. As the hot engine coolant moves through these nooks and crannies, excess heat is drawn out through the walls. An electrical or belt-driven fan may force cooler outside air through the radiator to accelerate this cooling process. As the car moves, the front of the radiator is also cooled by the outside air coming through the car's grill.

By the time the superheated engine coolant has made its way through all of the chambers, it should be cool enough to make a return trip through the engine block. However, if the coolant flow should be reduced by a blockage or loss of fluid, the engine block will not be cooled down and the remaining engine coolant will boil over. This is why maintaining a full coolant level is so important, especially during hot weather or long drives.

A radiator does not contain any electronic parts of its own -- special sensors register the temperature of the coolant as it exits. Engine coolant does not have to be especially cool in order to be effective, so there is usually a wide range of temperatures considered to be within normal parameters. If anything goes wrong with the radiator itself, such as a leak or broken hose, the operating temperature of the car can reach a dangerous level within minutes. The engine must be allowed to cool down naturally before the vehicle can be driven safely to a mechanic.

WikiMotors is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Michael Pollick
By Michael Pollick
As a frequent contributor to WikiMotors, Michael Pollick uses his passion for research and writing to cover a wide range of topics. His curiosity drives him to study subjects in-depth, resulting in informative and engaging articles. Prior to becoming a professional writer, Michael honed his skills as an English tutor, poet, voice-over artist, and DJ.
Discussion Comments
By anon253111 — On Mar 08, 2012

I have a 2006 Dodge Grand Caravan. During cold weather, sometimes smokes or steam (can't tell which) comes out in small bits from either the front of the car or the front left side (right in front of the windshield) and there's a distinct sweet smell.

I had it in for an oil change and they checked the fluid levels and said everything was fine. The engine temp rises only very slightly from normal operating temperature when the smoke appears and if I turn on my heat full blast the smoke/steam goes away.

By anon247148 — On Feb 13, 2012

@Kansas 07: You have probably figured this out by now, but here goes anyway.

You say "both radiator hoses were sucked tight like all the air was sucked out of them". We have been having problems with overheating recently on our Rover 75 (at the moment it is intermittent) and I spoke to one of the garages that deal with Rovers and they explained that if the rad pipes are old they will need replacing as over time they lose rigidity. If they don't have rigidity then the coolant cannot flow through them (i.e. they are sucked closed) and then the engine overheats.

So if you replace the pipes that may solve your problem?

By landonlewis — On Jul 26, 2011

Summer driving is a lot of fun but you have to be sure that your car is in good condition. Is your automobile's radiator prepared to conquer the summer warmth? Don’t let the long, hot summer beat down your vehicle's radiator. Deposit buildup can block the cooling system and result in motor overheating that leaves you dead on the highway. If you know the way to flush your radiator, you can save time, money and keep on the road to summer sun.

By anon199307 — On Jul 23, 2011

water is always coming and steaming out the overflow even when car is running at the right temp. does anyone know about this?

By kansas07 — On Jan 25, 2011

I have a 99 isuzu trooper and we are having overheating problems. I am not bragging but we are pretty good mechanics, we know what to do for the most part. We changed the thermostat the water pump and the clutch fan. We did it one at a time and after every replacement we get closer and closer. before we would only drive a quarter mile before overheating. We have took infrared heat temperatures throughout the motor and heads and all. all temperatures are close or right on.

We checked down in the pistons and oil, no moisture, no signs of head gasket leaks. It can idle all day with out overheating. We can drive forever but every half mile the gauge goes up close to hot than if i step into it the thermostat opens up and cools back down. The heat kicks ass, well cools down when it starts to get hot but kicks right back on.

A couple of times, I popped the hood and noticed both radiator hoses where sucked tight like all the air was sucked out of them. Any ideas? Sorry for the long post but I figured I'd say it all at once.

By anon133415 — On Dec 10, 2010

I have a used 98 Chevy Malibu LS. For a while the low coolant light was on but i didn't know what it was. I thought it was oil so i checked and it wasn't it. I drove the car from Richmond, Va to Norfolk, VA and everything without knowing it was low on coolant.

A couple days later the car had steam coming from the antifreeze tank. I stopped pulled up the hood and checked everything. Saw there was only water in the coolant tank and put in some antifreeze. It's like five days later and it's still doing the steam thing and sounds like it's boiling under the hood when I drive. Is it the radiator?

By anon132815 — On Dec 08, 2010

if the engine's coolant temperature goes above 98degree centigrade and there is not any type of oil cooler mounted, then what is the condition of oil found and temperature also?

By anon130966 — On Nov 30, 2010

please tell me does the heater in your car run by petrol or does it run off the battery?

By anon94245 — On Jul 07, 2010

1 have a 1998 ford mustang gt and i been having a problem of the water being drained out of the radiator.I took the radiator to clean, changed the thermostat and the water pump. Then i took it too the mechanic and they said it could be the heads so i replaced them. But i still have to add water to the radiator everyday. There's is no leak so i don't know what it is. Can anybody help me out?

By anon86619 — On May 26, 2010

I have a 1998 chevy malibu and lately it has been running hot. First we changed the water hose, then we changed the thermostat. Now I'm so lost, because no one knows what else it could be.

I don't want to burn the motor or anything major. And then we heard that sometimes when you buy a used car you have to change a lot of things, so now we are going to see about cleaning the radiator. Can you please help me understand what it could be?

By anon83356 — On May 10, 2010

What makes a car radiator boil over? I have replaced the radiator, radiator cap, upper radiator hose, lower radiator hose, thermostat, thermostat housing, water pump, hose clamps, belts, water and gaskets.

The radiator still boils over and escapes out the overflow tube and completely and totally purges. Antifreeze seems to be a complete and total waste of money. I've gone so far as to open the fan clutch and added new heavy viscosity oil! Nothing works! What have I missed? Regards, Tony

Tampa Bay, Florida

By anon77828 — On Apr 15, 2010

I have a 1990 Chevy P/U 4.3 Liter V6. Cooling system has not leaks, internal or external. Engine runs hot, but not to the point of boiling over.

Replaced thermostat twice, replaced upper and lower hoses (both in rough shape) and replaced the water pump. Also flushed radiator with GUNK radiator cleaner. Still no success. Checked engine temp gauge and replaced engine temp sensor.

The top hose on the radiator is not hot at all, and that side of the radiator is cold. The side with the lower hose is hot. Think it's a clogged radiator that needs replacement?

By anon61875 — On Jan 23, 2010

should the reserve tank be vented at the top side?

By anon50353 — On Oct 28, 2009

I have a 1992 Cadillac Deville. I run the car for awhile, I shut off car, and coolant is boiling into the reserve tank. Any ideas what this could be? Ive already tried a new cap and thermostat. what else could it be?

By pollick — On Sep 22, 2009

The coolant inside a radiator can become boiling hot after the engine runs for a relatively short time. The cap on a hot radiator is under a lot of pressure and is holding back a lot of steam and hot fluids. The radiator won't "explode" if you remove that cap, but it will spew steam and hot fluid everywhere. Never remove a radiator cap until the radiator has had a chance to cool down. For the poster with the Windstar, I'm wondering if you have enough coolant and water in the radiator itself to prevent evaporation. The radiator system will draw additional coolant from the reservoir as needed, but if you're already running low, it will take every last drop and still require more. When the engine is completely cool, open the radiator cap, not the reservoir tank, and check the coolant level. A mechanic could also check this for you, along with the proper ratio of coolant to water in the radiator.

By brandan1 — On Aug 28, 2009

I drive a 2001 Ford Windstar and it went dry and I filled the reserve up with water and it took a lot of water. in just a short while the water was gone. there are no leaks and yet no water. what can cause this? Thank you, mary

By anon41667 — On Aug 16, 2009

should you only check the radiator coolant after the car is completely cool? my brother said it will explode if you check it after driving, is that true?

By anon36817 — On Jul 15, 2009

now a days what is used in place of a radiator?

By anon33618 — On Jun 09, 2009

As said in the article above: "The engine must be allowed to cool down naturally before the vehicle can be driven safely to a mechanic." My car is suspected of leakage of coolant in the radiator and when i drove it for a test drive to prove that it is the case within around 4km of driving there is smoke coming from the car. So i decided to go to a mechanic to get it fixed, the problem is would it still be wise to drive it to the mechanic or get it towed there. And because, as said above that temp. could go up to a dangerous level within minutes then would it be better for me not to drive it. Last, what does it mean to let the engine cool down before driving it, how much time is sufficient to drive it to the mechanic? Your would be much appreciated. Thankyou

By anon31255 — On May 02, 2009

I have a 95 Isuzu rodeo I'd just bought and the the car runs great except that I started seeing a leak, maybe oil or transmission fluid. I took it back and they told be that there was a hose leaking from the radiator where the oil and the transmission go in to be cooled off. I'm no expert but that didn't sound right. They said they replaced the hose and put new clamps at no charge. Next day no leak so far, but does this explanation make sense?

By anon24627 — On Jan 15, 2009

since the topic appears to be the cooling system, I would like to know how some auto cooling systems pressurize the system when there is no (visible) radiator (pressure) cap? Is the system pressurized by an internal (to hose or radiator) pressure valve?

By anon24236 — On Jan 09, 2009

to the person that asked about the flow direction, and to the person that says it does not matter, and to the person that says check the cold hot areas of your radiator, gravity is the answer, it comes in through the top pipe and enters the radiator at top level, if the coolant level is low it pours in to the radiator, if it was the other way round then how can the water pump suck in water from the top pipe if there is no water behind it when the water system is 1 liter low, also if the engine is running and the water temperature is cold/warm and you opened the radiator cap there would be huge pressure being forced up from the bottom towards the cap and it would overflow hence the flow going opposite the cap end to the bottom with the aid of gravity, really hope this helps. GOGS.

By anon21766 — On Nov 21, 2008

can coolant bought from an auto shop be mixed with water after its been poured into the reserve tank? A colleague told me that that would cause corrosion in the radiator.

By anon17874 — On Sep 09, 2008

Thank you for your explanation. Ours is currently blocked (only about 10 open slots) with a cracked reserve tank (superbonded for now). We are working on getting a new one, but living on an island takes a little longer. Is it safe to drive short distances for now, while letting it cool naturally in the interim? Also, does running the heater help relieve some of the pressure?

By anon13922 — On Jun 06, 2008

This will explain how the reserve tank works. I was searching for how much the system increased the boiling point of water. It seems it is about 45 degrees F.

By zumzum — On May 20, 2008

in car radiators how does the reserve tank work? water is going from the reserve tank to the radiator or from radiator to reserve tank? how is it actually working if it is going from reserve to radiator? how it is possible because water outlet is above from the water level? help me pls

By anon11534 — On Apr 18, 2008

The water flows from the top to the bottom of the radiator.

Also the article implies that the heat comes from friction. Only a very small amount of the engine heat is generated by friction. Most of the heat in a combustion engine is generated by the exploding (petrol/diesel) gasses that generate the power.

By anon6851 — On Jan 10, 2008

Which way does the coolant flow through the radiator? Top to bottom, or bottom to top?

By anon6022 — On Dec 13, 2007

As someone who knows nothing about vehicles, i found your article to be of much use. My car was overheating, and the mechanic explained the radiator, and radiator hose was bad. i have decided to look up some of the basics on maintaining a vehicle....As far as "superheated" goes, i decided to take the info as it is, instead of criticize...People, find something to do. This isn't a vocabulary debate.

By anon4669 — On Oct 27, 2007

Some engines use a pressurized cooling system where water temperature is allowed to rise above 100 degrees celsius.

By thermogeek — On Oct 04, 2007

I stand by my critique of the word choice in using "superheated". The article uses "superheated" while describing the normal operation of a car cooling system rather than a failure mode. How is the coolant in this condition excessively heated or overheated? The dictionary definition is technically faulty and confusing in stating "...without causing vaporization". It should say something like "passed above the saturation state" instead. In technical usage, superheated means the substance is completely in a gaseous state (no liquid at all). Here is a fair technical definition (if you replace the word water with liquid): Superheated steam, steam heated to a temperature higher than the boiling point corresponding to its pressure. It

can not exist in contact with water, nor contain water, and resembles a perfect gas; -- called also surcharged steam, anhydrous steam, and steam gas. If you still don't believe me, then call a (rankine cycle) powerplant engineer and ask: "what kind of water spins the turbines?"

By anon4120 — On Oct 03, 2007

Why do you use the term "superheated" rather than just "heated" or "hot"? To say water is superheated means that all of it is in a gaseous state. A mixture of gaseous and liquid water is referred to as saturated. Engine coolant would have to be boiling to even get up to the saturated state.

A thermogeek.

Michael Pollick
Michael Pollick
As a frequent contributor to WikiMotors, Michael Pollick uses his passion for research and writing to cover a wide range...
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