What Does Coolant Do In a Car?

The coolant in your car prevents your engine from overheating and freezing. Follow along to learn more about the coolant in your car's cooling system.
Written by John Davis
Reviewed by Melanie Reiff
Coolant is a critical component of your car’s engine cooling system. The system uses a water pump to send the coolant from the radiator to the engine and back again. This cycle keeps your vehicle’s engine at its optimal operating temperature and prevents it from overheating. 
Your car is made up of a series of complex systems working together to keep you moving along the road. Of those systems, the car’s cooling system is one of the most important. But how exactly does it work?
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What is coolant, and what does it do?

Engine coolant works in a way similar to oil: it transfers heat away from the engine and adds antifreeze protection to it
As the power source for your car, the engine gets extremely hot. And with lots of moving metal parts involved, that heat can cause significant damage if not dealt with properly. That’s where your vehicle’s cooling system comes into play. 
At the heart of the cooling system is a water pump, which draws coolant from the radiator and sends it through the engine block, cylinder head, and then back to the radiator. The coolant absorbs heat from the engine, and the car’s radiator releases that heat into the atmosphere. 
Coolant is a combination of water and antifreeze. Antifreeze itself is composed of either ethylene glycol or propylene glycol and contains corrosion inhibitors that protect the radiator and other cooling system components from rust. 
Although antifreeze and coolant are often used interchangeably, there are some slight differences between the two. For starters, car coolant is typically a 50:50 mix of antifreeze and water
The mixture of water and antifreeze to create coolant is vital because water’s boiling point is 212 degrees Fahrenheit and its freezing point is 32 degrees. However, most engines operate above 200 degrees and may occasionally operate in temperatures below freezing. The 50:50 mixture is sufficient to provide cooling at temperatures greater than 200°F and provide antifreeze properties at temperatures of 30° below zero or lower
Key Takeaway Engine coolant is a combination of antifreeze and water used to prevent your engine from both overheating and freezing. 

Does engine coolant go bad?

Engine coolant does go bad, and it needs to be changed periodically. Old coolant can cause a build-up of acid or rust, and it may even lose its effectiveness at preventing boiling and freezing. 
Generally, your car should require a coolant flush every 50,000 miles or so. However, some vehicles only need a coolant service every 100,000 miles, while others might need the coolant changed every 10,000—you should consult your owner’s manual for specific information regarding your make and model’s cooling system and when it needs servicing.  
At least twice a year, you should check your coolant level and condition. Ideally, you should perform this quick check once before the beginning of summer and once before winter. 
When you check your coolant, keep an eye out for the signs that it needs to be changed, which include grimy, oily, or discolored fluid. 

What are the symptoms of a coolant leak?

If not properly and swiftly addressed, a coolant leak can wreak havoc on your engine. Because of this, it’s critical to know the signs of a coolant leak. Some of the most common symptoms of a coolant leak include the following:
  • A sweet smell from the engine. Engine coolant has a characteristically sweet aroma. If you notice a sweet smell coming from the engine bay, there’s a chance your car is leaking coolant. 
  • Puddles of coolant beneath the car. Brightly colored puddles under the vehicle—usually lime-green, orange, pink, or blue-green—are clear indicators of a coolant leak. 
  • Coolant build-up in the engine bay. If you notice dried coolant on radiator hoses or belts in the engine bay, there’s a good chance you have a coolant leak. That, or someone filled the reservoir carelessly and left a mess. 
  • The car overheats. If you notice your car’s temperature gauge climbing too high, there’s a chance your vehicle is leaking coolant. 
All of these issues should be treated seriously, as coolant is a vital part of your car’s cooling system. If the engine temperature gets too hot, it can result in catastrophic damage. 

How often should you add coolant?

You should check your coolant level and condition at least twice a year. If the fluid level is low, top it off. Your car should require a coolant flush every 50,000 miles, depending on the make, model, and production year. 
Trained mechanics usually perform coolant flushes using a special machine that sucks out the old fluid and cleans out any debris before refilling the system with clean coolant. 
A great DIY project that you can do in your own driveway is a coolant drain and fill. Unlike a coolant flush, a drain and fill is when you remove the radiator drain plug and use gravity to drain the old fluid instead of a machine. After the old fluid drains, simply refill the radiator and reservoir with the proper type of new coolant. 
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What is the best kind of coolant for your car?

The type of coolant your vehicle needs depends on a few factors, including your make and model, engine type, and the weather conditions in which you drive. 
You should always check your owner’s manual to learn the particular kind of coolant your car takes. Different automotive manufacturers typically use coolant engineered specifically for use in their vehicles. For example,
coolant is different from
Another factor that plays a role in determining what kind of coolant is best for your car is the weather conditions where you live. While the 50:50 blend of antifreeze and water is generally sufficient to provide cooling and antifreeze properties, if you drive a lot in very cold weather, a 70:30 mix might work better for you. 
Finally, diesel engines require a different type of coolant than gasoline engines. Vehicles with heavy-duty engines, like diesel engines, need a heavier-duty coolant. 
MORE: Antifreeze vs. coolant: what’s the difference?

How to find affordable car insurance 

It’s smart to include checking and servicing your car’s coolant in your car care plan. But it’s just as essential to have a quality insurance policy to protect you and your vehicle in the case of a collision, auto theft, or more. 
Fortunately, shopping for car insurance has never been easier—
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Although often used interchangeably, antifreeze and coolant are slightly different. Coolant is a combination—usually a 50:50 mixture—of antifreeze and water.
Your car needs coolant if the level is low or if the condition is poor. Coolant should be clean and free from grime and debris. Your car’s coolant generally needs to be flushed every 50,000 miles.
You can drive with low coolant, but traveling very far this way is not wise, especially in hot temperatures. If your coolant level is low, you should top it off immediately and then investigate the cause of its low level.
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