Signs you need a coolant flush: What to look for

Your car has ways of telling you it needs attention. Squeaky brakes generally mean it’s time to replace your brake pads. Your tire pressure light turns on when you need air in your tires. And a check engine light flashing might mean your car has some big problems. But what about signs you need a coolant flush? What should you be looking for?

What does coolant do?

photo of a coolant reservoir

Before we get into the signs you need a coolant flush, it will be helpful to understand what coolant does in your car. 

In a sense, coolant serves as an insulator to your car’s engine. Coolant has the ability to keep your engine BOTH cool and warm… kind of how a thermos or hydro flask keeps your water cool or coffee hot.  Here’s a very quick overview of the three main things coolant does:

1. Keeps your engine cool

As the name implies, coolant keeps your engine cool (duh). As your engine runs, it generates heat and your coolant system (and coolant) helps prevent your car from overheating.

2. Stops your engine from freezing

Coolant is also known as antifreeze. And just as the name implies, it also helps prevent your engine from freezing. If plain water was used to cool your engine, there’s the possibility that it could freeze when temperatures get low. When water freezes, it expands, which could potentially cause damage to your car’s engine.

3. Lubricates your cooling system

Coolant circulates through your car’s cooling system and comes in contact with metal, hoses, gaskets and parts like your water pump. Coolant helps prevent corrosion on the metal parts and prevents wear of the rubber hoses and seals in the system. 

Signs you need a coolant flush

I may be the bearer of bad news, but your car isn’t going to tell you when it’s time for a coolant flush.. It won’t make any special sounds or turn on a warning light to tell you.

To put it another way, there really aren’t pre-programed alerts or “signs” to tell you that you need a coolant flush.

It falls on you to decide when it’s time for a coolant flush. And you can find out the proper time for your car by referencing the owner’s manual. 

It’s just that simple.

But what if you’re not good about adhering to your car’s maintenance schedule?  Or what if you bought a used car and you’re not sure if proper maintenance has been kept up on it? There are a couple things to look out for that could potentially be signs you need a coolant flush….


As your coolant ages, it begins to wear out and it can lose its ability to keep your engine cool. Because of this, your engine can overheat. 

This is the exact reason why you need to flush your car’s coolant! Think about it this way… Parts like brake pads, headlights, and wiper blades wear out on your car and need to be replaced. The same holds true for your car’s coolant (and other fluids like oil and transmission fluid).

A word of caution: Overheating is a serious problem that can cause big problems like a blown head gasket or even a cracked engine block. There are many possible causes of engine overheating and old, worn-out coolant is only one of them. If your engine is overheating, make sure you pinpoint the exact problem and have it properly fixed.

The next possible sign you need a coolant flush is:

Dirty coolant

Keeping an eye on all your car’s coolant levels is a good practice. You should do it every time you’re under the hood. Even if you’re just adding some windshield washer fluid, take a couple minutes to look at all other coolant levels. 

If you spy with your little eye dirty coolant when you are poking around under your hood, it’s a pretty good indication that it’s time for a coolant flush.

As you learned earlier, engine coolant lubricates your engine’s cooling system. As your coolant ages and wears out, it can lose its lubrication properties. Corrosion can start to form and will mix in causing dirty coolant.

oil in coolant

Oil in coolant

If you notice oil in your coolant, it’s not a good sign. It’s an indication of a larger problem with your car. There’s a good chance you will need more than just a coolant flush. Take a look at this article about oil in coolant to learn what it means.

Flushing your coolant is an easy job if you are a DIY’er, no matter what your skill or comfort level. You don’t need special tools nor do you have to remove a ton of parts to access the areas you need to work on. The only downside is that it’s a little time consuming because there’s some waiting time where you need to let your engine cool down.

Before you start the job, be sure to reference your car’s owner’s manual to find out which kind of coolant your car uses. 

Here’s a great video from O’Reilley’s Auto parts that shows what it takes to flush your coolant at home.

How much does a coolant flush cost?

If you are a DIY’er, coolant flush cost is pretty low. You’re looking at less than $50 to do the job. Here are some of the things you’ll need:

What if I want a mechanic to do the coolant flush?

The coolant flush cost if a mechanic does the job for you will run around $100. The cost will fluctuate depending on where you have it done – dealers, local mechanics, and your gearhead friends will all charge different rates.

Three Bay Garage Pro Tip: A coolant flush is an easy add-on when your car is in the shop for an oil change. If, according to your car’s owner’s manual, it’s time for a coolant flush, ask to have it done with your next oil change and save yourself the inconvenience of being without your car two times. 


Don’t wait for signs you need a coolant flush. Your car doesn’t have a built-in way to alert you. A coolant flush is a regular part of your car’s maintenance schedule that you should perform when needed. Reference your car’s owner’s manual to know when it’s time. It’s a pretty simple job you can perform yourself. And if you decide to have someone do it for you, it’s not all that expensive.

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