Coolant Drain or Flush: Which Is Better for Your Car?

Stephen Fogel
June 1, 2018

Your car’s coolant is responsible for keeping your engine from overheating, which would create very expensive problems. But coolant doesn’t last forever, and you’ll need to change it out eventually. 

Image courtesy of Wikipedia/EvelynGiggles

There are typically two ways to do this: a drain or a flush. But what are the differences between the two? And which is better for your car? Let’s look closer at what coolant does, or you can jump ahead to learn more about coolant drains, coolant flushes, and which one to choose in your situation.

What coolant does

Coolant is a mixture of antifreeze and water. As it circulates, it absorbs the intense heat generated by the combustion process in your engine. The coolant then goes through your radiator, where it releases that heat. This is a continuous process that keeps your engine at an optimal operating temperature, for good fuel economy and smooth running. 

Your coolant has other protective jobs to do as it circulates through your engine. Its high alcohol content protects against freezing at low temperatures and overheating at high temperatures. Additives blended into your coolant prevent corrosion, rust and mineral deposits from forming in your cooling system.

Coolant deteriorates over time. As it ages, it starts losing its ability to prevent rust and corrosion. If neglected, the buildup of corrosion and contaminants can cause damage and system failure. Coolant will also lose its ability to protect your engine from extreme temperatures. 

This is why a coolant replacement service is part of every vehicle’s maintenance schedule. You can find this schedule in your owner’s manual. Depending on when your car was made, it might need servicing anywhere from every 30,000 miles to every 100,000 miles. 

The coolant service usually involves draining the old coolant and putting new coolant in. But many auto service shops will recommend a coolant flushing process instead. Both of these coolant service procedures replace your old coolant with fresh coolant, but in different ways. Let’s take a look at both and see which makes more sense for your car.

» MORE: Get an estimate for a coolant change 

What is a coolant drain?

The traditional coolant draining process is also known as “drain and fill.”Â  This involves simply draining the coolant at the bottom of the radiator, then topping up the radiator with fresh fluid until it it’s full. It’s quick and easy, and while it doesn’t remove all of the old coolant from your system, it is often all that’s necessary to keep your cooling system healthy.

What is a coolant flush?

The coolant flushing process is more complicated, and will likely be more expensive than a drain and fill. A flush differs in the following ways:

  • It uses a chemical cooling system cleaner and conditioner
  • It uses high pressure to “power clean” your entire cooling system
  • It removes old coolant, dirt, rust and other deposits

Instead of letting gravity do the work, flushing uses water pressure to blast any accumulated bad stuff out of the cooling system’s passageways. Both the radiator and the engine block are cleaned out. The final step is to add new replacement coolant.

Get your car diagnosed by a professional

Should you get a coolant drain or flush?

A lot of shops want to flush your cooling system whenever you have it serviced. But this isn’t usually necessary. Here are a few simple guidelines for whether you should drain or flush your coolant.

Follow the manufacturer’s recommendations

Check your owner’s manual or warranty booklet to see what the manufacturer recommends. Most will simply say to change the coolant, which usually means a drain and fill. If you have a pretty new car, or you’ve been punctual with your routine maintenance schedule, your car should be just fine with this. 

When a coolant flush may be needed

If the manufacturer recommends flushing your cooling system at certain intervals, then definitely do it. Make sure that any instructions that the manufacturer specifies for this procedure are followed.

If you have an older, possibly neglected vehicle with a cooling system problem, a coolant flush is the best way to go. This is particularly the case if your coolant has become contaminated with corrosion, rust or debris. 

If your coolant looks dark and murky, or has particles floating in it, you’ve probably waited too long to service your cooling system. The same goes if you see oil in your coolant. The bad coolant should be completely flushed out and replaced with fresh replacement coolant. If your head gasket is bad, that needs to be dealt with at the same time. This is definitely a job for your mechanic. 

Keep in mind that your cooling system needs to be working well before you flush it. This means that any leaking or overheating issues must be repaired first, before performing the flushing procedure.

Keeping your cooling system healthy

Regular preventive cooling system maintenance will eliminate the need for more drastic — and expensive — measures. If you follow the service schedule and do the drain and fill when recommended, you should be able to avoid a situation where a flush becomes necessary.

Bonus tip: It’s a great idea to replace both your thermostat and your radiator cap whenever your coolant is drained or flushed. These parts typically aren’t expensive, but if they fail, they can cause overheating.


Stephen Fogel

About the Author

Stephen has been an automotive enthusiast since childhood, owning some of his vehicles for as long as 40 years, and has raced open-wheel formula cars. He follows and writes about the global automotive industry, with an eye on the latest vehicle technologies.

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