Do I Need a Coolant System Flush?

By Chris Hardesty 06/26/2023 4:00pm

Engine coolant

Coolant System Flush Quick Facts

  • Flushing coolant removes contamination that can cause engine overheating.
  • Flush your coolant according to the manufacturer’s maintenance schedule, or check the system if you notice signs that point to potential problems.
  • The cost to flush coolant is likely less expensive than repairs caused by engine overheating.

A car’s cooling system may be among the most neglected components when it comes to service and maintenance. Delaying or omitting regular service on a car’s cooling system can contribute to an unplanned stop on a steep grade. Or, the neglect could cause the cooling system’s contents to pour onto your driveway, which is not good for the car, the driveway, or your wallet.

Ignoring your vehicle’s cooling system needs can lead to problems, resulting in necessary repairs. If left alone, it may cause a blown head gasket or a cracked engine block, which will cost considerably more than this routine cooling system service.

What Is a Coolant Flush?

A radiator flush or coolant flush is a procedure that drains and replaces the antifreeze in a vehicle’s cooling system. Flushing coolant is a routine maintenance service that removes rust, sediment, and scale deposits that can cause overheating. The clean antifreeze added during a coolant system flush can help maintain your car’s optimal operating temperature.

Signs You Need a Coolant System Flush

The maintenance schedule in your owner’s manual indicates when you should plan to have radiator fluid replacement service. However, you should check the cooling system immediately if you notice unusual symptoms. You might need a radiator flush if the following occurs:

  • A syrup-like smell comes from the engine
  • The car overheats when the coolant level is full
  • You hear engine knocking or grinding sounds
  • The coolant has visible debris
  • Leaking fluid accumulates underneath your car

How Does an Engine Become Overheated?

So, let’s start with the basics. Your cooling system circulates coolant (not just water, but more on that later) through your engine to control its temperature. Engine combustion of fuel and friction from moving parts creates heat, and the cooling system provides a counteraction to that heating.

Coolant flows throughout the engine, and the radiator cools it. In the interim, coolant flows through the radiator hoses, the heater core, and the water pump. If any of those elements becomes clogged or fails, or if coolant runs low, there is potential for an overheating engine and the resulting breakdown.

Keep your system filled to the indicated line on the cooling system reservoir. Most reservoirs have two fill lines noted on the side; one for when the engine is cold (the lower line on the reservoir) and the other for when it is at operating temperature. Overfilling the system is wasteful since excess coolant will bleed off through the overflow outlet.

Never take the radiator cap off unless the engine is completely cool, or hot coolant will erupt under pressure. Always fill the cooling system through the reservoir. When the engine warms up, it will draw the fluid into the radiator. After a day of driving, recheck the reservoir level and top off as needed.

When To Flush Your Coolant

The simplest way to avoid overheating is to service the system according to your owner’s manual recommendations. Flushing the coolant and replacing it with fresh fluid every two years or 30,000 miles is a good rule of thumb, but guidelines can vary from model to model.

While you perform this service, inspect the hoses and radiator cap for wear. Replace hoses that are soft to the touch, show signs of wear, or are over five years old. Be sure to inspect the large top and bottom radiator hoses but also any heater hoses that connect to the heater core.

The radiator cap can lead to overheating all on its own. Through pressurization, the cap allows the coolant to operate at temperatures that would normally cause it to boil over. This is why your radiator can operate at 240 degrees Fahrenheit rather than fail at water’s usual boiling point of 212 degrees. Inspect the cap to make sure the spring is not rusty and that the rubber gasket that contacts the radiator inlet is not dried out or damaged.

Benefits of Getting a Coolant Flush

Replacing antifreeze cooling fluid removes deposits and contamination that can block the even flow of coolant that keeps the engine running at a good temperature. A clean cooling system with fresh coolant lowers the likelihood of expensive repairs from engine overheating.

A Word About Coolant

Coolant and antifreeze are generally interchangeable terms since both come in the same bottle. If you buy coolant, it has antifreeze properties — and vice versa. Coolant keeps your engine from overheating. Antifreeze keeps your cooling system from freezing when the engine is off. For purposes of this discussion, it’s all coolant.

If you live in extremely cold climates, you may need to adjust the percentage of coolant/antifreeze to water. You might also invest in an engine block heater. Ask your local mechanic or dealership technician for specifics relative to your location.

Many years ago, radiator systems chiefly used water alone to cool the engine. Today, a 50/50 mix of coolant and water will deliver the best protection. Coolant manufacturers have bottled their products in two ways: 100% coolant you must dilute with water, and pre-mixed half-coolant half-water solutions.

TIP: Be careful not to purchase the 50/50 mix solution and then add water to your system, or you will dilute its effectiveness.

What Is Engine Coolant Made of?

Coolant is chiefly made of ethylene glycol, regardless of its color, which can vary among manufacturers. Always follow your carmaker’s recommendation for replacement coolant.

Aftermarket coolant is generally green or orange but can come in other colors like blue, yellow, purple, or pink. If your vehicle uses an orange coolant, it’s intended for extended-term use and contains additional rust inhibitors. It is not interchangeable with standard green coolant.

How To Flush Coolant

In the past, do-it-yourselfers would flush their cooling system in their driveways. Several companies today still offer aftermarket flush and fill kits. The kit allows you to insert a “T” fitting into the heater hose and connect a garden hose for clean water. After draining out the coolant by opening the petcock at the base of the radiator, the garden hose would force cool water through the engine, water pump, hoses, and radiator to remove scale and debris.

However, we do not recommend this DIY procedure because changing your coolant at home is extremely toxic to humans and pets. Also, proper disposal of used coolant is crucial because emptying the fluid in your garage or driveway could allow it to end up in the water system.

Instead, have your coolant flush performed by a professional shop. If you refill your coolant at home, make sure to clean up all spills and drips, as ingesting even a small amount can cause illness.

How Much Does a Coolant Flush Cost?

A coolant flush typically costs between $200 and $250 at a dealership, depending on the vehicle, your location, and other factors. Your neighborhood mechanic can likely flush coolant systems and most brick-and-mortar service centers will do the job. Always ask about discounts, especially if the coolant flush is combined with another service.

Nobody enjoys spending money at the auto shop, but following the carmaker’s maintenance schedule can help minimize cooling system failure and avoid expensive radiator repair.