How to Flush a Car’s Radiator Coolant System

How To Flush A Car'S Radiator Coolant System

Flushing your car’s radiator coolant system is an important maintenance task that should be performed routinely to prevent issues down the road. The coolant, also called antifreeze, circulates through your engine and radiator to keep temperatures regulated.

Over time, coolant breaks down and collecting contaminants that can clog passages and reduce cooling effectiveness. A coolant flush removes old coolant and cleans the system to like-new condition.

In this comprehensive guide, we’ll explain why flushing is necessary, the flushing process step-by-step, and tips to ensure a successful flush. By the end, you’ll be fully prepared to tackle this DIY maintenance job and keep your cooling system running optimally for many more miles.

Why Flush the Coolant?

There are a few key reasons why flushing your coolant every few years or 30,000-50,000 miles is recommended:

Coolant is formulated to last 5 years/50k miles before breaking down. It loses alkalinity and corrosion protection over time. Contaminants like rust and scale build up in the cooling system as old coolant is continuously cycled.

Deposits reduce coolant’s ability to transfer heat, stressing components and risking overheating. Weakened coolant provides less corrosion protection, allowing rust and deposits to accelerate corrosion.

Flushing removes contaminants, restoring coolant’s heat exchange efficiency for optimal temperature regulation and protection. Neglecting flushes can eventually cause leaks, clogs, or overheating issues like a blown head gasket. Flushing is preventative maintenance.

Why Flush The Coolant?
Why Flush the Coolant?

Preparing to Flush the Coolant

Before starting the flush, gather all necessary supplies and ensure you have room to work:


  • New premixed coolant – Use the same type as currently in the system for proper protection
  • Coolant flush chemical – Follows instructions to safely remove deposits
  • Coolant funnel – Directs fluid into the radiator or overflow reservoir
  • Rag or shop towels – For cleaning and absorbing spills
  • Safety goggles – To protect eyes when draining hot coolant
  • Container for old coolant – 5 gallon bucket or larger


  • Park vehicle on level surface with hood access
  • Cover nearby surfaces in case of spills
  • Ensure any pets/children are clear of work area

Also, check the owner’s manual or a repair database for the cooling system capacity. This will determine how much new coolant is needed to refill after flushing. It’s around 10-14 quarts for most cars.

Next, locate the radiator drain plug, usually near the bottom of the front of the radiator. Place the bucket underneath to catch the draining coolant. If it’s been a while since the last flush, the coolant may be quite dirty upon emptying.

Flushing Step 1 – Drain the Coolant

To begin draining, first run the engine for 5 minutes to warm up the cooling system. This allows the coolant to fully circulate and drain more completely. With the engine off and cool, open the radiator drain plug with a wrench or pliers. Let the old coolant completely drain out into the bucket below.

Tilting the radiator can help get the last few ounces out. Once drained, replace the plug hand-tight. Then locate the thermostat housing bolts, usually on the engine near the top radiator hose. Drain the residual coolant leftover in the engine by removing the thermostat housing. Allow this to fully empty as well.

Properly dispose of the used coolant according to environmental regulations. Most auto parts stores will accept small amounts for recycling. With the system now empty, it’s ready for flushing and cleaning.

Drain The Coolant
Drain the Coolant

Flushing Step 2 – Add Flush Chemical

At this stage, introduce a radiator flush chemical as directed. This works like dish soap, cutting through deposits and rust inside tubes and passages. Common flush chemicals include Liqui Moly Radiator Cleaner or Gunk Radiator & Heater Cleaner.

Simply add the recommended amount of cleaner directly into the radiator or overflow reservoir. For a standard system, one bottle or can is usually sufficient. With the thermostat housing still off, the flush solution can circulate throughout the entire cooling loop unrestricted.

Allow it to soak for 30 minutes to an hour depending on the product used. This dwell time allows the cleaning agents to fully work on removing years of accumulated grime. During this process, periodically check fluid level and top off as needed.

Add Flush Chemical
Add Flush Chemical

Flushing Step 3 – Flush the System

To flush the loosened deposits from the system, start the engine and allow the new cooling fluid to circulate. Check radiator and hoses for any initial flushed debris. The first fluid ejected may look dirty or have sediment but will clear as flushing continues.

Let the engine run until the thermostat opens, typically once the engine reaches operating temperature. This fully exercises the cooling loop. Continue running for 10 minutes or more with occasional checks of the radiator drain.

Flush fluid may need topping up to maintain level as it cycles. Repeat this process until the flushed water runs clear, indicating deposits have been successfully removed. At this point, the system is thoroughly cleaned inside.

Flush The System
Flush the System

Flushing Step 4 – Flush with Water

With the majority of deposits cleaned out, it’s time for a final rinse. Drain the radiator once more then refill only with clean water. Repeat the flushing cycle one last time to fully flush any leftover cleaner residues from hard-to-reach areas.

This rinse ensures a contaminant-free starting point for the new premixed coolant. Once the water runs clear with no visible residues, the system is ready for filling with fresh coolant. Drain the rinse water and you’re ready for the last refill step.

Flushing Step 5 – Refill with New Coolant

Nearly done! All that remains is filling the freshly cleaned system with new long-life coolant. Begin by removing the radiator drain plug to allow refilling from the bottom up, reducing air pockets.

Using a funnel, carefully fill the recommended amount of premixed coolant according to your vehicle’s specifications. This usually ranges between 10-14 quarts for most cars. Top off as needed until the coolant level is slightly above the max line in the overflow reservoir.

Start the engine and check for leaks while filling any remaining air pockets. Once full and burped of air, let the engine fully warm up and circulate the new coolant. This allows trapped air to escape up through the system. Check fluid level and top off one final time.

Congratulations, your cooling system flush is now complete! Check fluid levels periodically for the next few drives as the system continues bleeding air. Your engine and cooling components will thank you with improved heat transfer and years more trouble-free operation.

Refill With New Coolant
Refill with New Coolant

Tips for a Successful Coolant Flush

Use dedicated flush equipment when possible for radiators especially clogged. Introducing solution directly aids in chemical contact. If very dirty, you may need to flush in 2 stages – an initial cleaner flush followed by a final rinse flush. This fully removes built-up contamination.

Inspect all hoses for leakage, cracks or swelling during disassembly. Replace as needed to maintain a sealed system. Apply wrenches carefully when loosening bolts to avoid stripping threads. Have replacement parts on hand just in case.

Thoroughly flush complex cooling systems with multiple circuits like on European vehicles to clean out all cores. In cold climates, use an extended life coolant rated for harsh weather to protect to -34°F.

Allow sufficient dwell time for chemical action depending on flush product used as per instructions. Check for coolant leaks within a few weeks of refill to catch any missed seals or gaskets disturbed during service. Periodically inspect coolant condition and flush intervals to maximize service life of new antifreeze.

Signs it’s Time for a Coolant Flush

If your vehicle is outside of the recommended flush intervals, there are some indicators it may need servicing:

Coolant changes color from green to brown/orange as it breaks down over time. Degraded coolant can potentially lead to overheating issues if not addressed. Weakened seals from old coolant increase the risk of small leaks developing.

Smell or sludge buildup inside the radiator means it’s time for a cleaning. Poor heat transfer if the engine takes longer to warm up or interior heat is weaker. Most vehicles could use flushing by 7-10 years/100k miles if service history is unknown.

Signs It's Time For A Coolant Flush
Signs it’s Time for a Coolant Flush

Coolant Flush Myths Debunked

Some common misconceptions about coolant flushes include:

  • You can stretch flush intervals – While true in some cases, neglect increases risk of costly damage from corrosion or overheating down the road.
  • Flushes are expensive – Doing it yourself costs just the price of coolant and chemicals. A shop may charge around $150 which is cheap insurance for long-term preservation.
  • Flush is unnecessary with no issues – By the time problems occur, deposits may have already caused damage. Preventive flushing keeps the whole system protected.
  • You can just top off coolant – Topping off does not remove built-up sludge which continues to reduce heat transfer efficacy over time. Periodic flushing is needed.

Premixed vs Concentrate Coolant

There are also two main options for new coolant – premixed and concentrate that requires water dilution:

Premixed is most convenient as it’s ready to pour but slightly higher cost per gallon compared to concentrate.

Concentrate allows mixing precise amounts needed for your system but requires accurately measuring water ratios which if off can lower antifreeze concentration.

Precautions for Flush Chemicals

Wear gloves, goggles to avoid skin/eye contact as some contain corrosives. Work in a ventilated area and store chemicals away from heat sources.

Follow product SDS for handling, first aid measures in case of accidental exposure. Dispose any leftover chemical as hazardous waste according to local laws.


How do you completely flush a coolant system?

To fully flush the system, you’ll drain the old coolant, remove hoses/thermostat, add a flush chemical to the radiator and let it soak for an hour. Then start the engine and let it circulate, checking fluid for deposits. Repeat circulating with just water until it runs clean. Finally, refill with new premixed coolant.

Can I flush my radiator myself?

Yes, flushing your own radiator is very doable. The process involves draining the system, adding a radiator cleaner, running the engine to circulate it, then rinsing with water. With basic hand tools and following instructions, it’s a straightforward DIY maintenance task that can save you money versus taking it to a shop. Just go slowly and don’t forget to burp air from the system when refilling.

What is the difference between a coolant flush and a radiator flush?

A coolant flush replaces all the antifreeze/coolant in the entire cooling system, including the engine block. It’s a more thorough cleaning. A radiator flush only flushes out the radiator itself, so old coolant can remain in other areas like the engine and heater core. For best results, a full coolant flush is recommended to fully clean the cooling loop.

How much does it cost to flush the coolant system?

The cost to flush your coolant system will vary depending if you do it yourself or pay a mechanic. Doing it yourself requires only basic tool and supplies that cost around $50-75 on average. A shop will charge a diagnostic/labor fee that can range from $150-250 depending on the vehicle and complexity. Overall, flushing every 2-3 years is very affordable maintenance that protects your engine compared to the cost of repairs from neglected cooling system problems.


Properly maintaining your vehicle’s cooling system is essential to its long-term reliability and performance. Flushing the radiator regularly removes contaminants and restores the coolant’s effectiveness. Following the simple multi-step process we outlined ensures a thorough cleanse of the entire circulation loop.

Doing a flush yourself saves money over paying a shop and gives you peace of mind knowing the work was done correctly. Just take your time and double check for air pockets when refilling. The results will be a like-new cooling system protected for many more miles of trouble-free motoring.

Neglecting coolant maintenance always catches up eventually in the form of costly repairs down the road. Staying on top of flushes every 2-3 years using quality parts and fluids keeps everything running at peak efficiency. Your engine will show its appreciation

through reduced heat and smoother operation in any weather conditions. With some basic hand tools and the right chemicals, tackling a radiator flush DIY project builds confidence for additional vehicle care.

Proper disposal keeps contaminants out of the environment too. Taking care of small issues now prevents far greater problems and expense later. Follow these steps to breathe new life into your cooling system!

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