What is a Radiator Flush?

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  • Written By: Michael Pollick
  • Edited By: Bronwyn Harris
  • Last Modified Date: 16 June 2019
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Over time, solid deposits can form inside a vehicle's radiator system, causing blockages that make the circulation of the coolant much less efficient. As a result, the vehicle runs hotter and other systems become damaged by the excessive heat build-up. One way to avoid such a problem is to periodically perform a maintenance procedure known as a radiator flush. During this procedure, the original coolant is drained from the radiator and replaced with a special coolant/detergent mixture and fresh water. As the solution circulates through the vehicle's cooling system, it dissolves and removes any solid build-up inside the radiator channels. The coolant/detergent is then drained and replaced with a standard mix of coolant and water.

Many people take their vehicles to a professional auto mechanic or radiator specialist for a radiator flush. Many "quick oil change" companies also offer it as an optional service or as part of a package of services. The process itself can take a few hours, since the vehicle's existing coolant must have time to cool down completely before it can be safely drained into an approved container. The mechanic will also have to run the engine with the coolant/detergent until it reaches normal driving temperature, then run the vehicle's heating system at its highest setting for a period of time. The coolant/detergent then needs to cool down before it can be drained and replaced with standard coolant and water.


A professional radiator flush can be a fairly expensive procedure, depending on the service provider and the type of coolant required. The benefit of a thorough flush, however, is an engine that runs much cooler and a more efficient radiator system. Unlike an oil change or other routine maintenance, this procedure is not based on mileage or yearly maintenance schedule. At some point in a vehicle's history, especially if it is running hotter than usual for long periods of time, the radiator should be flushed and the coolant should be fully replaced.

A radiator flush is not a difficult process to perform, but it needs to be done safely and in a precise order. An experienced home mechanic should be able to complete the procedure in one day, as long as he or she has a proper receptacle for the old coolant and cleaning solution, a screwdriver or wrench to remove and replace the drain plug, a supply of clean water, new coolant/anti-freeze, and the detergent solution.

The radiator's drain plug should be located along the bottom of the radiator's front section. Depending on the type of radiator, the plug may require a screwdriver or wrench to remove. The home mechanic should place the receptacle under the drain plug before removing the drain plug. It is vitally important that the engine be completely cool at this point. Once the drain plug is removed, the old coolant should drain into the receptacle. This liquid should never touch the ground or be left near pets or small children. Engine coolant may taste sweet to a pet, but it is highly poisonous.

The next step is to replace the drain plug and open the radiator cap. The mechanic should pour the entire contents of the coolant/detergent solution into the radiator through a funnel, then top it off with clean water. After replacing and tightening the radiator cap, the mechanic should start the car and allow it to heat up to normal operating temperature. Once the car reaches that temperature, the mechanic should turn on the car's heater to its highest setting and allow it to run for at least 15 minutes. This will allow the coolant/detergent enough time to circulate through the entire radiator system and remove any solid deposits.

The car should then be allowed to cool down completely before moving on to the next step. Using the same approved receptacle or a different one, depending on capacity, the mechanic should remove the drain plug and allow all of the coolant/detergent to drain out. Once all of the coolant has been drained, the mechanic should replace and tighten the drain plug and open the radiator cap. Using a funnel, the mechanic then adds the new coolant and water in a 50/50 ratio to the radiator until it is completely full. Once the radiator cap has been replaced and tightened, the car should be safe to operate.

Disposal of the old coolant and cleaning solution may depend on local laws concerning hazardous materials. Performing a radiator flush or oil change at home may not be easy, but it can represent a significant savings compared to having those procedures performed at a commercial auto repair shop.


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Post 3

The heater core runs hot all the time in modern cars, The heat distribution is achieved by air flaps redirecting airflow over the matrix in varying degrees. This system also acts as an additional heat sink to help cooling, turning the heater on or off makes zero difference to flushing the coolant. The "highest setting" merely means the flaps are directing more air over a permanently hot matrix.

Post 2

@ Submariner- If you are doing a radiator flush, you should also check all of your hoses and clamps and change the thermostat. The thermostat only takes about twenty minutes to change, and will cost less than twenty bucks. You might as well change any cracked hoses and rusty clamps when there is no fluid in the system. These extras will not add much time to your car repairs, and will offer better peace of mind. Your car will also look nicer under the hood.

When I change my radiator fluid, I also like to check my belts, pulleys, plugs, wires, and replace my air and fuel filter. A few beers and a half a day is all it will take.

Post 1

Engine coolant flushes are easy home repairs that any amateur mechanic or handy person can perform. The process is only time consuming because of the time spent waiting for the vehicle to warm up and cool down.

The most important aspect is safety, and disposal because of the toxicity of radiator fluid. If you have a weekend day off, you can perform a radiator flush oil change, and bleed your brakes in a couple of hours.

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