How to Flush a Clogged Radiator the Quick & Best Way

Have you ever experienced a severe engine overheating? It could be due to a clogged radiator or blown head gasket, which could lead to other engine problems. A clogged radiator is usually caused by a cooling system that hasn’t been serviced or flushed for a long time or due to contaminated or old radiator antifreeze.

A fluid that has been in your radiator for a very long time without running your engine or one that has not been changed for long will attract rust and sediments that clog radiator finds and pipes. In this article, I’ll show you step-by-step how to flush a clogged radiator so you will save hundreds of dollars from maintenance costs.

How to flush a clogged radiator step-by-step guides:

A radiator flush is an essential part of car maintenance. Your radiator helps in cooling your engine. So, it is necessary you flush it as the manufacturers recommend. You shouldn’t wait until you notice symptoms of a partially clogged radiator or symptoms of a completely blocked radiator before flushing it.

symptoms of a partially clogged radiator

To flush your clogged radiator yourself, you need the following;

  • Distilled water
  • Chemical radiator flush
  • Catch pan
  • Coolant/ Antifreeze
  • Funnel
  • Disposable gloves and
  • A mechanic tools box. You’ll need some common hand tools.

Step 1. Park your car and allow it to cool down: Before you touch your cooling system at all, whether it is opening the radiator cap, whether it is opening the radiator petcock, or it is losing any water hose, always make sure that the system isn’t hot. Always make sure that the system is cool because you don’t want to burn yourself.

Some cars might not have a radiator cap or a coolant reservoir tank. So, whatever I explain using the radiator cap, you can always do it through the reservoir tank. A couple of days before flushing your clogged radiator, you might want to pour a liter of chemical flush in your radiator and run it some days before flushing your radiator.

Step 2. Empty your coolant: You want to empty your coolant. Grab your catch pan and slide it under your car. You want to make sure it stays directly under the radiator petcock. Lose the petcock to enable the old coolant to flush through it. The petcock is usually at one end of your radiator, usually the lower right or left side of the radiator.

If your radiator doesn’t have a petcock, you can grab your pliers and unclamp the down radiator hose, so the coolant will easily flush through. If the coolant is not running fast via the petcock, one trick I learned years ago, lose your radiator cap and watch the coolant flow more quickly. Lock the radiator drain petcock once the coolant has completely drained out.

Step3. Refill your radiator with distilled water: you want to refill the radiator with a distilled water and get the best radiator flush chemical and in the radiator. Twist your radiator cap to lock it. Make sure you don’t damage it because a bad radiator cap will also cause an engine to overheat. Drive your car for about 15 minutes, so the chemical flush will dissolve the clogged contaminants in the system.

Step 4. Drain out the coolant: Slide your catch pan under the vehicle and drain out the coolant. As the radiator is draining out, one thing that is not going to drain is the coolant reservoir tank. If you open the coolant reservoir cap, you’ll see that the coolant is therein. You’re going to remove the coolant reservoir hose that connects to the radiator cap. Bend the hose to the ground. Ensure it points directly to the catch pan so that you won’t spill the coolant on the floor.

Find a way and suck the coolant to start flowing to the ground. Remember, you want to recycle all flushed flush, all the antifreeze. This fluid is poisonous to animals. If your dog or cat happens to drink it (which does taste sweet), they will die. Repeat this process until you see clean water coming out of the radiator.

Step 5. Flush the outside fins and pipes with a steam machine: If the outer radiator fins are blocked, you want to flush it out. Depending on your car, you can decide the lose out the radiator coat or radiator fan, so you can adequately flush out the debris and sediments on the putter radiator fins. Fix the back whatever you take off the way and proceed to the next step.

Step 6. Pour your antifreeze: the next step you have to take after you notice clean water coming out of the radiator and ensure that the outer radiator fins are unclogged, you have to pour in your antifreeze. I recommend using a 50/50 antifreeze. You don’t have to add water, just the antifreeze. Before you add in any antifreeze, you have to conduct your owner’s manual to know the right antifreeze to use.

You have to make sure you add some sealing agents to seal off any openings on the radiator. Once you’re done, you have to drive your car for like 10 minutes. Ensure you blast your heat to max. If you don’t feel the heat coming from the heater core, it means the heater core is clogged. So you have to unclog it. This guide is on how to unblock the radiator.

If you’re looking at flushing the radiator with vinegar, you have to isolate the radiator from your car. Block off the upper and lower radiator hose. You can use think nylon and a rubber clamp to block off the radiator hose. Take a gallon of vinegar and pour it into the radiator and allow it to stay for about four hours in the radiator. Once the four hours have elapsed, you have to flush the old vinegar through the petcock. The next thing you want to do is lose the down radiator hose and flush your radiator with a hose by connecting it to a running tap.

The next step is to fix back everything that you take off the way. You have to make sure everything is in place. Pour your coolant and idle your car for few minutes, ideally, 5-10 minutes.  While the vehicle is running, ensure you blast your heat.

how to clean out your car radiator


How do you unclog a clogged radiator?

Unclogging a clogged radiator might be a pretty easy job for you if you’re a DIY enthusiast. To unclog a radiator, you have to remove the radiator cap. Open the draining petcock. Get a catch pan and allow the old fluid to flush into the pan. Fill the radiator with distilled water and add a flushing chemical. Start the car for 10 minutes. Ensure you blast your heat. You might decide to take a short drive with the vehicle. Once the ten minutes elapsed, drain out the fluid. Repeat this process till you see clean water coming from the petcock.

What is the best thing to use to flush a radiator?

As a have known, a radiator is an essential component of your car cooling system that sediments your heating water from causing an overheat. To flush your radiator, you’ll be needing a chemical coolant flush. I recommend using a Simple green pro HD heavy-duty cleaner. I have used this cleaner several times, and it gives an excellent flush experience.

Can flush a radiator cause problems?

Well, the answer to this can be yes or no. No, because radiator flush is meant to clean debris and contaminants in the radiator. And, yes, because the goal of a radiator is to flush out debris, rust, corrosion, and other contaminants in the radiator system. If the flushing fails to clear out those rusts and contaminants after dissolving them thoroughly, they might end up blocking other parts of your cooling components, including the radiator itself.

How do you unclog a heater core?

If you have concerns that your heater core is clogged over years of driving, you should unclog it before it leads to another damage. Opening a heater core is a pretty easy job. You need a water hose, some heater core flush kits, long nose pliers, and a water pump to blast water into the heater core. Once you have all these close by, remove both hoses connected to the heater core and connect the heater core flushing kits to the water hose.

Socket the water hose to the heater core pipes and blast the water in. As you are blasting the water from one end of the heater core pipes, the water will be coming out from the other pipe.  You can flush the water from both sides of the pipes until you see clean water coming out. Once you notice clean water coming out, you have to reconnect the hose the way it was. You have to ensure there are no leaks; you don’t want to create a problem where there is none.

How do you know if a radiator is clogged up?

As your car engine runs, it generates much heat, both inside and outside of your engine. The purpose of the radiator is to keep the engine at optimum operating temperature. When the radiator is clogged, not working, or has completely gone bad, not even inside the engine is going to maintain a standard operating temperature. This can result in engine overheating, and if not taken care of, it can cause a blown head gasket or other internal engine issues. So, once you suspect a clogged radiator, check out for these signs;

  • Antifreeze leaks
  • Blocked radiator outer fins
  • Damaged or bent radiator fins
  • Fluid discoloration
  • Faulty heater on the passenger side.
  • High-temperature gauge

Will a radiator flush fix a clogged radiator?

Yes, a radiator flush will fix a clogged radiator. What is the goal of flushing a radiator if not to remove rust, debris, contaminants, and corrosion within the radiator? You want to use the best radiator chemical flush.

Final word.

I believe this article has clearly explained how to flush a clogged radiator. So, next time you notice any signs indicating a clogged radiator or clogged heater core, you can easily flush it out without seeking the help of a professional mechanic.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

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