DIY Tips: How To Flush Your Radiator


As every experienced car mechanic knows, basic maintenance for your vehicle is key to prolonging the life of your car.  While the easiest step in keeping your car maintained is to simply take it to your local mechanic or dealership service department, that is not always an option. So, knowing how to perform fundamental maintenance to your vehicle is always a good idea, especially with the harsh weather we can have in the Houston area.

While our winters are not typically very hard on our vehicles, Jack Frost does pay us a visit from time to time. Those occasional visits can wreak havoc on our engines and supporting systems. One of the primary culprits for system failure is an engine cooling system that wasn't prepared for winter weather. With this in mind, your friends at Finnegan CJDR offer the following radiator flushing and winterizing tips to help you prepare for whatever weather this winter decides to throw at us.



Always be sure to work on your engine when it is completely cool. This is especially true if you're planning to drain any fluids from the vehicle (oil, water, etc) as a recently running engine will quickly heat up the engine and subsequent liquids to boiling levels. We're sure we don't have to tell you the dangers of exposing your skin to boiling water.

Consider this a safety step, if done correctly. While many vehicle radiators are accessible without this step, the clearance between the bottom of the radiator and the surface of the ground is typically quite small. So, raising the front of the vehicle and bracing it with jack stands is never a bad idea. Besides, elevating the front of your vehicle will help reduce, if not completely eliminate, air bubbles when flushing your radiator.

Back in the day, our grandparents would drain the engine's fluids directly onto the ground and let nature handle the chemicals and toxins.  Today we're a bit more knowledgable on the damage your vehicle's lubricants and cooling chemicals can do to the environment. So, be sure to place a drain pan underneath your radiator to catch everything you're about to drain from your vehicle. Your grandkids will thank you.



Before you start draining the coolant from your radiator, it's always a good idea to inspect the radiator's connecting hoses for any signs of wear and tear. There are two hoses, one on top and one on bottom. Be sure they haven't collapsed at any point as that will restrict the flow of coolant and cause problems with your engine.

Also, it's never a bad step to give the front of your radiator a good once-over to make sure there is nothing clogging or blocking the metal slats, or "fins". If there is anything, simply brush them with a nylon brush until the foreign particles are removed.

Finally, inspect the rubber o-rings on your radiator cap to make sure there is no wear and tear that would prevent the cap from making a good seal when it is closed. If there are any issues with the hoses or the cap, you'll need to replace them.

If the fins are completely clogged or collapsed, you may have a larger problem than a simple flushing can cure. If you have any questions, feel free to ask your mechanic or any of the service technicians as Finnegan CJDR.

The radiator drain valve, or 'petcock', is typically located at the bottom of the radiator and will be the only bolt-looking device there. To open the petcock, use a wrench or socket/ratchet to loosen the valve. Once it is open, gravity will take care of the rest. Just be sure the drain pain is placed where it can catch the fluids.


Draining the radiator will not remove all of the old coolant so a good flushing is required. Here are the steps for flushing your radiator:

  • Use a garden hose to completely fill the radiator with water.
  • Start the car and let it run for 10 minutes. Stop the engine and let the car sit until the engine is cool again.
  • Open the radiator petcock and drain the radiator again. Be advised that this water will contain coolant toxins so handle with care.
  • Repeat this process two or three more times to ensure complete flushing of the radiator.
  • NOTE: you can purchase "radiator flush solutions" from any auto parts store to add to the water as you're flushing the radiator. These solutions aid in preventing rust and oxidation within your radiator. Just be sure to flush out all of the solutions before filling the radiator with coolant.


Close the radiator drain petcock and add your coolant/water mix. You can purchase engine coolant that is pre-mixed with water but if you get the concentrated coolant, you'll have to mix it yourself. A good engine coolant mixture consists of 50% distilled water and 50% antifreeze. It's a good idea to combine the two ingredients in a bucket before adding them to the radiator to ensure a good mix.

It is always a good idea to check the owner's manual for specific coolant requirements or suggestions. If you cannot find that info in your manual, simply bring your car's make, model, and year info to your local parts shop and they should be able to help you.



With the radiator cap still off, start your car and let it run for about 15 minutes with the heater turned on. This action will allow any trapped air to escape from the lines thereby making room for more coolant and preventing any damage to your radiator.  After the 15 minutes are up, replace the cap and remove the jack stand/jack from your car.  That's it, you're done flushing and winterizing your radiator.

We hope these tips will help you keep your vehicle running in tip-top condition year round. As always, if you have any questions or need any help with this or any other maintenance on your vehicle, give Finnegan CJDR's service desk a call. We're always ready to help you.

Categories: Service
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