The Frugal Car Owner: How to Flush Your Cooling System

Want to save money on your auto care? RelayRides blogger Trent Fletcher shares how to flush your car’s cooling system in today’s Frugal Car Owner.  

We’ve covered a number of different ways to save money fixing your own ride, including changing your oil, rotating your tires, replacing a worn serpentine belt, and swapping out your dead battery. However, one of the vital components we’ve yet to tackle is your car’s cooling system. A radiator flush is a good way to help keep things running cool, but it can cost upwards of $120 on some vehicles at a shop. Fortunately, you can do the same job for literally a fraction of the price in your garage.

Tools You’ll Need

You’ll need some basic hand tools – likely either a Philips head screwdriver or an adjustable wrench, depending on which fastener your radiator uses. You’ll need a container to catch and dispose of the used coolant with, new coolant, and a funnel. Aside from that, it probably wouldn’t hurt to have a couple shop rags around in case of spillage, and if your car is especially low to the ground, you may need to lift it up in order to access the bottom of the radiator, which would require a jack and jack stands.

Drain The Radiator

Before you set out to drain your radiator, it is very important that you ensure that the car has not been driven for at least two hours. Coolant that’s still at operating temperature is very hot, and can burn you if it comes in contact with your skin. Provided the engine is sufficiently cool, it’s time to get to wrenchin’.

Locate the drain valve at the bottom of your radiator. Your owner’s manual should indicate its exact location, or simply looking under the front of the car for a valve or bolt on the bottom of the radiator will probably reveal its location pretty quickly also. After ensuring that there’s enough clearance for your coolant-catching container to be positioned directly under the valve, unscrew that drain valve and let the contents of the radiator drain into your catch container.

Flush the Radiator

Close the drain valve again tightly, then move to the top of the radiator. Remove the radiator cap and check for signs of rust and general wear and tear. Now is a good time to check the large rubber radiator hoses (upper and lower) that are connected to the radiator as well – if any of these components shows signs of brittleness, corrosion, or are otherwise in generally dodgy condition, this is an ideal time to replace those parts. Assuming everything is copasetic, it’s time to flush the radiator.

After removing the cap, fill the radiator with water from a garden hose or several pitchers of water until the radiator is full to the top (where the cap attaches). Once you’ve done that, go back under the car, open the drain valve again, and flush that water back into your catch container. After all the water has drained from the radiator, close the drain valve one last time (tightly).

Add New Coolant

Now back at the top of the radiator, add a mixture of 50% new coolant and 50% water (preferably distilled) until it’s nearly to the top. Leave the radiator cap off, start the vehicle, and allow it to run until it gets to operating temperature. As the coolant heats up, it will expel trapped pockets of air from the cooling system, making room for more coolant. After the vehicle has been idling for 15 minutes or so, top off the coolant again and fasten the radiator cap to the radiator, ensuring it’s making a tight seal with the radiator.

That’s it – your cooling system flush has been completed! Be sure to properly dispose of the used coolant, as it can be harmful or fatal to animals (like pets). Also double check for leaks once you’ve removed the catch container to make sure everything has been tightened up properly. Happy frugal motoring!