Every so often, it is good to flush your car's cooling system to prevent buildup of dirt and debris that may lead to rusting and cause mechanical problems. Flushing the coolant is something that should be done once every year or so, and is a great project for the not-so-amateur mechanic.
Diagnosing the state of the coolant
If checking the oil rates highly among your automotive skills, this job may be better left to a professional. However, you should still know how to check the coolant for signs it needs to be changed soon. The first step is to ensure there is enough coolant. This can be done simply by visually inspecting the antifreeze reservoir to see if the fluid levels are high enough. Some cars do not have reservoirs, so you'll need to consult the owner's manual to determine your vehicle's standings if you are unsure. If there's no reservoir, you'll have to remove the radiator cap and examine the fluid inside this chamber.
If the coolant appears rusty, clear, or filled with sediment, it is time to flush the system. If the liquid has an oily sheen or a sludgy appearance, you may have a faulty head gasket on your hands. This situation is best left to the professionals.
Collecting the necessary tools
As with almost any automotive maintenance, you're going to need a few tools if you plan to flush the radiator at home. First, get some new antifreeze - one or two gallons. You can purchase this premixed or add your own water, just be sure to use distilled water if you choose the latter option. You will also need a bucket to drain the old fluid into, another bucket with a bit of soapy water, a garden hose with a nozzle, a soft-bristle brush, waterproof work gloves and safety goggles.
Now that you've got your tools, make sure the car has had ample time to cool down since you last drove it. Coolant is designed to reach high temperatures, so care must be taken to avoid accidentally scalding yourself. Pop open the hood, grab the soft-bristle brush and the soapy water and clean off the radiator grill. Be sure to scrub gently, as the grating is usually delicate and can easily be bent out of shape. Once you're done, spray it down with the hose to clear the grill of all the loosened debris.
Draining the fluids
First, remove the radiator cap. Be sure to examine it for signs of rust or other damage and replace if necessary. Place your drainage pan or bucket underneath the car and then open the drain valve, which is also sometimes called a petcock. Once the coolant stops flowing, close the valve and fill the system up with water from the hose. Let that drain out and repeat the process until the water runs clear.
Check the hoses before refilling
When the system is empty, take the time to inspect the radiator hoses and clamps for signs of wear and replace as necessary. Then, you can start adding the coolant. If you're mixing the antifreeze and water yourself, the recommended rule of thumb is equal parts of each. So, if you add a gallon of antifreeze, add a gallon of water. Just be sure to mix them together before you pour them into the car to ensure they're blended properly.
Bleed the system
When you're done refilling, start the car and let it run for a few minutes to ensure any air in the system is bled out. You should have a bit more room for coolant, so add some before replacing the radiator cap and you're done.