How to flush a car radiator
What You'll NeedAntifreeze (1-2 gallons or 4-8 liters)
Step 1 - Get StartedFirst and foremost, make certain that your engine is cold. A hot engine means hot coolant under very high pressure trapped in the radiator - and a possible scalding for you when you remove the radiator cap. Cold water can also damage a hot engine
Step 2 - Clean the RadiatorRaise and securely fasten the engine hood to avoid accidental slippage. Then use your nylon brush and sudsy water to gently scrub away the dead bugs and debris that have collected on the radiator grill. Be sure to scrub in the direction of the radiator fins and not against, as the metal is fragile and can easily be bent out of shape. Once the grill is clear, direct a gentle stream of water from the hose over it to ensure that all debris is completely gone.
Though you only have to flush your radiator once every two years, it's a good idea to clean the radiator grill every 12,000 miles or so.
Step 3 - Place the Drain PanProper drainage of the used coolant is very important. Coolant is highly toxic but has a sweet smell that's attractive to children and animals. It should not be left to drain unattended and should never be allowed to drain onto the ground. Make sure that the pan you use won't be used for any kitchen purposes - a disposable pan is ideal. The pan should also be small enough so that it fits easily under your car.
Once you have found the perfect pan, slide it into place under your car and center it under the radiator's drain valve (also known as a petcock).
Step 4 - Check the Radiator CapThe radiator cap acts as a lid for the radiator, sealing and pressurizing the coolant within to keep the engine cool. The coolant pressure varies from engine to engine, and the pressure rating is indicated on the top of the cap itself.
A radiator cap consists of a spring coil stretched between a wide, flat metal top and a smaller rubber seal on the bottom. The tension between the spring and the rubber seal is what enables the cap to maintain pressure, so if it is easy to compress the two, the cap is worn out and should be replaced. Another sign to replace the cap is any rust or drying of the rubber seal. In general, the cap should be replaced at least every two years, so you may want to make it part of your routine when flushing the radiator. Remember, there are different caps for different pressure ratings, so always keep the rating number in your car's records.
Step 5 - Check the Clamps and HosesThe next step is to check the radiator's hoses and clamps. There are two hoses: one at the top of the radiator that drains hot coolant from the engine and one at the bottom that bathes the engine with cold coolant. The radiator must be drained in order for the hoses to be replaced, so checking them before you flush the engine is always a good idea. This way, if you find signs that the hoses are cracked or leaking or the clamps look rusty, you can change them before refilling the radiator. A soft, mushy consistency is a good indication that you need new hoses, and if you find any of these signs in only one hose, it is still a good idea to replace both.
Step 6 - Drain the Old CoolantThe radiator's drain valve (or petcock) should have a handle that makes it simple to open. Simply unscrew the petcock (while wearing your work gloves - coolant is toxic, remember) and allow the coolant to flow out into the drain pan you placed underneath your vehicle in Step 4. Once all the fluid has drained, replace the petcock and funnel the used coolant into the sealable container you have set aside for the purpose. Then place the drain pan back under the petcock.
Step 7 - Rinse the RadiatorNow you're ready to do the actual rinsing! Simply take your garden hose, insert it's nozzle into the fill spout of the radiator, and let it run until full. Then open the petcock, and let the water drain out into the pan. Repeat until the water runs clear and be sure to funnel all the water used in the rinsing process into sealable containers, as you did with the used coolant. At this point, you should replace any worn clamps and hoses, if needed
Step 8 - Add CoolantThe ideal coolant mixture is composed of 50-percent antifreeze and 50-percent water. Distilled water should be used in the formula, as it is free of the minerals in tap water that could denature the coolant mixture and prevent it from properly doing its job. You can mix the ingredients beforehand in a clean container or pour them in directly. Most radiators will hold roughly two gallons of fluid, so it should be easy to judge the amount you will need to use.
Step 9 - Bleed the Cooling SystemFinally, it will be necessary to bleed out the pockets of air that may have settled in the cooling system. Start your engine with the radiator cap off (to avoid buildup of pressure) and let it run for approximately 15 minutes. Then turn on your heater, and turn it up to hot. This will circulate the coolant and allow any trapped air along with it to dissipate. Once the air is released, the space that it took up will be gone, leaving room for a little more coolant, which you can now add. Be careful, however, the air releasing from the radiator can bubble up and be quite hot.
Then simply replace the cap and wipe off any excess fluid with a rag.
Step 10 - Clean Up and DisposalCheck for any leaks or spills from the petcock, dispose of rags, old clamps and hoses, and your disposable drain pan. Now you're almost good to go.
It is just as important to dispose of used coolant properly as it is to dispose of used oil. Once again, the smell and color of used coolant makes it especially appealing to children, so don't let it sit around long. Transport those containers to the nearest recycling center that handles hazardous materials without delay! See The Expert's About Oil section for more information on disposing of hazardous materials.