Step 1: Clean the radiator front and fan

Your vehicle's cooling system sucks in air as you drive, which means insects, dirt and leaves can be pulled into the fins of the radiator fan. This condition prevents air from passing easily through the radiator, and can cause your car to overheat.

Raise the engine hood. You need both hands for this job. Ensure that the hood is fixed securely in an open position. Your head will thank you.

Using a hose with a nozzle, a bucket of soapy water and a soft nylon brush, loosen the dead bugs (which likely will be crispy critters from all the radiator heat) and the other debris. Brush with the direction of the fins of the radiator fan, not against it. These thin metal fins are fragile and can be bent with this action if you're not careful.

Follow this gentle cleaning with a gentle stream of water on the front and rear of the radiator. Don't turn up the hose to full pressure--a concentrated blast of water can be actually bend the fins of the radiator.

In general, you should clean the radiator fins every 12,000 miles (19,000 km). Don't do it when the engine is hot; cold water can damage a hot engine. Wait until the engine has cooled before you start cleaning.

Step 2: Place the drain pan

Never allow coolant to drain out onto the ground. Its sweet smell attracts animals that will drink it. Don't leave it to drain unattended in a pan, for the same reason.

Buy an inexpensive pan just for this purpose or use a pan that is no longer used in the house. Don't rummage around in your kitchen for the Christmas turkey roast pan. Antifreeze-flavored foods aren't so tasty.

The pan should be big enough to hold the coolant, but not so deep that it doesn't lie flat or slide easily under your vehicle. Tipping a pan on its edge (to slip it into position) is a bad idea. It will only lead to spills.

The location: Get down and have a look. Make sure that the pan is centered under the radiator's drain valve (called a petcock) from where the coolant will flow.

Step 3: Remove the radiator pressure cap

Cover the radiator cap with a rag. You've made sure the engine is cold, but go slowly anyway. Most radiators now have a fill spout that is slanted slightly towards the windshield of the vehicle to avoid mishaps, but caution is never wasted.

Put on eye protection and sturdy, preferably waterproof gloves.

Never lean over the radiator when removing its cap. The contents of a radiator can be under pressure even with a cold engine, and you don't want any unpleasant surprises.

With the heel of your hand, press down firmly, turn the cap a quarter turn to the left. You'll feel the cap is loose when you move it, but it's still locked on. (This first turn is to release any pressure in the radiator.)

Then, pressing down once more, turn the cap another quarter turn to the left and take it off.

Step 4: Inspect the radiator pressure cap

The radiator cap acts as more than just a lid for your radiator; it keeps your engine cool by sealing and pressurizing the coolant inside. And not all caps are the same--they are made to maintain a variety of pressure, depending on the size and type of engine. How do you know the pressure rating of your cap? It's written on the top of the cap. When you replace it, make sure you get one that has the same rating. When you buy a new one, take the old cap into the store with you if you aren't exactly sure.

You will notice that the cap has three main features. The wider top of the cap, the smaller seat at the bottom (with a rubber seal) and a spring coil in between. This spring is what seals the cap to maintain pressure. If you squeeze the seat and the top together, and it's very easy to compress the spring, then replace the cap. It isn't doing it's job.

If your cap is rusted or the rubber seal is dried out, it should be replaced.

Here's a good rule: if you haven't replaced the cap for two years, make this small investment and you'll avoid a larger problem.

Set aside the cap on a clean spot...You won't need it until you're done with the flush.

Step 5: Inspect the clamps and the hoses

There are two radiator hoses you'll want to check. The hose at the top of the radiator carries the hot coolant away from the engine, and the hose at the bottom carries the cooled coolant back to the engine. These hoses may be on either side of the radiator, but they're always opposite each other. Don't put this off--check before you continue with the flushing. Changing the hoses requires that you drain the radiator first--so checking the hoses before you refill the radiator will prevent an unnecessary second draining.

Inspect the radiator hoses for leaks, cracks or soft, mushy condition. Look for signs of rust on the clamps that hold the hoses.

If you find one bad hose, the other hose will probably go bad in the near future. Because the coolant must be drained to replace the hoses, it makes sense to replace both at the same time. But don't actually replace the hoses until you drain the radiator.

Step 6: Drain the radiator

To drain the radiator, you'll need to locate the petcock, which is the radiator's drain valve. You'll find it on the bottom of the radiator, and you'll notice that it has a handle. That handle is there for a reason: you won't need a wrench to open it (although you have one handy just in case).

Open the petcock. As you open this valve, the coolant will start to flow from the radiator into the drain pan you placed below it.

Allow enough time for all of the coolant to drain out, and then close the petcock.

Using the funnel, pour the drained coolant into a container that meets the disposal regulations in your area. Set it in a safe place while you continue this project.

Step 7: Rinse the radiator

Oddly enough, the actual rinsing of the radiator is the easiest part of the entire operation. Your garden hose does all of the work--you just pay attention to the color of the rinsing water as it leaves the radiator.

Take the garden hose and insert it into the fill spout.

With the petcock closed, fill the radiator until full. Then open the petcock and drain it once again. Important: collect this first rinse and dispose of it in the same manner as the drained coolant. That is, add it to the disposal containers that you have for Step 6.

If the drained water is clear, close the petcock and move onto Step 8. If it appears rusty, continue filling and draining until the water is clear. After the first flush, it's all right to let the rinse water drain on to the street.

Close the petcock.

Alternate Step 7: Rinse and replace a hose

Have you removed the bottom hose to replace it? Don't put the new one on until you've rinsed out the radiator. In this case, you want to rinse the radiator with the petcock always closed. (If you're replacing a top hose, go ahead and replace the hose and follow the procedure described above).

Hold your gloved hand over the hole on the radiator where the bottom hose attaches.

Fill the radiator with the hose.

Release your hand quickly. The water will gush out and any rust or mineral deposits will escape through the larger opening of the hose. Repeat this until the water runs clear.

Replace hoses and clamps as needed. Fortunately this is a simple matter--just unscrew the old clamps on both ends of each hose, and the hoses come right off. And installling the hoses is the same motions in reverse.

Step 8: Add the coolant mixture

The optimum coolant combination is a 50/50 mixture of antifreeze and water. Any greater concentration does not significantly increase the efficiency of the coolant. Actually, the more antifreeze you add above 50 percent, the lower your protection becomes. The 50/50 mixture will produce freeze protection down to -34F (-36C), and boilover protection up 250F (121C).

Although regular water will do, the refilling of the system should be done with distilled water. Why bother with the extra expense? Distilled water doesn't contain any minerals which can dissolve and turn the coolant into a corrosive compound.

There are three ways (at least) to refill the radiator:

Fill the radiator halfway with water. Can't see into the radiator? Estimate the amount of water based on the amount of coolant that you drained out. If you drained out two gallons (8 liters) of coolant, then you need to add one gallon (4 liters) each of water and antifreeze.

Using a funnel, fill up the radiator with antifreeze.

A second way:

In a separate clean container, mix antifreeze and water in a 50/50 ratio.

Add the 50/50 mixture until the radiator is full, and store any extra coolant.

A third way:

Pour in a half container of antifreeze. This usually comes in one-gallon (4 liter) containers, so add a half-gallon (2 liters).

Add to the radiator an equal amount of a distilled water. Then mix water into the antifreeze container (which still has antifreeze in it). This will create the 50/50 mix, which you can add to the radiator until it's full.

It's good idea to have a little extra coolant after this fill-up, because the coolant level will drop slightly after you do Step 9. The excess from this step can be used to top off the radiator a little later.

Step 9: Bleed the system

It's probable that pockets of air will be in the cooling system after you've refilled the radiator. The system is self-bleeding when you follow these steps:

Start your engine, but leave the radiator cap off so the pressure doesn't build up.

Let the engine run until it reaches its operating temperature of about 190F (88C). This'll take about 15 minutes.

Turn on your heater and set the temperature control to hot. This will circulate the coolant and any air in the heater lines and core.

Check the level of the coolant. You may find that the level has gone down some. How did that happen? The air trapped in the radiator kept the level artificially high; when this air was released, it opened up more space in the radiator, and allowed more antifreeze into the system. Add more water and antifreeze, in the same 50/50 ratio, to fill the space left by the bled-out air.

As the air bleeds out, the coolant may bubble and spit from the opening on top of the radiator. Use caution--that coolant is hot.

Step 10: Replace the radiator pressure cap

Basically, this isn't too tough--you replace the cap in reverse of how you removed it. It's important, however, that you get it on tightly. The cap has two wide tabs, opposite each other on the cap, hanging down slightly. Measured across, each tab is about one quarter of the circumference of the cap. The fill spout, where you poured in the coolant, has two notches or cutouts that match up with the tabs of the cap.

Match the tabs with the cutouts on the fill spout. Press down firmly on the cap and turn it to the right a quarter turn. Give it a jiggle to be sure it's in place. Though the cap shouldn't be tight at this point, you shouldn't be able to lift it off, either.

Turn the cap another quarter turn to the right, still pressing down, until you feel it lock into place. It should be locked tight now and won't move if you try to wiggle it.

With a rag, wipe around the cap to clean off any coolant that might have sputtered out. That coolant smells awful if it's left there to burn off!

• 1-2 gallons (4-8 liters) of antifreeze
  
• 1-2 gallons (4-8 liters) of distilled water (make sure it's distilled)
  
• (The amounts of these fluids depend on the type of vehicle, and the size of the engine and the radiator)
  
• A drain pan or pail
  
• A garden hose with a nozzle and a water supply
  
• A pair of waterproof work gloves
  
• A soft nylon brush
  
• A bucket of soapy water
  
• A pair of safety goggles or safety glasses
  
• Proper disposal containers (non-beverage containers that are clearly labeled and can seal tightly)
  
• Three or four rags (old undershirts and underwear work great)