Do-it-yourself instructions for maintaining a car's coolant system

Just because it's spring doesn't mean you can ignore the antifreeze content of your car's radiator. If your car radiator has ever boiled over because of a dirty cooling system, you know how expensive it can be for a new thermostat, new radiator cap, and complete professional back-flushing of the system.

What's worse, if you haven't drained, flushed, and replenished the coolant in the last two years or 24,000 miles, you could be in for problems again -- not only from internal rust buildup but from a diluted water-to-antifreeze mixture that could lead to a frozen engine or cracked block next winter.

For maximum safety, convenience, and economy, take a few minutes to check and maintain the cooling system.

Here's what you should know about coolant protection and the steps you can take to drain, flush, and replenish the car's coolant in the cheapest of all manners -- the do-it-yourself way.

Today's modern auto engine is designed to maintain efficient operating temperatures with ethylene glycol (permanent antifreeze) solutions.

New cars have factory-installed ethylene glycol antifreeze coolant, which will afford protection against freezing in the winter and protection in the summer (because it raises the boiling point of the water), and contains corrosion inhibitors to protect the cooling system year round.

Under recommended service conditions, the antifreeze coolant will function for at least a year.

Although ethylene glycol, the antifreeze agent in the coolant, does not evaporate, it loses its effectiveness in time, particularly when it is diluted repeatedly with water. You've probably added water to your radiator from time to time to keep it filled -- a natural tendency when you see the level getting low. And it does! A perfectly good system will leak a pint every 1,200 miles.

Unfortunately, adding just water ruins the antifreeze concentration to the point where overheating and freezing protection is lost.

It's a much wiser practice to add a half-and-half mixture of antifreeze and water, a mixture that can be made up in advance and kept indefinitely in an old antifreeze container. And don't think you're boosting protection if you add more than 50 percent antifreeze; this actually increases the freezing point.

A 100 percent antifreeze solution, for example, will freeze at only -8 degrees F. instead of the normal -34 degrees F. offered by a 50 percent solution.

Any time you see dirt particles floating around or notice that your coolant is rust-colored -- or both -- it's time for a radiator flushing, no matter how few miles you've driven since the last one. If your car's coolant is in this condition, chances are also good that the car needs a new mixture of water and antifreeze, too.

You can check the percentage of ethylene glycol in the coolant by using a radiator antifreeze hydrometer, which is available at most auto centers for less than $5.

Always conduct your coolant check when the engine is cold. Just remove the radiator cap and look inside. If your car has a coolant recovery system, you do not have to remove the radiator cap to check the coolant. Simply glance at the translucent overflow reservoir.

Draining and flushing the cooling system can be done by either of two methods:

The usual method almost always requires you to jack up the car. It also puts you in closer contact with a hot engine. While more complicated and time-consuming, this method is the most economical and calls for only common tools and a radiator flush additive.

The ``hassle-free method'' can be performed without jacking up the car, and there is less danger of coming in contact with a hot engine. Although safer, faster, and easier, the hassle-free method is more costly, since it requires the use of readily available flushing aids or a flushing kit. It is still more economical than a professional drain-and-flush job, however.

To determine which method is better for your car, refer to the ``engine cooling system'' section of the owner's manual.

As a final consideration, pick a spot that's safe and suitable for your drain-and-flush effort. Dirty coolant will soak into a dirt or gravel surface, but it will flood a concrete floor. Usual method

Remove the radiator cap, but first be sure the ignition is OFF and the engine is COOL.

Open the petcock at the bottom of the radiator.

Remove the engine-block drain plugs with a wrench. The plugs are approximately at the base of the exhaust manifold (in-line engines have one plug, while V-6s and V-8s have two, one on each side of the engine block).

When the engine block is empty, tighten the petcock and reinstall the drain plugs.

Using a garden hose, fill the radiator almost to the top with water. Add a can of fast-flush solvent (available at most auto centers). Run the engine for about 20 minutes at fast idle and with the radiator cap off.

Turn off the ignition and drain the system again as in the second and third steps outlined above. Leave the petcock open and the plugs out.

Place the garden hose in the radiator filler neck, and flush with water under pressure.

With the hose still running, start engine and let run at fast idle for at least five minutes before turning it off.

Tighten the radiator petcock and replace and tighten the drain plugs.

Mix correct proportions of water and antifreeze, and fill the radiator.

(If your car is equipped with a coolant recovery tank, remove the tank first and clean it inside and out with soap and water. After it's reinstalled, fill the radiator to the base of the filler neck and raise the level of the coolant in the recovery tank to the ``full hot'' mark. Reinstall the recovery tank cap.)

Replace the radiator cap, start the engine, and let it idle for a few minutes. Turn engine off, remove radiator cap, and check to see that the level of coolant is correct.

Replace the radiator cap and tighten it securely. Check for leaks from the drain plugs and petcock. Hassle-free method

This method requires the use of a commercially available flushing kit or flushing aids. Typical components include a deflector, flushing ``T,'' hose clamps, and a hose coupler. These items are readily available at most auto centers for less than $5.

Set the heater temperature control to ``high.'' If your car is equipped with a vacuum-operated heater valve (check with your auto dealer if you're not sure), run the engine at idle during all flushing procedures described.

The vacuum-operated heater valve, found mainly on newer-model cars with factory-installed air conditioning, will stay open only with the engine running. Keep an eye on the engine-temperature gauge.

Open the radiator drain petcock, and let the water run out. Do not open the engine drain plugs.

Remove the radiator cap, and put a deflection elbow in the filler neck to prevent any excessive splash into the engine compartment.

Locate the heater hose, which runs from the firewall to the engine block. Actually, there are two heater hoses, one to the water pump and the other to the block.

Cut the heater hose in two near the firewall, insert a T-fitting, and tighten the two hose segments to the ``T'' with hose clamps. (The ``T'' will always be in place when you want to flush the radiator in the future.)

Remove the ``T'' cap, install the hose coupler, attach the garden hose to the coupler, and turn on the water full blast.

Flush the system for three to five minutes.

If your car has a vacuum valve, the engine should be running. The flowing water will force the coolant in the engine back through the system passages and up through the radiator. Simply let the water back-flush the system until the water flowing out of the radiator is clear and obviously clean.

Turn off the water, remove the hose, replace the ``T'' cap, and close the radiator petcock.

Proceed with refilling the radiator under the ``usual method'' section above.

Replace the radiator cap and tighten it. Check for leaks around the petcock.