Most cars have a plastic coolant recovery tank (top of photo) connected to the radiator by a hose, so there's no need to open the radiator cap itself (orange label at bottom). The coolant level should be at the tank's MAX or HOT line when the engine is hot, and lower when it's cold.

Yes. Draining out the coolant and refilling the system removes dirt and rust particles that can clog up the cooling system and cause problems in winter and summer.

Why do I have to do this?

Because it is operating in a hot, hostile environment, coolant will break down over time. Most importantly, the coolant's rust inhibitors get used up, leaving the small cooling passages in your engine and radiator vulnerable to corrosion. Even with these rust inhibitors, some corrosion will inevitably take place, contaminating the coolant with debris.

What happens if I don't do this?

If the rust inhibitors stop working, the cooling system will rust from the inside out. The biggest source of rust in a car's cooling system is the engine block.

In time, these bits of rust will also clog the tiny passages within the radiator and heater, causing your engine to overheat. When an engine overheats, the result is a bonus yacht payment to your mechanic that someone else should be making.

Is there any maintenance required between intervals?

Check your coolant level periodically. Your owner's manual will have a recommended interval in which to check the coolant level.

If you check your coolant level when the engine is cold, the coolant should be at or above the "minimum" or "fill" line on the transparent refill container. If you check your coolant level when the engine is hot, the coolant should be at or just below the "max" line.

Disappearance of coolant could be caused by either an external or internal leak, the latter being more expensive. Either one should be addressed quickly, since running low or out of coolant can lead to catastrophic engine failure and many boat payments to your mechanic.

If you live where the temperature dips below freezing, we suggest that you ask your mechanic to check the concentration of the coolant. Coolant that's diluted or weak can freeze when the temperature drops below 32 degrees Fahrenheit.

Check your owner's manual to see if your car uses "long-life" coolant. For the first 100,000 miles, it is necessary to check the coolant level simply to be sure you're not leaking or burning coolant.

Car Talk Tip: Antifreeze has a sweet aroma and taste, which pets find particularly appealing. As little as a half teaspoon of the stuff can kill an average-size cat, and eight ounces will do in a 75-pound dog. There's no substance that you can add to antifreeze to make it less appealing to animals, but antifreeze made with propylene glycol instead of the usual ethylene glycol is about a third as toxic. Propylene glycol is sold under the brand names Sierra, Prestone Low Tox and Texaco PG.