Engine Coolant:
What, Why, & When
What?
Your engine's coolant or antifreeze is primarily ethylene glycol (a clear, colorless, odorless, viscous liquid with a sweet taste which, unlike the glycerine or alcohols it is based on is quite toxic when consumed), water, and corrosion inhibitors. The ethylene glycol prevents freezing of the coolant in cold weather and, by raising the boiling point above that of water, it prevents overheating in warm weather. The corrosion inhibitor stops the dissimilar metals used in modern engines from corroding into oblivion.
Why?
The thing most people understand about antifreeze is that it keeps your engine from overheating and freezing up. Though that's important, just as important is the corrosion inhibiting properties of antifreeze and most people have no idea what corrosion does to an engine. We see far more damage and costly repairs due to corrosion than freeze ups and overheating. By far. When coolant loses it ability to prevent corrosion (after about two to five years) it actually causes corrosion by becoming acidic. Then electrolysis sets up between the dissimilar metals and, just like a battery, one of the metals starts to corrode. It can be the engine block, cylinder head, head gasket, or any number of other parts. It's usually the head gasket. A new car can suffer a corrosion-related engine failure in 6 to 10 years if the coolant is never changed. This frequently-overlooked maintenance is both easy to do and inexpensive.
When?
Every two years. It costs about $50.00 on most cars. Also at around 90,000 miles the thermostat should be replaced.
Starting in 2003, Honda and Toyota went to 90,000 to 120,000 miles before coolant changes by using a "super long-life coolant" blend. We retrofit all Hondas to the long-life coolant. On cars with this more stable coolant we recommend changing it every 5 years. Other Japanese cars are 2 years or 30,000 miles. Individual European models are different. Check with us about your car, we have the data.