How Often Should You Change Your Antifreeze/Coolant?
I was speaking with our Shop Foreman, Robert Isbell, the other day as he was working on a customer vehicle. I Inquired as to what was wrong with the vehicle. He stated that the thermostat stuck and as a result the vehicle overheated and had to be towed in. He further explained that the thermostat is a mechanism that opens and closes many times during the time the engine is running to maintain proper engine temperature. If it sticks closed it prevents the coolant from circulating through the engine, it overheats and suddenly your stranded, worse, you might do major engine damage. I asked why the thermostat would stick. He stated that when the engine coolant is not maintained properly, it becomes dirty and sticky and deposits form on the plunger of the thermostat and as a result, one day it sticks closed and doesn’t open again. Result? Stranded. Don’t know about you, but just the sound of the word ‘stranded’, is bothersome. So I thought this might be a good subject to begin our monthly ‘Service Tips’ with.
For “ordinary” antifreeze, Honda recommends coolant changes every two years or 30,000 miles. On newer Honda’s ( 2006 and Up) the on-baord diagnostics will let you know via the “Maintenance Minder”. Some say it’s not a bad idea to change the coolant every year for maximum corrosion protection.
CAUTION: New long life coolants provide extended life only when used in a clean system mixed with water. If mixed with ordinary antifreeze and/or old coolant in a system, the corrosion protection is reduced to that of normal antifreeze (2 to 3 years and 30,000 miles).
The life of the antifreeze depends on it’s ability to inhibit corrosion. Silicates, phosphates and/or borates are used as corrosion inhibitors to keep the solution alkaline. As long as the antifreeze remains so, corrosion is held in check and there’s no need to change the coolant. But as the corrosion inhibiting chemicals are used up over time, electrolytic corrosion starts to eat away at the metal inside the engine and radiator. Aluminum is especially vulnerable to corrosion and can turn to Swiss cheese rather quickly when conditions are right. Solder bloom can also form in copper\brass radiators causing leaks and restrictions. So changing the coolant periodically as preventative maintenance is a good way to prevent costly repairs.
The basic idea is to change the coolant before the corrosion inhibitors reach dangerously low levels. Following Honda’s change recommendations is usually good enough to keep corrosion in check, but it may not always be the case. That’s why more frequent changes may be recommended to minimize the risk of corrosion in bimetal engines and aluminum radiators.
Checking The Antifreeze
One way to find out if it’s time to change the antifreeze is to test it, and this can also be performed for you when you bring your vehicle in to Honda of Oakland for it’s regular maintenance. Several suppliers make special antifreeze test strips that react to the pH (alkalinity) of the coolant and change color. If the test strip indicates a marginal or bad condition, the coolant should be changed.
Changing The Coolant
Reverse flushing is the best way to change the coolant because draining alone can leave as much as 30 to 50% of the old coolant in the engine block. Reverse flushing also helps dislodge deposits and scale which can interfere with good heat transfer.
The concentration of antifreeze in the coolant also needs to be checked prior to the onset of cold weather. A 50/50 mixture of antifreeze and water is recommended and will protect against freezing down to -34 degrees F and boil over protection to 263 degrees F.
For maximum protection, up to a 70% mixture of antifreeze can be used for freezing protection to -84 degrees F.