Question: How often should I change my antifreeze?
Answer: For "ordinary" antifreeze, the vehicle
manufacturers generally recommend coolant changes every two to
three years or 30,000 miles. Others say it's not a bad idea to
change the coolant every year for maximum corrosion protection
-- especially in vehicles that have aluminum heads, blocks or
radiators. But such recommendations may soon be obsolete. Several
antifreeze suppliers have just recently introduced "long
life" antifreeze formulations that claim to provide protection
for four years or 50,000 miles.
General Motors just introduced a new five year, 100,000 mile antifreeze
in its 1996 cars and light trucks. The new coolant is called
"Dex-Cool" and is dyed orange to distinguish it from
ordinary antifreeze (which is green).
CAUTION: These 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).
CORROSION INHIBITORS
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 copperrass
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 the OEM 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. 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 boilover 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.
CAUTION: Do not use more than 70% antifreeze, and never run straight
water in the cooling system because it offers no corrosion, freezing
or boilover protection.
