The burst point of an antifreeze is the temperature
at which a sealed copper pipe filled with the
undiluted product will burst. Burst points are a
standard created by the plumbing industry in the
1930s to indicate the relative strength of antifreeze.
They have since become synonymous with the
name of antifreeze products used for winter storage.
Burst points help consumers choose the proper
product based on the lowest expected temperatures
for their specific area.
A freeze point is the temperature at which ice
crystals begin to form in the undiluted product.
Freeze points are the measurements given when
using refractometers and hydrometers. Note: most
refractometers provide readings on both a PG and
an EG scale, so it is important to use the PG reading
when testing this product. Hydrometers are either
made to provide PG or EG readings. It is critical to
test this product with a hydrometer specifically designed to provide PG readings. Most hydrometers
are purchased at auto supply stores and are
designed for use with EG, so they cannot be used to
test PG antifreeze. Keep in mind that it is normal to
see readings that may vary by several degrees from
the product's stated freeze point based on ambient
temperature or the age of the product. For example,
the freeze point of the -50°F product is +12°F, but it
is not unusual to see readings in a range of +12°F to
+16°F. Shake PG antifreeze well before testing as
the heavier PG component may have settled toward
Because the stored engine or water system is not in
use, preventing ice crystals is not necessary, and to
do so would require the use of a more expensive
product with a higher PG content. As an example, the
-50°F antifreeze has a freeze point of +12°F while the
-100°F antifreeze has a freeze point of -60°F.
However, as the temperature drops the solution
begins to solidify and expand, it puts pressure on
pipes that can lead to damage. This is why it is
important to select an antifreeze that will provide
burst protection appropriate for a specific region's
lowest anticipated temperatures. Products providing
lower burst point temperatures contain higher
concentrations of PG and are thus more expensive,
but they will provide the protection needed in the
event of extreme weather.