Antifreeze 101 Understanding Burst Points and Freeze Points - StarBrite

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 the bottom.

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.