Coolant Glossary

Antifreeze: Pure glycol (typically 95%) with an inhibitor package added. Antifreeze can not be used by

itself, it must be mixed with water before being put into the engine’s cooling system.

Azole: These chemicals provide copper and brass protection. The two most common are MBT

(Mercaptobenzothiazole) and TT (or TTZ) (Tolyltriazole).

Borate: a very soluble pH buffer used in premium antifreezes.

Coolant: Antifreeze mixed with water, or water mixed with an additive package for use in warm climates.

Conventional Coolant: Ethylene glycol that contains a corrosion inhibition package consisting of

inorganic inhibitors such as silicate, phosphate, nitrate, and azoles.

Fully Formulated antifreeze or coolant. A modern product that contains all of the necessary

inhibitors for both diesel and gasoline powered engines. (TMC RP-329 or TMC RP-330 specifications)

Ethylene Glycol: The most common base used in the manufacturing of antifreeze.

Nitrite: The primary inhibitor for wet sleeve liner pitting protection. It also protects against rust.

Nitrate: A corrosion inhibitor that provides solder and aluminum protection.

pH: A measure of the alkalinity of the coolant.

Reserve Alkalinity: A measurement of the number of milliliters of acid that is required to reduce the

pH of a coolant sample to 5.5. A quality control tool.

Silicate: The primary conventional inhibitor for aluminum. In heavy duty coolants, lower (less than 250

ppm) silicate concentrations are generally preferred.

Phosphate: An inexpensive pH buffer. Phosphate is used in some antifreeze brands. It is not permitted in

coolant used to protect Mercedes, BMW, Volkswagen MTU or Detroit Diesel engines.

Propylene Glycol: A less toxic, but more costly, alternative to Ethylene Glycol.