1986/02/01 Caterpillar

There has been an increasing number of reported field problems related to inhibitor dropout from high silicate commercial antifreeze which involve radiator and cooling system plugging, increased deposits resulting in overheating and water pump seal leakage. Commercial antifreeze formulations in the United States have changed to accommodate the corrosion requirements of aluminum engine components used in automotive gasoline engines. This change involved increasing the concentration of silicates, an effective means to protect aluminum parts. When these antifreezes are mixed with water, especially hard water, and then added with supplemental corrosion inhibitors, several situations can and do occur:

... The total solids in the coolant solution increase to cause an insoluble condition for unstable chemicals, such as silicates and phosphates. These solids can build up in latent areas and cause plugging or loss of heat transfer.

... A silica gel (polymerization of the silicate) can be formed. These gel formations can result in loss of cooling or heating in radiators, aftercoolers and cab heater cores by coating or plugging tubes. It usually deposits in the cooler section of the cooling system, such as radiator bottom tank, etc.

... A large quantity of precipitants combined with the gel in the cooling system can cause wear leading to water pump seal failures.

Some steps can be taken to minimize the occurrence of silicate dropouts.

* Use antifreeze containing low silicates.

Most commercially available antifreezes are formulated for gasoline engine applications and, therefore, will have high silicate content. A specification that limits the amount of silicate content is the GM-6038. This product is not readily available at this time, but many antifreeze manufacturers are making it available because of customer requests. Use of antifreeze meeting GM-6038 may not necessarily prevent the problem but will certainly reduce the severity.

* Use good quality water.

The tendency of silicates to precipitate out of solution increases with increasing water hardness. Hard water, or water with high levels of calcium and magnesium ions, encourages the formation of the gel especially after a number of heating and cooling cycles.

Caterpillar prefers the use of distilled water or deionized water to reduce the potential and the severity of silicate dropouts. The minimum acceptable water that should be used in a coolant mixture of 50% antifreeze and 50% water must have the characteristics shown in Chart A from "Know Your Cooling System", SEBD0518-02. Using water that meets this requirement may not prevent silicate dropout totally but should minimize the rate to acceptable levels.

* Use lesser amounts of antifreeze.

The reason for the use of antifreeze or ethylene glycol is strictly for freeze protection. In many areas of the world where freeze protection is not needed (in the tropics), the use of plain water treated with a coolant conditioner inhibitor package is sufficient to protect the engine against corrosion and pitting. Therefore, in those areas where there is no need for protection down to -37°C (-34°F) use of a 50% antifreeze is not essential. Chart B provides some guidelines for the amount of antifreeze and freeze protection temperatures.