Understanding Antifreeze

Antifreeze was developed to overcome the shortcomings of water as heat transfer fluid. If the engine coolant gets too hot, it might boil while inside the engine, causing voids (pockets of steam), leading to localised hot spots and the catastrophic failure of the engine. If plain water were to be used as an engine coolant, it would promote galvanic corrosion. Proper engine coolant and a pressurised coolant system can help obviate the problems which make plain water incompatible with automotive engines. With proper antifreeze, a wide temperature range can be tolerated by the engine coolant, such as ?37°C to +129°C for 50% (by volume) propylene glycol diluted with water and a pressurised coolant system.

Early engine coolant antifreeze was methanol alcohol, still used in windscreen washer fluid. As radiator caps were vented, not sealed, the methanol was lost to evaporation, requiring frequent replenishment to avoid freezing of the coolant. Methanol also accelerates corrosion of the metals, especially aluminium, used in the engine and cooling systems. Ethylene glycol was developed, and soon replaced methanol as an engine cooling system antifreeze. It has a very low volatility compared to methanol and to water.

Antifreeze is an additive which lowers the freezing point of a water-based liquid. An antifreeze mixture is used to achieve freezing point depression for cold environments and also achieves a higher boiling point to reach higher coolant temperatures. Freezing and boiling points depend on the concentration of the dissolved antifreeze.

The purpose of antifreeze is to prevent a rigid enclosure such as a radiator from bursting due to expansion when water freezes. Careful selection of an antifreeze can enable a wide temperature range in which the mixture remains in the liquid phase, which is critical to efficient heat transfer and the proper functioning of heat exchangers.

Automotive and internal combustion engine use

Most automotive engines are water cooled, although the water is actually antifreeze/water mixture and not plain water. Corrosion inhibitors are added to the antifreeze/water mixture in an automotive context, to help protect vehicles radiators, which often contain a range of electrochemically incompatible metals. Water pump seal lubricant may also be added. Most modern Silicone compound materials are engineered to resists this corrosion, however some new advanced coolants on the market are formulated differently, and contain more aggressive chemicals or inhibitor which may not always be compatible with silicones. Traditionally, there were two major corrosion inhibitors used in vehicles: silicates and phosphates.

Some vehicles traditionally use both silicates and phosphates, whilst some makes contain silicates and other inhibitors, but no phosphates. Some Japanese makes traditionally use phosphates and other inhibitors, but no silicates.

Organic Acid Technology  & Silicone Hoses

Certain cars are built with organic acid technology (OAT) antifreeze, or with a hybrid organic acid technology (HOAT) formulation, which claimed to have an extended service life of five years or 240,000 km (150,000 mi).

Some OAT grades cause controversy. Litigations have linked it with intake manifold gasket and other damages in some cars, one of the anti-corrosion components presented as sodium or Potassium 2-ethylhaxanoate and ethylhexanoic acid is incompatible with nylon and Silicone Rubber.

Another culprit appears to be operating vehicles for long periods of time with low coolant levels. The low coolant is caused by pressure caps that fail in the open position. This exposes hot engine components to air and vapors, causing corrosion and contamination of the coolant with iron oxide particles, which in turn can aggravate the pressure cap problem as contamination holds the caps open permanently.

Some new extended life coolants use OAT with silicate but without the 2-EHA. Some added phosphates provide protection while the OAT builds up. Some specifically excludes 2-EHA from their formulas.

Typically OAT antifreeze contains an orange dye to differentiate it from the conventional glycol-based coolants (green or yellow). Some of the newer OAT coolants claim to be compatible with all types of OAT and glycol-based coolants; these are typically green or yellow in colour.

VIPER PERFORMANCE OAT Coolant grade SILICONE HOSES

Viper Performance silicone hoses can supply a OAT resistant grade silicone hose which also withstands much higher temperatures than conventional coolant hoses. The OAT grade hoses will operate in the range of 150°C up to +230°C, making this suitable for use in higher, under bonnet temperatures.

For Identification purposes OAT grade hoses are manufactured in colour green. This build and material is only made by special order and costs more than normal silicone hoses.



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