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According to the DEX-COOL manufacturer, "mixing a 'green' [non-OAT] coolant with DEX-COOL reduces the batch's change interval to 2 years or 30,000 miles, but will otherwise cause no damage to the engine".
[26] DEX-COOL antifreeze uses two inhibitors:
sebacate and 2-EHA (
2-ethylhexanoic acid), the latter which works well with the
hard water found in the United States, but is a
plasticizer that can cause gaskets to leak.
[18]
According to internal GM documents,
[26] the ultimate 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. (The new caps and recovery bottles were introduced at the same time as DEX-COOL). 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.
[26]
Honda and Toyota's new extended life coolant use OAT with sebacate, but without the 2-EHA. Some added phosphates provide protection while the OAT builds up.
[18] Honda 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), though some OAT products may contain a red or mauve dye. 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 color.
[17]