According to this article,
5 things to know about your car radiator and how to keep it cool, engine coolant(antifreeze) is necessary to keep a vehicle's engine from overheating.
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Snipped from article:
"Coolant, a mixture of antifreeze (ethylene glycol) and water is a fluid pumped around the engine and kept cool with the help of the radiator. The purpose of this antifreeze is to keep the water in the radiator from freezing in cold temperatures and, more relevant to the UAE, boiling over in the warmer climates.
A low coolant level in the radiator is one of the major reasons for overheating in vehicles."
ETA: I'm not a resident nor have I visited DR, but seems like coolant would be sold in auto parts/supply stores, large retailers, and possibly even convenience/grocery stores.