Check the condition and connections of all cooling system hoses and heater hoses. Replace any swollen or deteriorated hoses. The coolant level should be filled between F and L marks on the side of the coolant reservoir when the engine is cool. If the coolant level is low, add enough distilled (deionized) water.

The high-pressure cooling system has a reservoir filled with year-round antifreeze coolant. The reservoir is filled at the factory. Check the antifreeze protection and coolant level at least once a year, at the beginning of the winter season, and before traveling to a colder climate. Checking the coolant level; Changing the coolant

When to Get Service With Your Hyundai Engine Coolant. Coolant is thinner than motor oil yet thicker than water. If you notice a sludgy appearance when you check your Hyundai coolant level, schedule service with our team ASAP. Your engine might have an internal gasket leak.

Fifth generation (MD/UD; 2011–2016) / Hyundai Elantra MD 2010-2015 Owners manual / Maintenance / Engine coolant / Checking the coolant level / Recommended engine coolant When adding coolant, use only deionized water or soft water for your vehicle and never mix hard water in the coolant filled at the factory.

If vehicle came with green coolant installed, I'd recommend using the following; Zerex Asian Vehicle Green Antifreeze/Coolant Zerex from Valvoline is the #1 selling OEM-approved coolant brand.