The 2018 Kia Optima uses an ethylene glycol-based long-life coolant that meets Kia/Hyundai specifications. The safest choice is Kia Genuine Long-Life Coolant or an aftermarket coolant explicitly approved for Kia/Hyundai HOAT systems. Do not mix different coolant types or use products not labeled for this vehicle.
Understanding the coolant specification
The Optima’s cooling system relies on a corrosion-inhibitor package designed for aluminum engines and mixed metals. Using the correct coolant helps prevent overheating, corrosion, and leaks. Kia’s guidelines commonly call for a long-life coolant that uses Hybrid Organic Acid Technology (HOAT) with a glycol base.
What to buy
To keep maintenance straightforward, choose coolant that is labeled as meeting Kia/Hyundai long-life HOAT specifications. The following options are typically acceptable:
- Kia Genuine Long-Life Coolant (pre-diluted ethylene glycol-based HOAT)
- Hyundai/Kia-approved aftermarket coolants labeled to meet the Kia/Hyundai long-life HOAT specification
- Any HOAT coolant that explicitly states compatibility with Kia/Hyundai long-life coolant
Important: Do not use coolants that are OAT-only or Dex-Cool-style unless the product documentation confirms compatibility with Kia/Hyundai engines.
Maintenance and usage tips
Always ensure the engine is cool before opening the cooling system. If using a concentrate, prepare a 50/50 mix with distilled water unless the product is pre-mixed. Follow the product label and the owner’s manual for exact dilution and refilling procedures, and have the cooling system pressure-tested for leaks as part of routine service.
Summary
For a 2018 Kia Optima, use a ethylene glycol-based long-life coolant that meets Kia/Hyundai HOAT specifications. Opt for Kia Genuine Long-Life Coolant or an approved aftermarket equivalent, and avoid mixing incompatible formulas. When in doubt, consult the owner's manual or a Kia dealership for the exact specification and approved product list.