What type of antifreeze does my 2007 Hyundai Sonata use?

The 2007 Hyundai Sonata calls for the use of Peak OET engine coolant. It's recommended that You use a formulation that's designed specifically with Asian vehicles in mind -- both Peak and Prestone make great variants of this. You can expect to pay somewhere in the neighborhood of $18 to $25 for a gallon of the fluid. The most important thing in any engine is that You don't mix different types of antifreeze -- doing so can result in adverse reactions that create a jello-like substance. If You're unsure of what coolant is presently in Your engine (for example, if You purchased the vehicle preowned), You may want to consider doing a flush and fill, as opposed to a simple top off. This can save You from potentially serious engine damage.