Coolant Check
The vehicle must be on a level surface when checking the engine coolant level.

Check that coolant is visible in the coolant recovery reservoir. If the coolant inside the coolant recovery reservoir is boiling, do nothing more until it cools. If coolant is visible but the coolant level marks are not visible, add a 50/50 mixture of clean drinkable water and DEX-COOL coolant to the coolant recovery reservoir up to the upper edge of the middle of the reservoir, but make sure the cooling system is cold before doing so. See Engine Overheating.
The coolant recovery reservoir is located in the engine compartment on the driver's side of the vehicle. See Engine Compartment Overview.
Test yourself
A quick GMC Terrain quiz: every answer comes with an explanation and a link to the manual page.