The primary drain point is the radiator drain petcock. This is usually a valve located at the bottom of the radiator. Open this to drain the majority of the coolant.
To get more coolant out of the engine block itself, you'll need to loosen the lower radiator hose. This allows coolant to drain from the block as well. Be aware that this will result in a larger mess. Have a suitable drain pan and possibly some towels ready.
Important Considerations:
* Always let the engine cool completely before attempting to drain the coolant. Hot coolant can cause serious burns.
* Protect the environment by properly disposing of the used coolant. Auto parts stores often accept used coolant for recycling.
* Consult a repair manual specific to your 1988 Mercury Sable. A Haynes or Chilton manual will show diagrams and provide detailed instructions. This will give you precise locations and steps.
While some older vehicles *did* have a block drain plug, it's not a common feature on the 1988 Mercury Sable. Draining from the radiator and lower hose is the standard procedure.
