You MUST consult your owner's manual. This is the definitive source for the correct spark plug gap for your specific vehicle.
Failing that, you can find the information:
* Online: Search for "[Your Town Car's Engine Size] spark plug gap" (e.g., "4.6L Lincoln Town Car spark plug gap"). Several reputable automotive websites will provide this information. Be sure to cross-reference the information with multiple sources.
* Auto Parts Store: Take your vehicle's information (VIN number is best) to an auto parts store. They can look up the correct specification for your car.
Using an incorrect spark plug gap can lead to poor engine performance, misfires, and damage to your engine components. Always use the recommended gap.