1993 Honda Civic Owner's Manual - Page 116

Cooling System cooling system. They may not be compatible with the coolant or engine components. Replacing Engine Coolant The cooling system should be completely drained and refilled with new coolant according to the time and mileage recommendations in the maintenance schedule. Only use recommended antifreeze. Draining the coolant requires access to the underside of the car. Unless you have the tools and knowledge, you should have this maintenance done by a skilled mechanic. RESERVE TANK 2. Turn the radiator cap counterclockwise, without pressing down on it, until it stops. This relieves any pressure remaining in the cooling system. 3. Remove the radiator cap by pushing down and turning counterclockwise. 4. The coolant level should be up to the base of the filler neck. Add coolant if it is low. 5. Put the radiator cap back on. Tighten it fully. 6. Pour coolant into the reserve tank. Fill it to halfway between the MAX and MIN marks. Put the cap back on the reserve tank. Do not add any rust inhibitors or other additives to your car's Maintenance