1998 Buick Century Owner's Manual - Page 334

I MaintenanceSchedule I DATE 100,000 Miles (166 000 km) Inspect spark plug wires. An Emission Control Service. 0 Replace spark plugs. An Emission Control Service. 0 Change automatic transaxle fluid and filter if the vehicle is mainly driven under one or more of these conditions: - In heavy city traffic where the outside temperature regularly reaches 90°F (32 O C) or higher. - In hilly or mountainous terrain. - When doing frequent trailer towing. - Uses such as found in taxi, police or delivery service. Ifyou donot use your vehicle under any of these conditions,the fluid and filter donot require changing. I MILEAGE 150,000 Miles (240 000 km) 0 Drain, flush and refill cooling system (or every 60 months since last service, whichever occurs first). See "Engine Coolant'' inthe Index for what to use. Inspect hoses. Clean radiator, condenser, pressure cap and neck. Pressure test the cooling system and pressure cap. An Emission Control Service. 7-12