Spark Coolant Temperature Override (CTO) System

This system operates during cold engine warm-up to improve driveability. The CTO switch is threaded into bottom of intake manifold on 4-cylinder engines, into left rear of block on 6-cylinder engines or thermostat housing on V8 engines. The CTO switch responds to coolant temperature to allow either manifold vacuum or carburetor ported vacuum to the distributor. On some models, this switch is used alone, on others it is used in conjunction with the Transmission Controlled Spark (TCS) system.

Fig 1: Spark Coolant Temperature Override Switch

Courtesy of AMERICAN MOTORS/RENAULT CORP.