Spark Coolant Temperature Override (CTO) System
This system alternates distributor vacuum advance vacuum source between carburetor ported vacuum or delayed manifold vacuum and normal manifold vacuum, depending upon coolant temperature. Two types of CTO switch are used: a single-function switch for models with standard cooling systems, and a single-function switch for heavy duty cooling systems.
CTO switch is threaded into left rear of block on 6-cylinder engines, and into thermostat housing on 4-cylinder and V8 engines. On some models, this system is used in conjunction with NLVR valve.