Coolant Temperature Override (CTO)
This system supplies carburetor ported vacuum or manifold vacuum to distributor vacuum advance, depending upon coolant temperature. Three types of CTO switches are used: a single-function switch for models with standard cooling, a single-function switch for models with heavy duty cooling and a dual-function switch. The CTO switch is threaded into the left rear of block on 6-cylinder models, and into the thermostat housing on V8 models. On some models a NLVR valve is used along with a CTO switch.