Coolant Temperature Override Switch

Fig 36 EGR CTO Switches, 1973-81:

Fig 37 EGR CTO Switches, 1982:

This switch is located at the coolant passage of the intake manifold (adjacent to oil filler tube) on a V8 engine or at the left side of the engine block (formerly the drain plug location) on a six cylinder engine.

On 4-121 engines, the switch is located in the coolant passage on the bottom of the intake manifold. On 4-151 engines, the switch is located in the coolant passage at the right rear of the cylinder head.

When coolant temperature is below the specified rating of the CTO switch, there is no vacuum signal to the EGR system. The switch for the 4-151 engine, opens at 100° F. On all other engines, opening temperature is 85° F for switch with white body, 115° F for switch with black body or paint dab and 160° F for switch with yellow body or paint dab.