What does this sensor on Toyota thermostat housing do?

"This device is a heat-sensitive switch that remains closed until the engine's coolant reaches a certain temperature. The PVS screws into the intake manifold, thermostat housing or engine so the heat- sensing element is in contact with the engine's coolant. Inside the switch is a wax plug that pushes a sliding plunger to uncover or block vacuum ports in the switch. As the engine heats up, the wax expands and pushes the plunger up until it uncovers or blocks the vacuum port. At this point, vacuum to the device that the switch controls is either applied or blocked. Severe engine overheating can damage the switch, making replacement necessary."

"brassplyer" wrote

According to Autozone's 89-90 Cressida diagram, your BVSV decides when the charcoal cannister is allowed to vent its vapors into the intake manifold.

or:

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My wife wishes I had one of those. I vent my vapors any time and anywhere I want.