Original submission by T Apr 4th 2007:
TVS (Thermal Vacuum Switch):
On 6 Cyl Engines, a 3 Port thermal Vacuum Switch is mounted in the top of the Thermostat Housing. On V8's it's mounted on the passenger side of the front of the Engine.
The purpose of the device is to increase the Engine Speed if the Engine overheats. It does this by providing full vacuum to the Distributor from the Inlet Manifold. The increase in engine speed accelerates the fan and water pump.
Below a coolant temperature of 104 degrees, the Distributor receives vacuum from a tap in the carburettor above the throttle. (Spark Ported Advance).
Above a coolant temperature of 104 degrees, the Distributor receives vacuum from a tap in the inlet manifold (below the throttle). (Vacuum Ported Advance).
The plastic tree in the manifold used to connect the vacuum hose have a tendancy to snap off when old. They can be replaced with brass fittings 1/4" BSP, 3/16" hose barb
The TVS plumbing causes full Inlet Manifold Vacuum to be directed to the Distributor above 104 degrees C. The purpose it to increase the idle speed which causes the fan and waterpump to spin faster increasing cooling. During an hot start, the switch can be in the Vacuum Ported position which will cause kicking back placing undue strain on the cranking system. Under normal conditions, Distributor Vacuum is supplied from above the Throttle which prevents the spark from being advanced until the Throttle is opened. Kickback starts don't occur when the Engine temperature is below 104 deg C.
Thermal Vacuum Switch Types:
Submitted by myehholden on Tue, 15/09/2009 - 07:23. *new There are two different thermal vacuum switches fitted to the blue and black motors on the passenger side of the head. You use one of each. They are coloured differently for identification. The RED one is Holden part number 460408 and the GREEN one is Holden number 3031386. Some of these green ones were also a tan colour. The green one was towards the front of the head and the red on towards the rear.
EGR Thermal Vacuum Switch:
The Exhaust Gas Recirculation Thermal Vacuum Switch has 2 ports, allows air to flow through it above 41 degrees letting Inlet Manifold Vacuum pull the EGR Valve Diaphragm and opening the EGR Valve. This is mounted on the Driver's Side of the front of the Engine on V8's and on the Manifold Side to the centre of the Head on 6 Cyl Engines.
EFE Thermal Vacuum Switch:
The Early Fuel Evaporation Thermal Vacuum Switch allows air to flow through it when cold but shuts off when the Engine reaches operating Temperature. The EFE TVS has 2 ports and activates the EFE Valve on the Inlet Manifold causing Exhaust Gas to heat the Floor of the Inlet Manifold. This is mounted on the Manifold side of the Head on 6 Cylinder Engines near the front of the Head.