THERMO Valves
Thermo valves are used to sense engine coolant temperature and prevents EGR operation when below preset value. When engine warms up, thermo valve opens to allow vacuum passage to EGR valve, which then determines EGR flow. Below about 131°F (55°C), thermo valve is open, causing vacuum to be vented, thus not reaching EGR valve. Above about 131°F (55°C), thermo valve closes and normal EGR operation is accomplished.