Vernet TH686690J Thermostat – Volvo

The engine thermostat in your Volvo is vital for maintaining an optimal engine operating temperature. It is a valve that closes when the engine temperature is low, allowing coolant to circulate inside the engine until it warms up. It opens when the engine temperature exceeds its optimal temperature to allow coolant to enter the radiator, where it is cooled before returning to the engine. It operates by having a wax pellet formulated to melt at a specific temperature that expands when melted to open the valve and contracts when closed, allowing the valve to close.

Thermostats fail when the valve gets stuck either open or closed. When a thermostat is stuck closed, it does not allow coolant to flow freely from the engine to the radiator, causing the engine to overheat. If the thermostat sticks open, coolant continuously flows freely through the radiator preventing the engine from adequately heating up. The thermostat can also fail by only partially opening or not fully closing, making the engine unable to operate in its optimal temperature range, causing it to consume excessive fuel and produce excessive tailpipe emissions.

When the thermostat fails, you must replace it for the engine to run at peak efficiency. It is also recommended to replace the thermostat when any other part of the cooling system causes the engine to overheat, as the excessive heat could have damaged the thermostat.

Although nearly every engine thermostat functions the same, differing designs and placements of thermostats vary in replacement times and difficulty. When replacing thermostats, it is vital to bleed out any air that may be trapped in the cooling system, as it prevents the cooling system from properly pressurizing and can prevent coolant from reaching parts of the engine.

Volvo Thermostats.