Genuine Volvo S40 Thermostat

Volvo S40 Thermostat Parts and Q&A

• Thermostat
  271664
  Q: How does an aging thermostat affect water temperature regulation and what steps should be taken to assess and replace it on Volvo S40?

  A:

  As a thermostat ages, it can have a slower reaction time to changes in water temperature, which can cause it to get stuck in either the open or closed position, causing problems such as slow warm-up or rapid overheating. Before just concluding that it is the thermostat that has cause a cooling system problem it's important that you check the coolant level in the cooling system because if there is a leak or improper filling of the system there could be an air-lock. If the engine is slow to warm up, the thermostat may be stuck open, or it may be missing, with associated poor emissions and fuel economy results. If you have an engine that is running hot, but the Radiator top hose is not hot, the thermostat is probably stuck in the closed position, which means that coolant is not escaping to the radiator. On the other hand if the top hose is hot, coolant is flowing, indicating the thermostat is open. To test the thermostat's function, use a cold engine and measure the temperature at the radiator top hose as you monitor the coolant temperature gauge; the radiator hose should not be hot at first, but should heat up very quickly as the thermostat is opening. If the system does not function as expected, the thermostat should be taken off and tried. Make sure the engine is totally cold before you begin the removal process, which consists of emptying the cooling system and removing any necessary components such as the plastic engine cover and inlet manifold. For different engine models, the process involves disconnecting hoses, removing bolts and making sure to replace the thermostat with a new housing if faulty. Testing the thermostat includes heating water up to the temperature on the thermostat, making sure that the thermostat opens within two minutes, and making sure that the thermostat closes completely when the water cools. Refitting the thermostat involves reversing the removal procedure and replacing any gaskets or seals before topping up the cooling system.