Thermostat
signs
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Cause/Consequences
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A. The temperature rises slowly, operating temperature is reached later, insufficient heating effect | Thermostat valve plate locked in position «open» (German «Offen») (e.g. due to sediment); fluid flow to the radiator open. The engine has been running cold for too long. But for for a short period of time it does no harm. Despite this, quickly change the thermostat. |
B. The arrow of the temperature indicator is deflected to the right until limit, despite the correct coolant level, the control indicator flashes coolant light. Radiator and bottom hose to radiator cold. | Thermostat valve plate locked in position «closed» (German «Geschlossen») (e.g. due to a defective or leaky box thermostat). Under no circumstances continue the trip, otherwise serious thermal damage to the engine! Replace thermostat immediately. |
Tip: If the engine boils on the road due to a defective thermostat, only towing or completely dismantling the thermostat on site will help. If you decide to dismantle the thermostat, you must first wait until the temperature of the coolant drops.
Four-cylinder engine: showing the inside of the water pump and thermostat (cutaway). The impeller is clearly visible (1) water pump. There is a thermostat nearby (2).
With a six-cylinder engine, the thermostat housing (arrow) located on the right front of the engine block.
The figure shows the installation position of the thermostat for a four-cylinder engine. Air valve (arrow) should be turned up.
Removing the thermostat
A stuck thermostat is very difficult to dismantle on the road. It is located quite far below, so you need to drain almost all the coolant. In addition, with a hot engine, it will take quite a long time before you can start working without fear of burning your hands. When installing a new thermostat, the O-ring on the thermostat and water pump housings must also be replaced.
1. For all models: Drain the coolant completely.
2. Four-cylinder engine: remove the lower lining of the engine compartment (chapter Body parts).
3. Unscrew the hose at the bottom of the water pump housing (what has already been done to drain the coolant).
4. Unscrew the two screws at the bottom of the thermostat housing cover.
5. Remove cover and thermostat.
6. Six-cylinder engine: remove the V-belt, remove the tensioner.
7. Remove the toothed belt cover (chapter Engines). The timing belt itself remains in place.
8. Remove the coolant supply hose to the radiator at the bottom of the hose fitting on the thermostat housing.
9. Unscrew two bolts on a cover of the case of the thermostat.
10. Carefully lift the toothed belt over the jumper of the thermostat housing, remove the housing.
11. Remove the thermostat.
12. For all models: when installing a new thermostat, its small sealing plate must be turned towards the engine.
13. Six-cylinder engine only: air valve in thermostat outer ring must face up.
14. Replace O-ring.
15. Tighten the bolts on the thermostat housing and the water pump with a tightening torque of 10 Nm.
Thermostat check
Using the built-in thermometer, you can check whether the thermostat opens at a given temperature.
Start of opening
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End of opening
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Min. opening stroke
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About 87°C
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About 102°C
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About 8 min
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1. Remove the thermostat.
2. Hang the thermostat in a container of water and heat the water.
3. Check if the valve disc rises in the seat when the temperature reaches 87°C.
4. With this check, the end of the opening may not be completely reached (as you know, water in an open container boils at about 100°C), but you can still see if the thermostat opens more.
5. But the total length of the opening stroke is almost reached. But what is visible is already enough to identify a defective thermostat.
6. At the slightest doubt in serviceability of the thermostat replace it.
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