The temperature at which the main thermostat valve opens is 85°C.
Full opening temperature of the main valve 105°C.
The piston stroke of the main valve is at least 7 mm.
The Bosch or AEG two-speed electric fan is switched on and off by a sensor mounted on the left radiator tank.
The sensor for turning on the electric fan ensures the operation of the fan with low and high speeds. The sensor contact closing temperature to ensure a low fan speed is 92-97°C, a large one is 99-105°C, the sensor contact opening temperature is 84-91°C and 91-98°C, respectively.
On cars manufactured in 1995-96. with air conditioning, a three-speed electric fan is used.
Depending on the configuration, two sensors for turning on the electric fan are installed, one of which is located on the radiator tank and turns on the electric fan at the first two speeds, and the other is installed on the coolant outlet hose from the cylinder head on the left.
Fan motor start temperature:
- main sensor: at the 1st speed 92-97°С; at the 2nd speed 99-105°С;
- additional sensor 110-115°С.
Fan motor shutdown temperature:
- main sensor: at the 1st speed 84-91°C; at the 2nd speed 88-91°С;
- additional sensor 105-110°С.
To change the coolant, fully open the interior heating valve. Remove the expansion tank cap. Disconnect the radiator inlet hose from the thermostat housing (pic. 2-152) and drain the coolant.
![](https://www.vwmanual.ru/img/passat/1423.jpg)
Attach the radiator inlet hose to the thermostat housing and tighten the hose clamp. Pour coolant into the expansion tank up to the mark on the tank. Close the cap on the expansion tank, start the engine and let it run to remove air pockets from the cooling system. Check the fluid level in the expansion tank and top up if necessary.
To check the tightness of the cooling system, remove the plug of the expansion tank and install the VW 1274 test tool in its place. Using the hand pump of the tool, create an excess pressure of 1.0 kgf / cm2 in the cooling system2 and watch the pressure. If the system is sealed, the pressure generated must not decrease. To check the opening pressure of the safety valve in the expansion tank cap, install the expansion tank plug on the test tool.
By creating excess pressure with the help of a hand pump of the device, note the moment of opening the safety valve, which should occur at a pressure of 0.9-1.15 kgf / cm2.
![](https://www.vwmanual.ru/img/passat/1422-podp.jpg)
Pic. 2-151. Cooling system details:
1 - radiator;
2 - water pump;
3 - thermostat housing;
4 - expansion tank;
5 - heat exchanger;
6 - radiator casing;
7 - top cover;
8 - fan guide casing;
9 — electric fan mounting bracket;
10 — the directing casing of the fan on cars with the conditioner;
11 - electric fan;
12 - additional fan;
13 - additional fan drive belt.
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