M51 series engine thermostat
4 - thermostat housing;
5 — a bolt for removal of air;
6 - thermostat;
7 - sealing ring;
10 — a bolt with a six-sided head.
M52 series engine thermostat
4 - thermostat housing;
5 - thermostat;
6 - sealing ring;
7 - flat gasket;
8 - bolt with M6 thread;
9 - bolt with M8 thread.
The thermostat, when the engine warms up, opens a large circle of coolant circulation. If the thermostat remains closed due to a fault, the engine will be too hot. This can be determined by the fact that the temperature indicator needle is in the red area, and the radiator remains cold. A faulty thermostat may also remain open after the fluid in the engine has cooled. This can be determined by the fact that the engine does not reach its operating temperature or the temperature gauge needle rises more slowly than before, or the heater does not work efficiently during the cold season.
Attention: When the engine becomes hot after a short trip, this may be due to clogging of the radiator with lime deposits.
Withdrawal
Remove the fan.
Drain some coolant and collect it.
Remove the hose from the thermostat housing (from the front side of the cylinder block), for which loosen the clamp.
Loosen the bolts and remove the engine lifting eye. Release the wire sheath from the clamps and remove it.
Loosen the screws and remove the thermostat housing cover.
Mark the position of the thermostat and remove it.
Examination
Heat the thermostat in a container of water. In this case, the thermostat should not touch the walls of the container. The temperature must be measured with a suitable thermometer.
At about 88°C, the thermostat valve will start to open. The opening temperature of the thermostat is also indicated on its surface.
Check if the thermostat expands and closes again, and if the opening temperature corresponds to the value indicated on it.
Attention: The travel of the thermostat valve must be 8.0 mm.
Installation
Clean the sealing surfaces of the body and cover.
Series M52: Insert the thermostat into the cylinder head with the arrow pointing up.
Series M51 and M30: insert the thermostat with the bleeder valve pointing upwards. It is located with the cover installed in its recess.
Lightly coat the new O-ring with glycerine and insert the O-ring.
Series 52: Always replace the flat paper spacer.
Install the thermostat housing and evenly tighten its fastening bolts to 10 Nm.
Caution: Do not overtighten the bolts. On a 6-cylinder petrol engine, don't forget the engine lifting eye. Tighten its mounting bolts.
Series M70: insert the thermostat so that the bleed valve (1) was directed upward. Install new seal (2).
Secure the wire sheath with clips. Install the fan and its cover. Fill the system with coolant and bleed air from the cooling system. Warm up the engine until the viscous coupling turns on the fan. Check if the radiator is warm at the bottom and if there are any leaks on the thermostat housing. If there are leaks, tighten the bolts a little.
M30 engine thermostat
1 - hose;
2 - bracket;
3 - collar;
4 - hex bolt M6x25/M6x35/M6x70;
5 - spring washer;
6 - cover;
7 — a bolt of release of air;
8 - gasket;
9 - thermostat;
10 - sealing ring.
Elements of the M30 engine thermostat housing
1 - thermostat housing;
2 - gasket;
3 - sealing ring;
4 - thermal valve;
5 - vacuum hose, black;
6 - thermal switch;
7 - temperature sensor of the injection device;
8 - coolant temperature indicator sensor;
9 - thermal switch;
10 - threaded plug;
11 - copper sealing ring;
12 - hex nut;
13 - spring washer;
14 - hose clamp;
15, 16 - hose.