Cooling System: Description and Operation

Coolant circuit (2-phase)





A From coolant thermostat to radiator
B From radiator to coolant pump
C Bypass duct
D Coolant flow from expansion tank to radiator
E Vent hose upper coolant box to expansion tank
F Vent hose inlet connection (thermostat housing) to vent hose between upper coolant box and expansion tank
G Overflow hose
H Heating water feed from cylinder head (intake manifold left) to heat exchanger
J Heating water return duct in Cylinder crankcase right
K Heat exchanger
L Expansion tank

1 Main valve coolant thermostat
2 Bypass valve coolant thermostat
3 Control bore
4 Pin





NOTE: On the engines 116.960 and 116.961 national versions (AUS) (J) (S) (USA) 1981, the vent line (F) is installed with effect from August 1981.

Production Breakpoint: August 1981:

Instead of vent hose (arrow) by way of which the cooling system has been continuously and automatically vented during filling operation and also during operation of engine, the vent screw (7) has been used up to August 1981. This screw must be opened for venting when filling the cooling system. When using this vent screw, no automatic, continuous venting of cooling system will occur.

Operation

NOTE: Independent of coolant temperature or position of coolant thermostat, a small quantity of coolant will always flow through the control bore (3) to the coolant pump. The pin (4), connected to the wax element by means of a web, will move up and down with the stroke of the wax element in the control bore to keep the bore free of contamination.

Warming-up period (phase 1, coolant temperature up to approx. 84 °C)
The main valve (1) is closed up to a coolant temperature of approx. 84 °C and interrupts the coolant flow towards the radiator (A) and through the bypass duct (C). Only a small quantity of coolant will flow through the control bore (3) to the coolant pump during the warming-up period. This design provides faster heating of the engine during the warming-up period, especially in the combustion chamber region in the cylinder head.

Part-load operation (phase 2, coolant temperature approx. 84 °C to max. 99 °C)





In the part-load range (engine at operating temperature) the main valve (1) and the bypass valve (2) are more or less open depending on the engine load and ambient temperatures. The coolant flows as a function of coolant thermostat position both through radiator (A and B) as well as bypass duct (C) to the coolant pump.

Full load operation - High ambient temperatures (coolant temperatures above 99 °C)





Under heavy engine load and/or high ambient temperatures the main valve (1) is fully open at a coolant temperature of approx. 99 ° C, and the bypass valve (2) is closed. The entire coolant will now flow through the radiator to coolant pump (A and B). It is there- fore wrong to remove the coolant thermostat to obtain an "improved" engine cooling.