Cooling System: Description and Operation
Coolant Circuit (3-phase)
A From the coolant pump to the crankcase
B From the cylinder head to the inlet pipe and bypass duct
C From the inlet pipe to the radiator
D From the radiator to the thermostat
E From the circulation pump to the coolant pump
F Radiator
G Vent hose from radiator to expansion tank
H Expansion tank (in bypass circuit) with coolant level indication
J Plug with pressure relief and vacuum valve
K Overflow hose
L Overflow tank (only with air conditioner/automatic climate control)
N From cylinder head/intake manifold to heat exchanger
P Heat exchanger
Q Mono valve
R Circulation pump electric
S Coolant filling hose
T Vent hose from inlet pipe
U Vent valve
1 Main valve coolant thermostat 80 °C
2 Bypass valve
Coolant pump
with laterally arranged thermostat 80 °C in the coolant feed from the radiator:
Operation
Coolant temperature up to approx. 80 °C
The main valve (1) is closed and the bypass valve (2) fully open. The feed (D) from the radiator is interrupted and the coolant flows via the bypass duct (B) directly via the coolant pump to the crankcase.
Coolant temperature of approx. 80° C up to max. 95 °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 temperature. The coolant is directed via both the radiator (C and D) and also the bypass duct as a function of the thermostat position.
Coolant temperature above 95 °C
The main valve (1) is fully open and the bypass valve (2) is closed.
With heavy engine load and high ambient temperatures, the bypass duct is closed by the bypass valve (2) not later than at a coolant temperature of 95 °C. The entire coolant must flow through the radiator (C-D). It is therefore wrong to remove the thermostat for an ,,improved" cooling of the engine.
Expansion and overflow tank
Production breakpoint: September 1984
Only for vehicles with air conditioner or automatic climate control.
The drain hose at the filler neck of the expansion tank leads to the overflow tank.
The overflow tank collects the coolant forced out through the overflow hose at high ambient temperatures after the engine has been switched off.
After the coolant has cooled down, the coolant in the overflow tank returns to the expansion tank due to the vacuum created in the cooling system.
Coolant loss is largely eliminated in this way.
In order to prevent wrong air being drawn in at the expansion tank cap with vacuum in the cooling system. the cap (1.2 bar) was provided with a rubber seal. Only this cap. part No.123 501 02 15, may be used.
Note on repairs
From the installation of the coolant level transmitter the expansion tank has been reinforced and can be used in place of the previous expansion tank together with a plug with gasket and locking ring.
Coolant level indication
The dynamic coolant level indication monitors the coolant level in the expansion tank with running engine.
Components
550 Coolant level transmitter
550a Locking ring
551 Float
552 O-ring
Coolant level transmitter (550) in the expansion tank
Control lamp in instrument cluster.
Symbol: symbolic radiator.
Operation
With the ignition switched on (key position 2) the control lamp lights up dimly and goes out with running engine (function control of bulb).
The coolant level in the expansion tank is explored by a float with permanent magnet (551) attached to the coolant level transmitter.
As from a certain coolant level the contact is closed and the control lamp lights up.
Depending on the driving style, the control lamp will first light up for a short time and later on permanently. If the control lamp lights up. fill up coolant. Electrical circuit diagram see Group 54.
Note on repairs
In order to avoid wrong installation of the coolant level transmitter, it is provided with two lugs of different widths, which engage in corresponding slots in the expansion tank (arrows).
It is pressed into the expansion tank and sealed with an O-ring (552). To remove the coolant level transmitter, remove locking ring.
Engine cooling
A pressure of approx. 1.2 bar is produced in the cooling system as a result of the spring.tensioned cap (code no.120).
When driving at full throttle, climbing a hill or driving tail-to-tail, after driving very fast on a Motorola before encountering a traffic jam or when driving in regions with high outside temperatures, the pointer of the coolant temperature gauge may rise up to the red mark if the cooling system has antifreeze protection down to -37 °C without any coolant being ejected or engine problems occurring.
If the engine is running for lengthy periods without moving, e.g. traffic jam, it is recommended to shift the selector lever on vehicles fitted with automatic transmission into position "N". This reduces the amount of heat produced at the transmission and thus also reduces the extent to which the coolant is heated up additionally by the transmission oil cooler.