Cooling System: Testing and Inspection
Complaint: Pointer of coolant temperature moves into red field while driving, coupled with simultaneous coolant loss.
Cause/Remedy:
1. Correct coolant level and vent cooling system by intermittent acceleration, with heating system fully opened.
Attention! The expansion tank closing cover may be opened only at coolant temperatures below 90 °C. Initially, turn to first detent only and evacuate overpressure. Danger!
2. Check tension of V-belts on coolant pump and correct. Drive Belt
3. Check radiator ribs for external dirt. Blow out contaminated radiator with compressed air from engine end.
4. Check cut-in point of temperature switch for auxiliary fan. Model 116 (100 °C) in coolant thermostat housing, models 123 and 126 (52 °C) in receiver dehydrator of air conditioning system or automatic climate control.
5. Check operation and direction of rotation of electric auxiliary fan.
6. Check coolant thermostat. Thermostat
7. Check viscofan coupling. Fan Clutch
8. Check vent line between coolant pump and cylinder head for unobstructed passage.
9. As an experiment, install a new radiator. Radiator
10. As an experiment, replace coolant thermostat housing, while paying attention to unobstructed access from cylinder head to coolant thermostat housing.
11. Remove coolant pump and check impeller for tight seat with coolant pump warm (warmed up in water bath). Check coolant pump housing for cavitation (washouts).
12. Check pressure loss on warm engine with expansion tank completely filled (pinch overflow hose). Keep watching coolant surface for formation of bubbles.
In the event of bubbles, replace cylinder head gasket and check cylinder head for distortion and cracks.
NOTE: Watching of coolant surface with expansion tank closing cap removed and engine running will often result in wrong diagnoses.
Immediately upon removal of expansion tank closing cover the overpressure in cooling system is cancelled and the boiling point is reduced. Even though the coolant temperature readout is not yet indicating 100 °C, the different temperature in cooling system may result in vapor lock, even though no fault exists. Vapor lock will often result in the wrong diagnosis of "cylinder head gasket leaking".
13. Remove rust and sludge residue, as well as boiler scale from cooling system.
Complaint: High coolant temperatures on vehicles up to July 1983
Cause/Remedy: Install coolant pump pulley with smaller dia. For this purpose, use modified V-belt (9.5 x 1000). Also install a 6-blade plastic fan (previously 6-blade) and reinforced viscofan coupling.
Spare parts
Complaint: Engine not getting warm.
Cause/Remedy:
1. Remove coolant thermostat. Service and Repair
2. Check sealing seat of coolant thermostat for foreign particles (molding sand, machining chips) and remove such particles. Replace coolant thermostat only if thermostat is damaged or if the sealing surfaces are distorted.
3. Thoroughly flush engine, if foreign particles are repeatedly showing up. For this purpose:
a) Close all coolant hoses.
b) Remove coolant pump with coolant pump housing and coolant thermostat housing.
c) Unscrew coolant drain plug on cylinder crankcase and radiator.
d) Flush engine housing and radiator with a strong water jet.
e) Flush heat exchanger. For this purpose, turn key of starter switch to position "2".
On model 116, push "DEF" button and short heating water pump. On models 126 and 123 (with automatic climate control), push "DEF" button. On model 123 with and without air conditioning system, set lever of heating system to full heating capacity.