Is your W124 losing coolant rapidly?
Check for signs of leaks around the connecting rubber hoses to the radiator, thermostat housing and engine cylinder head. Check also for water stains at the coolant expansion tank cap itself.
If external leakage signs are not present (ie water stains), it may mean the coolant is leaking into the combustion chambers via a damaged engine gasket or worse a cracked cylinder head.
Signs to watch out for :
- High engine temperature that does not come down.
High speed fan will be on most of the time as the coolant system is unable to cool the engine properly. The engine temperature will continue to overheat to >120 degrees if the engine continues to run. It is highly advised to stop the engine once it reaches 120 degrees celsius to prevent any further heat damage to the engine and relevant components.
- Trumpeting coolant expansion tank cap when at high coolant temperatures.
Combustion gases entering the radiator coolant system, via deformed gaskets or cylinder head cracks, build up pressure in the coolant system. The expansion tank cap is made to release additional pressure by means of a spring loaded valve that opens when pressure builds up to more than 1 bar. The release of pressure will sound like a turbo blow-off valve trumpeting in short bursts.
- Highly pressurized radiator hoses.
Check the morning after a long cool down if the radiator hoses are still pressurized. Gently squeeze across the diameter of the radiator hose entering the radiator near the top of the engine bay. If it is tight and hard, that means that combustion gases are in the system. Next, check if the radiator is cool before uncapping the expansion tank cap. If a gush of air is released upon opening the cap, that proves again that there are internal leakage where combustion gases are entering the system and the pressure causes coolant to escape via the cracks into the combustion chambers and also via the expansion cap spring release valve. And once the pressure is relieved, close the cap and squeeze the hoses again, they should now be soft and flaccid. With a proper radiator system without gaskets or cylinder head issues, the condition of the hoses should be soft and flaccid in the morning after a long cool down overnight.
When all of the above signs are present, the best action to take will be to bring the W124 to a workshop and have them remove the cylinder head to access the damage of the head or gaskets.
Many of such heat damage may be resulted from poor combination of the coolant thermostat and high speed fan switch. Read here for more info on the 2 configuration settings.