2001 s600 Coolant Temp Sensor issues
I would have NEVER thought that there would be an O-ring fitting to hold pressure in the cooling system. THEN I had to remove the radiator on my '03 S600 and found out different. There the upper hose (return to radiator from the block which is actually in the middle of the driver's side of radiator and NOT actually at the top) is a plastic fitting that fits over a the plastic radiator. The O-ring seals the fitting between the two plastic parts and is held in place by a metal clip that holds the hose fitting from sliding off the radiator fitting. Every radiator I have ever seen has a rubber hose held in place by a clamp. This system SEEMS a little precarious but has not leaked since I changed the radiator.
Your fitting has to have some kind of clamp, or more likely-clip, to hold the fittings together. Look a little closer.
Keith



