1992 500 SL coolant capacity.
 

Does anyone know what the coolant capacity is on this car, I'm trying to replace the coolant by loosening the plug on lower end of radiator and the cap on reservoir, I am not sure if all the coolant would drain by this method.

gracias:)

Not all the coolant will drain. Probably 1/2 a gallon to an entire gallon will remain within the engine block (I'm not too familiar with the M119 but I know its predecessor the M117 holds a lot in the block). You really should remove both of the block drains if you're doing a coolant flush. Anything less is only flushing half the system!

If you have the owner's manual it will tell you within it. I'm going to guess about 3.5 to 4 gallons.