How much coolant have to get out of the cooling system?
 

I changed a coolant in my 260E. By manual it should be 9 Liters. I just opened a plug on a radiator and wait until it stops, put a plug back and put a new coolant in a tank but only 5 Liters.
Is my radiator pluged? Or 4 liters deposited somewhere in the engine?

Engine, heater core and hoses.

You need to open the drain valve under the rear exhaust mainfold to completely drain the old coolant. You can place a hose on the nipple for spill free draining.

Since you now have a mix of old and new coolant, I suggest you start over by completely draining the system, then install at least 50 percent MB coolant or Zerex G-05 mixed with distilled water.

You can also flush both the engine and heater circuit from the heater inlet line nipple at the left rear of the head.

Also, I'm suspect of your spec for cooling system capacity. Mine is 10.0 liters and your 260E should be at least as much or maybe a little more assuming it has a slightly larger radiator.

Duke

What if I keep a mix of old and new coolant?

The optimum ability to move heat deminishes below a coolant to water ratio of 60%.

It's analagous to draining 3 quarts of the old oil and adding three new quarts to the remaining 3 quarts of old oil.

Have you changed the oil?

Duke

I would say that refreshed the oil :-) and I need to changed not after 3000 miles but after 1500 miles.
So, if it is just simle mixing solutions and they do not have an effect on each other, I would say I will change a coolant not in 3 years but in 1.5 year?
If it is no contamination of any sort, or catalic reaction inhibition.

Why take a chance? Why not do the job properly? It doesn't cost that much!