Urgent HELP Please Coolant/Flush question

[Merc1]

Hi all
Can someone please tell me about this Flush and Fill situation..
I am leaving for a long trip

Thanks is advane.

Opened the T-Stat housing, put the garden hose with running water in reservoir, started the car, turn the heat in car all the way up, saw water coming out of TS assembly, little splashing all over , since the engine is running and water is hitting the fan and belt, no big deal.

Anyway, after running for 7-10 min I saw only clean water coming out of T-Stat Housing. Car OFF
I replaced the T-Stat housing, and poured in 1 gallon on MB antifreeze into the resarvoir, then I started to add water, only the resarvoir took 1 quart of water.

WHY. The system is for 10.6 Quart. and I only put in 4 quart Coolant and 1 quart of water..it is full, after driving for 1 hour it is still full.... You think remaining 5 quarts in the engine is water? Or is it old mixed up coolant?

Is my system completely flushed? Or does it have too much Coolant, if other 5 quart is old coolant and water....
Thanks
1998 e320