Hi,
I wanted to increase cooling by simply submerge radiator in water and glicol container. Is it good idea and why not?
What are you going to cool? A nuclear reactor?
Without forced convection it won’t be very efficient. I would start with attaching a traditional air cooler first and seeing if that is enough. Even a small breeze increases efficiency of a radiator quite a bit.
Sure. One of those $10 nuclear reactors they sell in the big box stores.
My response to eelik is kidding of course. If I guess that you want to cool a CPU heat sink of some sort; I would think that water cooling will develop problems over time such as deposits decreasing effectiveness, or maybe leaks. So…what are you trying to cool?
You transfer heat to the container until it ‘fills up’ with heat. Might work for a quick, but short period of time depending on the what you are trying to do. You’ll need another radiator to cool the immersion fluid.
12 Peltier elements. ElectroBOOM made an experiment and has proven, that big radiator with big fan is not enough.
My idea was, that the area of container will be big enough for cooling. I can also get handful of aluminium cans with cut tops and make container stand on it so the surface of will be like 3dm2 for each can16143866348726461199213540524208|374x500
Usually I get water cooling by putting water in radiator. 
You need to maintain a temperature gradient in order for heat to flow. As your sink warms up, the heat flux reduces. You have to move the heat elsewhere to maintain the gradient - with a pump for instance or ensure that the heat capacity and flux of the whole system is sufficiently large to cope with the input and remain within your desired range - for example when operation never reaches a steady state as maximum heat input is transient.
You have not specified the conditions but there are helpful calculators available , e.g. https://www.engineeringtoolbox.com/conductive-heat-transfer-d_428.html
tf does this have to do with kicad or even pcbs?
Fair point especially since this is the kind of topic that can get out of hand rapidly.