It can be either coolant escaping or piston blow by sending fumes out of the breather,you need to find out which.If the coolant level isn't dropping you know where to look next.Not sure what blocking the breathers will prove.Is it overheating,which it will if the head gaskets gone

Test the coolant for combustion gases with a test kit. Although from your description it looks more like excess piston ring blowby or crankcase breather issues.

Edited January 25, 20188 yr by dadof2

If you suspect blow by. A simple check on the colour of the spark plug and a compression test will confirm it for you. Then you’d just have to investigate if it’s rings or an exhaust valve. 

If that’s all good and you think it’s coolant, pressure test the cooling system. OR drain and replace with new coolant at right mixture OR replace with something like Evans waterless coolant (it’s oil based with no water content, so it won’t create any steam).