I had this problem ....Head Gasket or radiator cap
Heat from the engine causes liquid to expand. It used to overflow onto the ground if it caused enough pressure to open the radiator cap. The overflow tanks were installed to automatically catch and return the coolant to the cooling system.
It could be a couple of things. The coolant system could be over full. There could be a clog in the radiator. Or possibly the thermostat but not likely. also, the ford coolant tank is pressure sealed, if the cap to the tank has a defective seal, it WILL overflow when you stop your car, or whenever the pressure builds
the reason why the coolant is spilling up over the reservoir is because the thermostat needs to be replaced because when the engine needs water the thermostat heats up from the engine and causes the springs to expant which opens a seal to allow the water throughout the engine i just realpaced the thermostat in my volkswagen
Pressure in the cooling system can cause water to be forced into the overflow reservoir due to factors such as a faulty radiator cap, a blockage in the system, or overheating of the engine. When the pressure builds up beyond the capacity of the system, the excess coolant is released into the overflow reservoir to prevent damage to the system.
It sounds like the tank has a leak.
Defective radiator caps or tubes
There are a couple of things that can cause oil to get into your coolant reservoir. A blown head gasket or a broken piston ring are the most common causes.
I'm having to guess it's the low coolant light? Possible coolant switch in the overflow bottle is dirty or defective., Is it low on coolant? Possible wiring issue to sensor.
It sounds like you have a blown head gasket. Combustion gases can enter the cooling system through either a blown head gasket or cracked cylinder head. The gases (under pressure) force coolant out of the reservoir. This also causes a void in the upper part of the cooling system , leaving no coolant at the thermostat and the coolant temperature sending unit. The result is a erroneous temperature Reading and will even prevent the thermostat from opening.
Have a plumber snake out the drain. You have some sort of blockage.
if there is oil in the coolant system it could be a crack in the intake, a ruined intake gasket, a cracked cylinder head