Water coming out of overflow

Clarify your question. If it is overheating with the new radiator, how badly?. bubbles in the overflow tank?
Jack up front and take cap off and burp radiator overnight.
One suspects air bubbles, or the wrong water thermostat not opening for whatever reason.ensure water thermostat has a hole drilled through it

If its the electronic 'fan' thermostat, you are addressing the symptom not the problem. If the car has 300kms/150K miles, could be a head gasket leak - exhaust to water. Check radiator fluid for traces of exhaust gas.

Your leak could be anywhere. The radiator, the water pump gasket... If you have a cracked block coolant can leak into the oil-pan or out of the cylinder head etc

It could be a leaking head gasket, or blockage in the cooling system such as sludge in the radiator, or a faulty cooling fan.
How long can you drive it before it gets to 220 degrees, and is the fan coming on ?

any signs of coolant outside car? smell coolant in car? smoking out exhaust colour?

If the coolant is leaking at the head gasket or the intake manifold gasket slowly, then new gaskets will have to be installed. The bubbles coming up is a bad sign that the seal of the coolant system is bad or it's overheating the coolant to the point that it boils over.

The overheating may be due to air or vapor in the cooling system not allowing fluid to flow freely.

Did you put a 50/50 concentration of coolant to water into the cooling system?

Also, check the fan to see if it is turning on when the car is at operating temperature at idle.

May need to be flushed out and new coolant installed to increase cooling efficiency.

Good luck on this repair.

hopefully its just a jammed thermostat,other wise its gonna cost...replace asap.

Rusty is from running a bad or no mix of coolant. (PH level is off) You may have a water pump that has corroded impellers, and can't move the coolant as well any more. I would start by making sure to flush the engine block again, and make sure you flush water through every possible hose, and where you can get at it.

Without more information, it is possible you have a air bubble in the coolant or a blown head gasket. Check the exhaust for smells of coolant (sweet) and the oil for signs of coolant as well, it will look like a milkshake. If you notice an excessive amount of visible bubbles in the overflow tank then more than likely you have a head gasket problem and the cooling system is being pressurized from the leak. To bleed the coolant system, remove the radiator cap and start the car and you should observe small bubbles rising to the top, again if there is an excessive amount then you have a head gasket problem.

That's what it sounds like, a blown head gasket. Every time the piston compresses it pushes the air fuel mixture into your cooling system through the broken head gasket. Try running the engine with the radiator cap off or lose and look and smell for gas in your radiator overflow tank. Good luck and hope this helps.

head gasket most likely.