This type of problem will give the same effect as a blown head gasket. It will cause the cooling system to appear unstable. It may also cause the upper radiator hose to tear apart as the thermostat decides to open with a great force of hot water.
THINGS TO LOOK FOR
If you decide to put another radiator hose on what you need to do is feel the upper and lower radiator hoses at normal operating temperature, very carefully, just in case the radiator explodes, and they should be almost the same temperature. If one is cold and one is hot, this indicates a sticking thermostat.
To replace the thermostat it will cost $30.00-$90.00 depending on the make and model of the vehicle and also depending on how old the vehicle is. The thermostat housing bolts may break as you try to remove them.
This article is found in the Virtual mechanic CD Rom
You can download it for the price of a latte, but you will learn not to buy a lemon
By Darren Gow-Brown, Melbourne Australia ©2009