The reinforcement in the Toyota radiator and coolant hose's polymer construction makes it possible for those coolant components to last for a considerable amount of time. However, due to the extreme conditions the radiator hoses experience from the temperature fluctuations of the engine, they will eventually breakdown in time and begin to leak. While all of the coolant hoses will experience this temperature fluctuation, it is the upper radiator hose that will be exposed to the highest level of temperature variations over its lifetime on the Toyota. This is the hose that is directly connected to the thermostat housing on top of the engine where the hottest coolant is released to the cooling system. The connections of the Toyota radiator and coolant hoses to the radiator are another place where the high temperatures negatively affect the polymer makeup of the hoses. This negative affect is the thinning of the polymer sides of the hoses which can be seen by their expansion outwards. Many technicians call this the ballooning of the radiator hoses. When this condition is present on your Toyota, it is only a matter of time before a leak will occur. This leak can be either the seal at the connections not being able to be maintained or a pinhole is created in the hose itself. The time frame for the replacement of the radiator and coolant hoses is dependent on just how often the vehicle is used and the duration of each time it is driven. What should be considered by the Toyota owner is that if one of their hoses is in need of being replaced, both of them should be. This is because both hoses will be close to the same condition.