When a radiator hose breaks it spills coolant under high pressure underneath the hood.
The coolant then gets all over the engine and you'll usually notice steam from under the hood from both the hot engine coolant and because the hot engine coolant getting on the exhaust.
Then your engine will overheat when the radiator hose breaks so you must shut off the engine o prevent further damage because there will be no more engine coolant to cool the engine.
You'll then either need to replace the hoses and add more coolant or get the vehicle towed.
A radiator hose can burst due to too much pressure, bad hose, cracked hose, holes in the radiator hose etc.
As the radiator hose ages it can develop cracks and eventually the radiator hose can burst which can then spill coolant all over the place and leave you stranded and it can overheat your engine.
Dried out rubber coolant hoses can also burst as they become hard and brittle.
Radiator Hoses swell when pressure builds up in the radiator hoses.
A little bit of swelling of the radiator hose is okay but too much swelling of the radiator hose is an indicator of too much pressure built up in the radiator hose.
Too much pressure in the radiator hose could be caused by a clogged radiator or other clogged ports in the engine coolant system.
When coolant near boiling passes through worn old radiator hoses, it increases the pressure in the radiator and in the hoses that connect it to the engine.
Radiator hoses are designed to handle a specific amount of pressure; if that pressure increases to an excessive level, the hose will begin to swell and could burst.
The most common cause of radiator leaks is leaky hoses, but you can have leaks in the radiator itself, too, which can be a bigger problem.
The coolant continually running from your radiator to your hot, running engine and back again creates a lot of pressure.
When a radiator hose goes bad it will usually start swelling, develop pinholes, leak coolant, become too soft, collapse or have cracks in the hose.
If the radiator hose is 8 or 10 years old or older it would be best to replace it before it bursts as it will cause your engine to overheat and leave you stranded.
Inspect the hoses and note any kinks or obvious signs of wear.
Squeeze the radiator hoses (when cool ONLY) and see how they feel.
If hoses are soft and pliable, there is no need to replace them.
However, if hoses feel stiff, crackly, or brittle, they need to be replaced.
The top radiator hose should be hot while the bottom radiator hose should either be cold or just somewhat warm.
The bottom radiator hose returns cooled coolant back to the engine so it should not be hot but the top radiator hose should contain hot coolant and should be hot.
When an engine is warming up, the thermostat is closed, and neither the top or bottom radiator hose will be hot.
Once the thermostat opens, hot coolant will flow to the radiator.
The top hose will be hit, and the lower hose will be somewhat less so.
The engine needs to be really hot and almost overheat before the thermostat lets the coolant pass by.
If your car is not overheating, but the lower coolant hose is cold when you feel it – it may just mean that it is not hot enough, and therefore there is nothing wrong with your engine.
The hot coolant enters by the top hose, is cooled by the radiator and then cooled coolant re-enters the cooling system from the bottom hose.
The top radiator hose is usually but not always the location of the thermostat.
Either way, the top hose gets hot after the thermostat has opened.
The time the thermostat takes to open depends upon factors such as: Coolant temperature.