There are many different hoses attached to nearly every different car system, and their health is directly related to the overall health of a vehicle. Hoses, since they are typically made of rubber, plastic or other "soft" materials, are prone to wearing out faster than metal parts in the engine, and drivers ought to know how to inspect them for damage and wear, as well as what signs to look for.
Since each hose is used to transport a different type of liquid, they won't likely deteriorate at the same pace. However, if you're going to inspect one, you might as well just poke around and check out the others as well. Even if you're not sure what hoses belong to which system, you can still check to see if they may soon need to be replaced.
The first and most important step is to turn the engine off and let the car cool down. You may not need to touch any metal parts that could be hot, but it's better to avoid accidentally bumping into a hot part and burning yourself. The first thing you can do is visually inspect the hoses for signs of wear and tear. You should bend and turn the hoses to check for cracks that may be nearly invisible. You should also make sure that the shape and diameter of each hose is uniform, as any bulging or sagging is a red flag that the hose should be replaced.
Hoses for many of the car systems, such as the fuel delivery and cooling systems, can have different specifications that affect the way they should feel. A gasoline-powered vehicle will have more pliable fuel hoses than one driven by diesel fuel, for example. Regardless of which type of fuel the vehicle uses, the hoses that transport the liquid are designed to withstand it without breaking down from being constantly in contact with the fuel. Fuel hoses are typically only found on older vehicles. Newer engines that use fuel injection generally don't use rubber hoses.
Radiator hoses are designed to carry coolant to and from the engine, and are designed to handle high temperatures transferred to the liquid from the engine. As such, radiator hoses are typically made of thick, durable rubber. Similar to these are heater core hoses that transfer engine heat to the heater core inside the dash to keep passengers warm in the winter.
There are still other hoses that are responsible for transporting air from the air filter to the intake manifold so the oxygen can be sent into the engine to mix with gasoline. If these are damaged, it can affect the gas-to-air ratio, which can have an adverse effect on a car's fuel efficiency.
Pliability is key when it comes to nearly any hose, although the level of elasticity may vary between different types. No hose should be so stiff that it is unmovable, nor should they be as soft and bendable as a string. You should be able to wiggle and squeeze the hoses. If those that should be stiff are soft, or bendable hoses are hard, they will likely need to be replaced.
Keeping an eye on the health of your vehicle's hoses will help you catch problems before they get too serious and prevent your vehicle from running rough or leaking essential fluids. It is especially important to inspect hoses regularly if you live in a colder climate, as low temperatures can wear them down faster.