Your vehicle is full of fluids and gaseous vapors, and the main method of moving those fluids and vapors is through hoses. You probably already knew that, but what you may not know is that nearly every one of them is designed for a singular purpose and not interchangeable with other systems. That is right; your fuel will eat right through a vacuum line or heater hose, and your transmission fluid requires a specific type of hose as well. While you may look for a hose that is cracked and brittle before replacing, the real culprit is on the inside. The pressure of the fluid flowing through the hose, mixed with contaminants, is what wears out hoses. Just because it is liquid does not mean it isn’t causing wear, one look at the Grand Canyon will disprove that notion. Here’s what you need to know about automotive hoses and where to use them.
Types Of Hoses
These are the most common hoses you will come across when working on your vehicle.
Low Pressure Fuel Hose
Low pressure fuel systems (like the kind used in carbureted vehicles ) see maximum pressures between 6 and 10 psi. It is fairly flexible, easy to cut, and easy to work with on most vehicles. Most flexible fuel line is made of black nitrile with nylon cords between the layers for strengths. This hose is typically good for pressures up to 25 psi, beyond that you need EFI hose. Standard fuel line is capable of supporting gasoline, diesel, biodiesel, ethanol, and oil without issues. It can be found in custom molded shapes or in rolls that allow you to cut whatever length you need.
High Pressure Fuel Hose
Designed for the higher pressures of an EFI system, typically with a maximum pressure range of 30-100 psi depending on the hose. The clamps used on these hoses need to be rounded, a standard flat worm-drive clamp can cut into the hose. Instead, use the rolled edge clamps designed for EFI applications. Of course higher pressure applications should have specialty fittings instead of hose clamps.
Coolant hoses come in two flavors – heater hose and radiator hose. They hoses are made the same, but the sizes are real difference. Heater hose is generally ½, 5/8, and ¾-inch in diameter. There are different types of heater hose, from standard to heavy duty. The heavy duty hoses have extra protection from exterior abrasion and damage. All heater hoses are lined with nylon cords for durability. They can be molded into specific shapes or generic straight lengths ready to custom cut from a loose spool. Coolant hose is not safe for fuel of any kind.
Radiator hoses are also lined with cords, but they are typically molded to shape to help prevent kinking and for better flow. These hoses can be anywhere from 1-inch up to 3 inches in diameter, and are designed to resist collapsing. Some radiator hoses have large springs inside them to ensure they do not collapse. A radiator hose can collapse as the hot coolant cools, creating a vacuum.
There are several hydraulic systems in most cars, namely power steering and brakes. Both require high-pressure hoses that can handle 2,000psi or more. These hoses are user-replaceable, but unless you have special equipment to form the end connections you can’t just make your own hose. These hoses have special compressed fittings that secure to the hose to hold the high pressures. These hoses are lined with braided steel between the layers. This makes the hose very stiff and hard to flex or bend.
The one exception is the power steering return line hose, which is not under much pressure. These can be cut and secured with standard hose clamps. Your automatic transmission is also a hydraulic system, and the fluid has to be cooled. This is done through hard lines that connect to the radiator. There is a rubber line that serves as a flex joint, this must be hydraulic hose. Most modern cars have specialty lines that are vehicle specific, but many older cars just use a length of rubber hydraulic line. This is fairly low pressure line.
Your vehicle’s air conditioning system requires specialized high-pressure hoses to contain the refrigerant inside the system. This is similar to the high-pressure hydraulic hoses, but instead of the braided steel layer, these hoses have a braided nylon for strength and flexibility. Similar to the hydraulic hoses, A/C hoses requires special equipment to attach the fittings.
There are two types of A/C hose – barrier and non-barrier. This is for the two main types of A/C refrigerant. The modern R134a/R1234yf type has smaller molecules than the older R12. If you put R134a or R1234yf in R12 non-barrier hose, the gas will slowly seep through the hose itself because the molecules are so small. R12 molecules are bigger than the molecules of the hose, so it does not seep out. R134a and R1234yf require a barrier-type hose, which uses a plastic liner that contains the refrigerant.
Even modern cars still use vacuum lines, albeit less than older vehicles. Vacuum line can be rubber, PVC, or silicone. Vacuum hose is capable of handling 25psi, and is designed for vacuum, windshield washer fluid, and radiator overflow use.
Compressed Air Hose
Some vehicles use compressed air for various systems such as air ride suspension, air brakes, or even an air horn. This is not the same kind of air hose you would find in a shop. It is designed for the rigors of use on the road and with special fittings.
Checking Your Hoses
Hoses are wear times and they have to be checked and replaced periodically. Some hoses should just be outright replaced on a regular basis, as they are hard to check, but others are easy to determine if they are wearing out. Fuel lines should be replaced every five years. Sure, your car may be 30 years old and you have never replaced a line, but that is not a good thing. The fuel itself eats at the hose, even though it is fuel line. This leads to small pieces falling into the fuel and gets trapped in the filter or in the carburetor or EFI system. Eventually, the hose will split.
Coolant lines are easy to test. With the engine cool, grab the hose and give it a squeeze. It should resist your grip but eventually give. If it is soft, change it as soon as possible as it is thin and could rupture at any point. Any hose that has cracks, weathering, or scrapes should be replaced. Frayed cords on the cut end of the hose are not an issue, but if you see cord anywhere else, it needs to be replaced immediately. Oily hoses, especially near a compressed fitting, should be checked carefully, as that could be a sign of weeping through the hose on high-pressure applications. Bulging hoses should also be replaced, as this is a sign of weakened interior walls. Replacing a hose is fairly simple, in most cases, you will lose some fluids which are simply replaced. Some applications, specifically brake hoses, require bleeding of the system. Replacing a power steering or transmission hose means that you should flush the system before refilling with new fluid to evacuate any contaminates from the equipment itself.
Check out all the belts and hoses available on NAPAOnline or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on hoses, chat with a knowledgeable expert at your local NAPA Auto Parts store.
A life-long gearhead, Jefferson Bryant spends more time in the shop than anywhere else. His career began in the car audio industry as a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist ever since. His work has been featured in Car Craft, Hot Rod, Rod & Custom, Truckin’, Mopar Muscle, and many more. Jefferson has also written 4 books and produced countless videos. Jefferson operates Red Dirt Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced.