What’s Your Belts & Hoses IQ?

What’s Your Belts & Hoses IQ?

Belts and hoses are common replacement parts that most part stores stock (at least the more popular SKUs).

How much do you know about automotive belts and hoses? These are common replacement parts that most part stores stock (at least the more popular SKUs). Every motor vehicle on the road has one or more belts, and dozens of different kinds of hoses (coolant, fuel, vacuum, power steering, brakes, windshield washers, etc.). Chances are your store also stocks hose for other types of applications, too, such as air hose for air compressors, hose for welding tank connections, or maybe even exhaust hose for routing exhaust fumes from tailpipes out a garage door.

The point is you need to be familiar with the products you sell so you can help your customers get the correct replacement belts and hoses that match their needs. Selling the wrong product can have serious consequences.

Take fuel hose as an example. There are various types with different pressure ratings. Fuel hose designed for an older, low-pressure carbureted engine may burst if installed in a late model vehicle with a high-pressure fuel injection system. In older vehicles with carbureted engines and mechanical engine-mounted fuel pumps, there was virtually no pressure in the fuel line between the fuel tank and pump (in fact, there was suction), and maybe only 4 to 6 PSI of pressure between the fuel pump and carburetor. For such applications, low-pressure hose is all that’s necessary.

On late model, fuel-injected engines, there is constant pressure from the tank-mounted fuel pump all the way to the fuel injector supply rail on the engine. Depending on the application, the internal line pressure may vary from 45 PSI up to 85 PSI or higher. Fuel hose designed for late model fuel-injected engines must therefore be high-pressure reinforced hose. Such hoses are usually made of a higher grade of material such as fluoroelastomer/nitrile and reinforced with aramid fiber. The hose typically has a rated working pressure of 100 PSI, with a burst pressure of up to 900 PSI. It’s tough stuff and is designed to withstand chemical attack by ethanol, methanol and other common gasoline additives.

The greatest danger occurs when somebody tries to “make do” by substituting a piece of hose that happens to fit the fittings on an application instead of using the correct type of replacement hose for that application. Fuel hose is designed for fuel, not oil vapors. If a piece of fuel hose is substituted for a piece of PCV hose or vacuum hose, the material in the hose may be adversely affected by oil and deteriorate over time. Likewise, if a length of PCV hose or vacuum hose is used in place of fuel hose, it may not be capable of withstanding the pressure in the line or chemical attach by alcohol additives. PCV hose is typically designed for a working pressure of 50 PSI or less (half that of EFI hose), and may have a burst pressure rating of only 250 PSI (less than a third of EFI fuel hose).

It’s the same story with power steering hose. The output hose from the power steering pump to the steering gear has to withstand very high peak working pressures (up to 1,000 PSI or higher!), while the return hose that carries fluid from the steering gear back to the pump reservoir sees relatively low pressure. The high-pressure hose for a power steering system must therefore be reinforced and made of materials that can withstand the effects of PS fluid in the system. The hose also requires special crimp-on fittings that can safely handle this kind of pressure, too. Use the wrong hose or the wrong type of fittings and the hose will fail.

Flushing the power steering system after replacing a failed hose, pump or steering gear is recommended to remove debris from the system. Your customer will also need new power steering fluid, too.

What about coolant hose? The cooling systems in most late model cars and trucks are designed to operate at 13 to 18 PSI or less. So most radiator and heater hoses never see the high side of 18 PSI, even if the engine runs hot and overheats. The spring-loaded valve inside the radiator cap will open at its maximum rated pressure and vent steam and coolant to relieve pressure.

Most coolant hose can safely handle a maximum working pressure of 30 to 40 PSI, which is double of what it will ever see in the real world. Of greater concern is the ability of the hose material to resist deterioration from heat and chemical attack.

The coolant that circulates inside the radiator and heater hoses is usually between 195 to 220 degrees F when the engine has reached normal operating temperature. Quality radiator and heater hoses made of EPDM can usually handle operating temperatures up to 260 to 300 degrees F. But hoses made of cheaper materials may not do so well at elevated temperature.

Most original equipment coolant hoses made of EPDM should easily last up to 10 years or more in normal service. So why should customers expect anything less from an aftermarket replacement hose?

If a radiator or heater hose has failed, chances are the other hoses are also reaching the end of the road and may soon fail too. For this reason, recommend replacing all of the coolant hoses at the same time. You only have to drain and refill the system once (which can be a pain on many late model cars due to air entrapment), and your customer will have the peace of mind that there shouldn’t be any more hose failures for years to come. The coolant should also be changed if it is more than five years old, and replacing the thermostat is a good idea to prevent overheating problems down the road. The radiator cap should also be inspected, and replaced if it leaks or fails to hold its rated pressure.

For ease of installation, replacement hoses should be the same length and curvature as the original. Molded hose designed to fit a particular application is usually the best replacement option (though some trimming of the hose length may be required to fit a specific vehicle). Flex hose and wire-reinforced straight hose are a less expensive alternative and can usually be shaped to fit most applications. As with molded hose, some trimming may be necessary to make the hose fit. In either case, replacing the original hose clamps with new ones is always recommended. Your customer will also need one or more gallons of fresh antifreeze to replace the old coolant that was lost when the hose(s) were replaced.
On some late model vehicles, branched hose is used. This type of hose combines two or more individual hoses into a single hose. The auto makers like this approach because it makes installation easier on the assembly line, and eliminates potential leak points when various hoses are connected with fittings and clamps. The only drawback is that the replacement hose is more expensive than individual hoses, and availability may be a problem if the hose is not in stock.

Most late model vehicles have many yards of vacuum hose and vapor hose that snake through the engine compartment and throughout the vehicle. Vacuum hose is used to route vacuum to the power steering booster and EGR valve, and to siphon fuel vapors from the evaporative emissions canister. On older vehicles, vacuum is also used to help regulate transmission shifting, to control various emission and even change spark timing.

The feature that makes vacuum hose unique is that it is designed to handle negative pressure without collapsing. Vacuum hoses seldom see positive pressure unless the engine backfires, so they carry low pressure ratings. Normally, only air moves through the hoses but it may also carry fuel and oil vapors as well. So the hose material must be capable of withstanding chemical attack as well as high underhood temperatures.

Rubber hoses are used to connect the steel brake lines to the front brake calipers and rear brakes. The hoses must be flexible, and capable of withstanding high pressures (up to 3,000 PSI or higher). Because they are a critical safety component, they are also required to meet DOT FMVSS106 standards.

Brake hoses are made of several layers, including an inner layer that handles the brake fluid, a reinforcing layer (some type of fabric or fiber) that prevents the inner layer from expanding when pressure is applied, and an outer protective coating top withstand road splash and the elements.

The average life of brake hose is not forever, as many motorists assume. It is more like six to 10 years, or even less if a hose suffers some type of road damage that causes it to leak. A leaky brake hose is a very dangerous condition because the loss of fluid can result in brake failure.

Many brake experts recommend replacing the brake hoses in high mileage vehicles whether they are leaking or not when the vehicle gets its second or third brake job. The hoses come with the end fittings installed and are sized to fit specific vehicle applications. The hose must not be too short or it may be pulled apart when the vehicle turns off if the suspension goes to maximum travel. Likewise, the hose must not be too long or it may rub or chafe against steering or suspension components and be damaged. An often overlooked item that may also be required when a brake hose is replaced are the hose support clips on a strut or axle that hold the hose in place. Any customer who is replacing a brake hose will also need new brake fluid, and possibly some specialty tools to bleed the brake lines (which is necessary to remove air so you get a firm brake pedal).

If your store stocks hose for heavy-duty truck air brakes, be aware the hose has to meet DOT safety standards. Hose for truck air brakes is usually reinforced EPDM rubber rated for a working pressure of up to 145 PSI. No other type of hose should be used for an air brake application.

There are three basic types of automotive belts: V-belts and serpentine belts for driving the engine’s accessories (alternator, water pump, A/C compressor and power steering pump), and rubber timing belts for driving overhead camshafts.

V-belts are mostly history now, having been replaced by serpentine belts that allow a single belt to do the work of many belts. Serpentine belts are flat on one side and grooved on the other, but both sides can be used to drive pulleys. A V-belt, on the other hand, grips the pulleys with the sides of the belt. In either case, belt wear can allow the belt to slip and make noise.

The original equipment serpentine belts in most late model cars are made of EPDM rubber, which allows the belts to last up to 100,000 miles (assuming no pulley misalignment, oil contamination or slippage due to a weak or broken automatic belt tensioner).

The same is true for OHC timing belts. Prior to the use of EPDM, which started in the early 1990s, timing belts typically had to be replaced every 60,000 miles. If a timing belt broke on an “interference engine” (one that lacked adequate clearance between the pistons and valves), belt failure could cause a lot of expensive engine damage.

One very important point to keep in mind with respect to serpentine belts and timing belts made of EPDM is that appearances can be deceiving. Belts made of EPDM do not crack and become brittle as they age like older belts made of synthetic and natural rubbers. So it’s difficult to judge the true condition of a belt by its appearance alone. Several belt suppliers now have special tools for checking wear in the belt grooves.

If a customer is replacing a high-mileage serpentine belt, it’s also important to check the automatic belt tensioner. These often become weak or corroded with age, and lose their ability to maintain proper belt tension. If the belt shows much visible flutter when the engine is idling, the tensioner likely needs to be replaced.

On applications that do not have an automatic tensioner (which also includes older vehicles with V-belts), belt tension is maintained by manual adjustment. Tension should be set to specifications using a belt tension gauge.

On some late model vehicles, a “StretchFit” flat belt is used to drive an engine accessory. The belts are self-tensioning and do not have any manual adjustments or a belt tensioner. Installing one of these belts requires routing the belt around the pulleys, then stretching it over the crankshaft pulley with a special tool.

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