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serpentine belt radiator hose

Automotive Belt & Hose Replacement

by Larry Carley copyright

According to the Car Care Council, nearly 30% of the vehicles they have inspected have belts and/or hose that need replacing. Yet in most cases, the vehicle owners were totally unaware of the condition of these critical parts.

Everybody wants a reliable vehicle to drive, but not many people are forward-thinking enough to practice preventive maintenance beyond the barest of basics. After all, preventive maintenance costs money and nobody likes to spend money "unnecessarily." We put unnecessarily in quotes because we want to emphasize the fact that most consumers do not appreciate the benefits of preventive maintenance when it comes to belts and hose. Changing the oil and filters every so often they can understand. Oil and filters get dirty and need to be changed. Replacing spark plugs periodically they can also understand. Spark plugs wear out and can become fouled. But replacing radiator and heater hose that have not yet failed? No way.

What people often learn the hard way is that belts and hose age, and what happen when they fail. The coolant leaks out and the engine overheats.

Most belts and hose fail from the inside out. Rubber hose (which are actually made of neoprene or other synthetic materials) can deteriorate with age and exposure to heat. Today's hoses can last 8 to 10 years with no problems, but eventually the hose material will become hard and brittle. Tiny cracks develop in the rubber which eventually cause the hose to split, blister or leak. Oil on the outside of coolant hose can also accelerate the breakdown of the hose material. This type of deterioration can usually be seen on the outside. But what often escapes detection is what is going on inside hose.

Today's bimetal cast iron/aluminum engines and aluminum radiators can create conditions that set up an electrical current in the coolant. The inside surface of the hose becomes a conductor, which causes the material to pit and weaken. Cracks and striations tend to form near the ends of the hose that eventually eat through from the inside out causing the hose to fail. Yet until the failure occurs, the hose may look good as new on the outside.

This type of deterioration can sometimes be identified by pinching hose near each end with your thumb and fingers. If you feel "ridges" or "voids" inside the hose, it is experiencing electro-chemical degradation (ECD) and needs to be replaced. But even this type of inspection may not catch all the bad hose that are out there.


WARNING: DO NOT attempt to loosen or remove a coolant hose or fuel hose on a hot engine. Wait until the engine cools.

If replacing a coolant hose, loosen the radiator or reservoir cap to depressurize the cooling system.

If replacing a fuel hose, the fuel line can be depressurized by locating the schrader test valve on the fuel injector fuel rail and depressing the valve. Or, you can locate the fuel pressure regulator on the injector fuel rail and apply vacuum to the regulator with a hand held pump. Or, you can momentarily start the engine, remove the fuel pump fuse or relay and let the engine run for a few seconds until it stalls from a lack of fuel.


Replacement hose must be the same type, size and length as the original. Original equipment ring type clamps (which may lose tension with age) on coolant, fuel, vacuum or emissions hose should be replaced with screw clamps.

If a coolant hose does not seem to fit properly, try switching it end for end. The inside diameters of the ends may be different depending on the application. Molded hose is also designed to fit one way.

Never pry a coolant hose loose with a screwdriver or similar tool. Doing so can crush or damage the pipe connections on the heater core or radiator, creating a potential leak path. If the hose won't come off, it should be slit with a knife and peeled off.

A good time to replace coolant hose is when changing the water pump or radiator. New hoses might also be needed if the engine itself is being replaced or overhauled. Hoses with over 100,000 miles of service should be replaced.

When replacing an upper radiator hose, pay close attention to the condition of the thermostat housing, too. Aluminum housings can become badly corroded with age and may not seal properly when the new hose is installed. If the housing is pitted and rough, replace it.


Fuel, emissions and vacuum hose are made of special materials because of the liquids and vapors they carry. Fuel hose is made to withstand gasoline and alcohol, and is reinforced to hold pressure.

A fuel hose is usually good for up to five years of service. The reason they need replaced is due to internal flaking of the hose which releases small pieces of rubber that can end up plugging fuel injectors or carburetor circuits.

The pressure rating is printed on the hose, so be sure you use the correct type of fuel hose for the application. Hose that is pressure rated for carbureted engines (7 to 10 psi) must never be used on fuel injected engines (35 to 80 psi or higher). The higher rated EFI hose can always be used on a carbureted application but never the reverse.

High pressure EFI hose often require special high pressure "rolled edge" clamps rather than standard clamps or spring clamps. Some EFI hose also use special connectors.

PVC emissions hose is designed to withstand oil and fuel vapors, but is not designed to handle internal pressure like fuel hose.

Emission hose need replaced when age-weakened rubber collapses under vacuum, which prevents the necessary venting of crankcase blowby vapors through the PCV valve. Hose also will become plugged with accumulated crud that blocks the flow of air through the PCV system, causing sludge to build up rapidly in the crankcase. If not corrected, this can lead to oil breakdown and major engine damage for the customer.

The PCV hose should be inspected (and replaced if necessary) when the PCV valve is inspected (typically every 50,000 miles).

Vacuum hose are designed not to collapse under vacuum, but they are not intended for carrying liquids, gasoline or oil. So be sure to use the correct hose application for the job.

Replacement of vacuum hose is important in the sense that if one develops a leak, it can lead to all kinds of driveability and emissions headaches.

Fairly expensive when compared to other types of hose, power steering hose usually is not replaced unless it is leaking. However, power steering needs to be inspected periodically for leaks or damage because such a hose failure can cause a loss of power steering assist.

Power steering hose comes in two varieties: low pressure hose for the return line, and high pressure for the supply side. Using the right hose is critical. Flushing the power steering pump, hose and steering gear is also recommended after hose replacement if the old hose were flaking internally.

Air conditioning hose comes in two basic types: barrier and nonbarrier. The latter is okay for older vehicles that have R-12 A/C systems, but is not recommended for newer vehicles or those that have been converted to R-134a refrigerant. If a leaky A/C hose is found to contain sludge or debris, the system should be flushed and an in-line filter installed to prevent orifice plugging and to protect the compressor.


Belts likewise deteriorate with heat and mileage. Every time a belt passes around a pulley, it bends and flexes. This produces heat in the belt which hardens the rubber over time. The wear process can be greatly accelerated if the belt is loose and slips. The additional friction between belt and pulley will make a belt run even hotter. After millions of such journeys around the pulleys, even the best drive belt begins to suffer the effects of age. The rubber begins to crack and fray, and the internal cords become weakened and brittle. Eventually the belt breaks, and at that point, all cooling is lost along with whatever other functions were powered by the belt (water pump, alternator, power steering, air conditioning, etc.).

You can't always determine a belt's true condition by appearances alone. Any belt that is obviously cracked and frayed should be replaced. But with many of today's "bandless" belts, there is no outside cover to peel loose and betray the belt's deteriorated condition. A belt may appear to be like new on the outside yet be on the verge of failure because of weakened cords inside.

Most V-belts look the same on the outside, though there are significant differences inside that affect the life of the belt. One of the most obvious differences is in the placement of the tensile cords that hold the belt together and prevent stretching. Tensile cords are usually made of twisted polyester and run the length of the belt. Additional reinforcement is provided in the "undercord" area of most belts through the use of crosswise layers of fabric. Some manufacturers use chopped fibers blended into the rubber.

Placement of the reinforcing tensile cords in the belt can affect belt life. One can see where the larger cords are placed by looking at the sides of the belt. "Center cord belts" have the tensile cords near the center and are less costly to manufacture because they produce less waste during cutting and trimming operations. Other belts, called "high cord belts," have the cords positioned closer to the top.

Positioning the cords at the widest part of the "V" allows up to 40% more reinforcing cords to be used, which makes for a stronger belt. Therefore, high cord belts usually last about four times longer than center cord belts.

But all high cord belts are not long-life belts. If the manufacturer uses low-quality materials and does not get a good cure when the belt is vulcanized, that particular high cord belt may not last as long as a center cord belt.

Another variation in V-belt designs is the notched belt. Though not used as original equipment, it is offered as an aftermarket replacement. The notches make the belt more flexible, which reduces friction and heat buildup as the belt bends around the pulleys. The notches also help to dissipate heat, and the cooler the belt runs, the longer it lasts.

A modification on this theme is a notched V-belt with the cogs facing out instead of in toward the pulleys. One manufacturer says reversing the cogs aids cooling even more, which can help the belt outlast conventional V-belts.

The problem that is guaranteed to shorten belt life is slippage. Slippage creates heat that glazes and hardens the belt, making it more prone to cracking and premature failure. Symptoms of slippage are noise or chatter, and it is evident by viewing glazed or shiny sidewalls on the belt.

Serpentine belts (flat ribbed belts), which are also called "Poly-V, Poly-Rib and Micro V" are so named because of the snake-like path they often follow around the pulleys. The flat design reduces heat buildup in the belt so the belt generally lasts longer than a comparable V-belt. A recommended replacement interval for serpentine belts suggested by one manufacturer is every 50,000 miles, or sooner if the belt has become glazed and is making noise. But most serpentine belts will typically go up to 70,000 miles or more with no trouble, while ones made of EPDM rubber on late model cars will often go over 100,000 miles or more before replacement is necessary.

serpentine belt made of EDPM rubber
Belts made of EPDM are long lasting and should not crack

A loose belt should be retensioned back to the manufacturer specs using a tension gauge. The old rule of thumb about leaving a half inch of deflection between the two furthest pulleys is not very accurate, and, unless a gauge is used, there is no way to know if the belt is too tight or not tight enough. Too much tension on the belt increases strain on the tensile cords, which shortens the life of the belt, as well as the life of the shaft bearings on the accessories.

Belts can also wear as they accumulate mileage. A high mileage belt made of EPDM may still look good as new (no cracks) after 100,000 miles, but the grooves in the belt may be worn to the point where the belt slips under load. For more info on how to check belt wear, Click Here.

Deep cracks in a belt are usually an indication of age. Such a belt is likely to fail soon and should be replaced. But cracks may also indicate an undersized alternator pulley (the alternator may have been replaced previously). The smaller the radius of a pulley, the more the belt flexes with each revolution. This increases heat buildup and shortens the life of the belt. If the pulley grooves are worn or if the belt is too narrow for the application, that can also make a belt ride too low in the pulley. A belt should ride flush to 1/16" above the edge of the pulley.

A misaligned pulley is usually the culprit for a twisted and reversed belt. Pulleys should be parallel and be within 1/8" of alignment of each other. Alignment can be checked with a straight edge. If a pulley is cocked slightly with respect to the rest, it can twist the belt and turn it inside out.

A loose belt or one with broken cords inside can also twist. With a serpentine belt, a misaligned pulley may throw the belt or wear away the belts directional ribs.


WARNING: Keep fingers, hair, loose clothing and tools away from belts when the engine is running!

Probably the fastest way to ruin a new belt is to "stretch" a V-belt over a pulley instead of loosening the accessory designed to slip it into place. As mentioned earlier, the tensile cords in the belt are there to prevent it from stretching. Forcing it over a pulley can break these cords, causing the belt to fail soon thereafter. There are some exceptions, however. On a growing number of late model vehicles, no automatic belt tensioner is used and the belt is stretched over the pulleys to install it. This requires a special type of serpentine belt that is designed to stretch slightly.

Oil and grease can also ruin belts. Petroleum-based lubricants attack rubber and cause it to become soft and spongy. Oil also attracts dirt and grit which can act like an abrasive against the belt. Noise, however, is always an indication of trouble, and the cause, not the symptom, should be treated. Noise may indicate a loose belt, a misaligned or bent pulley, bad shaft bearings in the water pump, alternator or another accessory.

A burr or nick in a pulley can also cut short the life of a new belt. These pulley imperfections will scour the sides of the belt and wear streaks into it. The belt will lose tension, slip and wear all the faster.

When replacing belts, keep in mind they must be the same type, width and length as the belts being replaced. Compare the old and new belts to make sure. V-belts should be adjusted and checked with a tension gauge. Most serpentine belts have an automatic tensioner making adjustment unnecessary.

When replacing a serpentine belt with a spring-loaded idler pulley, check the condition of the tensioner if the old belt was glazed and making noise. Loss of tension with accumulated mileage is not unusual, so, if the tensioner is weak, jammed, noisy or badly corroded, replace it.

When changing a timing belt on an overhead cam engine, the pulleys should be inspected for alignment and wear. Belt tension must be set to manufacturer specifications.


Belt manufacturers say the incidence of V-belt failure rises sharply after three years of service, and four years with serpentine belts. Hose manufacturers say hose failures go up after four years of service. The average passenger car or light truck typically racks up 60,000 to 70,000 miles in four years, so any vehicle that is more than four years old is a potential candidate for belt and hose replacement.

But what happens if never replace your belts or hoses? Hopefully nothing because nobody can predict when a belt or hose will actually fail. But if a failure does occur, the consequences can often be far more serious and expensive than a breakdown and a tow. Overheating is the biggest danger. Depending on how hot an engine gets, the consequences may include a blown head gasket, a cracked or warped cylinder head and/or broken or frozen overhead camshaft.

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