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20th Annual Technical Forum: Belts And Hoses



Q: If a serpentine belt is squealing should it be replaced?

A. It depends on the condition of the belt (whether it is worn or contaminated with oil or coolant), and belt tension. A worn or glazed serpentine belt can be noisy as can a belt that has been contaminated with motor oil, grease or coolant. But even a relatively new belt in good condition can slip and squeal if the automatic tensioner is weak or the belt is not tensioned properly.

An automatic belt tensioner maintains belt tension by spring tension. A stiff coil spring inside the tensioner pushes the tensioner arm and pulley outward to keep the belt tight. Over time the spring may weaken or break. The pivot arm may also stick or bind as a result of rust and corrosion, preventing the tensioner from exerting adequate pressure against the belt.

Symptoms that would indicate a need for a new belt tensioner include excessive belt flutter when the engine is revved, noise from the tensioner pulley bearings, visible wobble or looseness in the tensioner pulley, binding or dragging in the pulley bearings (the pulley should rotate freely and quietly), or belt squeal immediately after engine start-up, when turning or turning on the A/C.

Sometimes belt noise may be the result of someone having installed a replacement belt that is the wrong length. If a belt is too long for an application, the tensioner may not have enough travel to keep the belt tight. Markings on the base and arm of an automatic tensioner indicate the tensioner’s minimum and maximum range of travel. The indicator should usually be about half way between the minimum and maximum marks. If the indicator is at or near the maximum mark, it means the belt is worn and needs to be replaced.

Q. What could cause the premature failure of radiator or heater hose at low mileage?
A. Coolant hoses are fairly durable and can last many years without leaking. Heat and ozone accelerate the normal aging process that cause natural and synthetic rubbers to lose their elasticity and become hard and brittle. EPDM hoses are more durable in this respect, but they too can deteriorate after many years of service.

If a coolant hose fails at unusually low mileage, it may signal something unusual is going on inside the cooling system (same for a heater core that fails at low mileage). The hose may be failing from the inside out due to electrolysis corrosion. Contaminants in the coolant such as salts or minerals, or depleted corrosion inhibitors in the coolant can allow electric currents to use the coolant as a conductive path.

This can accelerate internal corrosion of vulnerable metal parts (such as the heater core, radiator and other parts) as well as the hoses. Electrolysis can eat pits and lesions into the inside lining of hoses weakening the hose and eventually eating all the way through. If a low-mileage hose has failed, therefore, it should be cut open and inspected to see if the inside has been attacked by electrolytic corrosion. If it has, the cooling system needs to be cleaned and flushed, and refilled with fresh 50/50 premixed antifreeze to avoid the possibility of recontamination with softened water or tap water. If a customer is refilling with full-strength antifreeze, they should mix it in equal parts with distilled water, never ordinary tap water.

New radiator and heater hoses should always be recommended for any customer who is replacing a water pump, thermostat, heater core or radiator. By the time these other cooling system parts fail, the hoses likely need to be replaced too. New clamps also are recommended.

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