19th Annual Technical Forum: Belts & Hoses

19th Annual Technical Forum: Belts & Hoses

When do belts and hoses need to be replaced?

A. Most car manufacturers do not have a specified service interval for the belts and hoses on their vehicles. In fact, General Motors goes so far as to say the belts and hoses on their late model cars and light trucks should last upward of 10 years or 150,000 miles with few problems. Yet according to a recent “Be Car Care Aware” study, one in five cars needs a new belt. It’s probably the same ratio for hoses, too!

In the late 1990s, automakers began using belts and hoses made of more durable materials. Many neoprene belts were upgraded to ones made of EPDM, which does not harden and crack with age like a belt made of neoprene rubber. As a result of this change, the recommended replacement interval for OHC timing belts more than doubled, going from 60,000 miles to 125,000 miles on many applications. Likewise, serpentine belts and coolant hoses were deemed “replace as needed” based on their condition.

Inspection is still important to determine if a belt or hose may need to be replaced. Because high-mileage EPDM belts seldom show much cracking, the assumption is they must still be in good condition so there is no need to replace them. But the belt may be worn, which can cause it to slip and make noise. The V-shaped grooves on the underside of a flat serpentine belt can wear as a result of friction and exposure to dust and other abrasives kicked up by normal driving. Over time, the grooves become deeper and lose their ability to grip the pulleys. This can allow slippage that may reduce alternator charging, coolant flow through the water pump, even power steering assist or A/C cooling. Many motorists may not notice there’s a problem unless the belt also is squealing or making noise.

Several belt manufacturers have simple-to-use wear gauges that can be used to check the condition of a serpentine belt. If a belt shows excessive wear, it needs to be replaced regardless of its age or mileage. Chunking or visible cracking (spaced closer than about 1/4 to 1/8 inch apart) would also call for belt replacement.

If a coolant hose is leaking, bulging, cracking or has lost its pliability (hard and stiff to the touch), it also needs to be replaced.

If any coolant hose has failed, chances are the rest of the coolant hoses are also near the end of their service life and should also be replaced at the same time. The same logic applies to fuel line hoses, power steering hoses, vacuum hoses and brake hoses.

A coolant hose that has failed from the inside out (pitting or fissures) often indicates an electrolysis problem in the coolant. This can be caused by worn out coolant that is overdue for a change (five years is the limit for long-life coolants), and/or poor grounding between the engine, charging system and chassis.

For ease of installation, replacement hoses should be the same length and curvature as the original. Molded coolant 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.

Q. Should the automatic tensioner be replaced when changing a serpentine belt?

A. The automatic tensioner is a critical part of the belt drive system. It should always be inspected when a serpentine belt is replaced or when a belt is experiencing any kind of problem such as slipping, coming off the pulleys, rapid wear, glazing or squealing. Replace the tensioner if the unit cannot maintain proper belt tension, is sticking, severely corroded or is making noise.

One way to detect a weak tensioner is to watch for belt flutter or vibration when revving the engine. A good tensioner should keep the belt taught, while a weak tensioner may allow the belt to slip and vibrate excessively, or squeal.

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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