Auto Service World
Feature   December 1, 2002   by Jim Anderton

Survival of the Fittest

Belts and hoses use rubber and reinforcement to survive a brutal under hood environment

Life in the engine compartment must surely be as close to Hell as anywhere in automotive engineering. It’s not only hot, but is often soaked with chemicals that are corrosive and poisonous. It’s not a place for weak materials. Rubber parts are particularly susceptible to attack and in the case of belts and hoses, are in close proximity to oil, coolant, grease and chafing from vibration combined with sharp edges everywhere.

Belts take a beating

Major belt manufacturers such as Dayco, Gates and Goodyear all have histories in the tire business and for good reason. Belts are manufactured with technology that’s not too far from tire construction methods, although there are of course, significant differences.

According to Guy Enta, national sales manager for the Engineered Products Division of Goodyear Canada, “constructions vary, either the older ‘envelope’ technology or ‘raw edge’. Of course the two major types are the standard V-belt and the serpentine drive six-rib ‘poly-vee’ types found on most modern engines.”

Envelope construction, as the name implies, encapsulates the reinforcing fibres in rubber and is commonly seen in conventional V-belts, while the “raw edge” described by Guy Enta is exactly that; exposed reinforcement at the belt’s edges. This is frequently seen on serpentine types, and is a direct result of the manufacturing differences between the two types. Goodyear’s Enta describes the processes:

“They are plied rubber and fabric, similar to tire construction. For the serpentine drive belts, the six-rib configuration is molded in. We make it in a large sleeve, which is than slit into the rib configuration required. Belts are actually built backwards on a huge drum from the back out. The profile is actually milled out, cured into a flat belt, then we diamond-cut the ribs.

For V-belts, there are two technologies. In the old technology (envelope) they’re built singularly. They’re cut raw, wrapped in an envelope and cured individually in presses. Now most of the V-belts are made in a huge slab, the identical way to ‘poly-vee’s’, but are slitted without the serpentine rib milling. If they have to be cogged, we use a cogged diaphragm in the mold that forms the cogged configuration into the belt. Reinforcements are polyester, rayon, and in many cases, Kevlar.”

Serpentine types may have replaced the venerable V-belt, but the engine compartment has added new challenges to modern belts.

“The biggest factor in today’s cars is the lack of room under the hood”, states Tom Trojan, belt product manager, aftermarket, for Gates Rubber Company, adding, “it creates higher temperatures. Temperature degrades belts the most, along with oil.”

Belts degrade in several ways, the most common being cracking across ribs and delamination of the belt’s plies. Mechanical damage and abrasion are frequent causes of premature failure, and in all cases incorrect tension is an important contributing factor. The move toward serpentine belts, in fact, has largely removed the traditional tension adjustment service, lulling many technicians into a false sense of security. Failed “automatic” tensioners are a common source of serpentine failures, so a low or medium-mileage failure with otherwise clean and aligned pulleys suggests a closer look.

Belt squeal, although less common with serpentines, is still a customer satisfaction issue and can be cured using the same basic principle of good belt service: Clean, align and tension properly. Gate’s Tom Trojan explains:

“If there’s noise, it’s generally because of two things. One is that the tension isn’t correct. People usually say that the belt has stretched. Belts do stretch a little, but generally they wear on the sides as they sit deeper in the pulley, which causes the loss of tension. Dirty pulleys, or pulleys that are rough, wear the belt. If you spray water on a noisy belt and it goes away, then comes back, there is an alignment issue. If it starts to slip, then it’s a tension problem. Just use a little spray bottle.”

Trojan believes that pulley misalignment is an under-diagnosed problem with modern engines. Why?

“With today’s cars, misalignment is more of an issue than ever because the distance from pulley to pulley is shorter with smaller engines.”

Hoses contain the chemicals

The other fragile, perishable rubber components faced with abrasive and chemical attack are hoses. In one sense they’re similar to belts in that the “rubber” (some are actually advanced plastics) is reinforced with cords to add strength and maintain their shape.

Goodyear’s Guy Enta explains: “There are two ways that they’re made. One is to extrude a tube. If it’s a heater hose, the compound might be coolant-resistant EDPM, although the compounds vary depending on the product being carried. Reinforcement is then added either by braiding, knitting or spiraling it over the tube. A cover is then extruded over the reinforcement and then the hose is cured. If it is a long length hose, it’s cured in that configuration. Curved hoses are built the same way, but are then cut to length and put on a ‘mandrel’ that forms the desired shape. The hose is then ‘cooked’ in an autoclave and then stripped from the mandrel. The finished hose them maintains the formed shape.”

Enta notes that difficult-to-service and complex “intersect” hoses are a consequence of the engine design process: “Hose relative to the cost of the rest of the engine is low, so it tends to be the last thing designed into the engine. You design the engine, then figure out how to connect it up.”

Technicians, however, connect and disconnect hoses frequently, and as automotive technology has changed, so have the driving forces behind hose failures. Heat, for example, is a major factor in the tight under hood environments of modern cars.

“Heat destroys hoses”, states Robert Rinkel, automotive hose product manager for the Gates Rubber Company, adding, “Cars that have overheated seem particularly susceptible. My advice is that when a serious overheating event has occurred is to watch for hose failure later. The three most common hoses to fail are the upper radiator hose, the water pump bypass hose, and the heater inlet hose. Those are three to watch.”

Ozone is also a factor in hose aging, but the most mysterious, and interesting, is electrolysis. Rinkel explains: “Electrolysis is a hidden cause of hose failure. Engineers discovered that with the new engine designs with different metals like aluminum, they were setting up a grounding path through the coolant, sending fine electrical currents through the rubber, degrading it. You can actually test for it using a voltmeter by putting one probe on the battery and the other in the coolant to see if there’s an electrical current. If you see greater than 0.1 volts, there is a problem.”

Rinkel notes that there are two approaches to controlling electrolysis: “We discovered that you should always use distilled water. Minerals will set up a conductive pathway. The current also creates etching inside the engine allowing metal particles through, so the coolant will have conductors in suspension, increasing the conductive pathway.”

Changing to fresh coolant diluted with distilled water can be an automatic service when changing hoses, but the other method is considerably more laborious: checking grounds. The procedure is identical to any electrical troubleshooting procedure, except that the circuits in question will function normally under test. Repairing, cleaning or even adding additional grounds can drastically reduce the current flowing through the coolant stream.

Belt and hose service is as old as the automobile itself, and in principle, it’s still about spinning pulleys and containing coolant. Sensible service and inspection with today’s long-life products win two ways: they add to the bottom-line and improve customer satisfaction. It’s a rare “win-win” scenario for motorist and service provider.

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