Auto Service World
Feature   May 1, 2005   by John G. Smith

Hot and Heavy-Duty

Higher temperatures placing added stress on diesel engine components

Diesel engine manufacturers may have been able to limit NOx emissions by turning to technologies such as exhaust gas recirculation (EGR) systems, but the equipment changes have come at a cost–and not simply in the form of steeper prices.

Engines built to the 2002 standards set by the U.S. Environmental Protection Agency (EPA) are also rejecting more heat than their predecessors, leading to hotter operating conditions under the hood.

It’s the type of challenge that should convince jobbers to reevaluate which heavy-duty replacement parts they stock on their shelves. Several fleets report that traditional hoses are being deformed by the heat, while components ranging from alternators to belt tensioners are also failing prematurely.

To compound matters, underhood temperatures are expected to climb further still. The next generation of engines to come in 2007 will include particulate filters that need to reach temperatures as high as a whopping 400 degrees Fahrenheit as part of their regeneration processes, and these all-new components are expected to be mounted close to their respective engines.

A perfect fit isn’t the only issue that needs to be considered when installing aftermarket components on heavy-duty trucks, speakers stressed during a recent annual meeting of the Technology and Maintenance Council of the American Trucking Associations, which establishes many of the trucking industry’s recommended maintenance practices.

Some popular hoses were never designed to handle the higher heats associated with late-model engines, offers Rod Ward of FlexFab, noting how many related specs were established long before the latest emission standards were ever a reality. A traditional coolant hose can withstand temperatures up to 257 degrees F, but coolant temperatures associated with the new engines have been found to exceed 200 degrees F under typical operating conditions, he says as an example.

Firewalls on the turbo side of the engine alone are reaching 250 degrees F.

For now, replacement hoses that offer added strength should always be the preferred alternative for replacements, Ward says. Some high-pressure fuel and A/C hoses, for example, are reinforced with wire braid, and he’s recommending that hoses of any sort should be changed if they become soft and gummy or deformed.

Meanwhile, traditional power steering systems can fail if temperatures reach a constant of 106 degrees F, says Richard Petrut of RH Sheppard. “Seals have a tolerance temperature of 235 degrees, and they’re not forgiving.”

If customers are reporting power steering systems that are failing from exposure to heat, they should be steered toward longer power steering lines, bigger reservoirs or power steering oil coolers. (That is, when there’s room to install the larger components. Spaces under the hood have become more crowded than ever thanks to the new exhaust-related technology.)

Off-the-shelf cooling fan bearings with synthetic grease can withstand temperatures of up to 250 degrees F, but sustained temperatures of up to 270 degrees F are not unheard of, adds Jim Leclaire, manager of field service and warranty for Horton, a maker of front end accessory drives. “We’ve run over 300.

“The bearing is not going to live. The O-rings are not going to live,” he says of the excessive temperatures. “What’s been standard components in the past won’t work today.”

Even alternator designs have needed to evolve to handle the higher temperatures, says Randy Andis, director of fleet operations with Remy Inc. (formerly Delco Remy). Bearings are now being protected by improved grease and seals, rectifiers have been refined to better dissipate heat, wires are protected by new coatings, and internal insulators have been improved. Older alternators that are sitting on the shelf may simply not be able to handle the stress.

Prior to 2002, the temperatures of an alternator’s inlet air exceeded 165 degrees F 9% of the time, but nowadays those temperatures are seen 58% of the time, Andis adds, referring to the changing environment. This means it’s particularly important to ensure aftermarket alternators are up for the job. Late-model designs, for example, include more vents than older versions.

Not only have heavy-duty engines begun to reject more heat, but the added emission-related equipment is further crowding the space under the hood, restricting the cooling flow of air around the engine.

“Hood designs are valuable for aerodynamics, but not so much for [the supply of] underhood air,” says Vince Ursini of Behr America, a maker of cooling systems.

“Its getting crowded in there,” admits Petrut, referring to the 80 cubic feet of space that exists under the typical hood of a Class 8 truck.

Several U.S. fleets have responded with their own makeshift refinements to hood designs. Some have removed splash shields behind the front tire, and others have cut holes into hoods.

“Small changes to panels and body work can reduce heat dramatically,” Leclaire admits. But random holes aren’t going to help, he adds, referring to one fleet that added side vents only to find that they were driving more air under the hood instead of letting heat escape.

The question that remains unanswered is how long the latest generation of engines will last until they require an in-frame overhaul because of excessive component wear or higher oil consumption. Are early signs of carbon piston deposits or soot on the intake manifold an indication of trouble?

Publicly, the engine makers suggest the latest engine designs will last as long as their predecessors. Cummins, for example, recently tore down a series of engines that had accumulated more than 965,000 km of service, and suggested during the recent Mid-America Trucking Show that its tests prove the latest ISX designs will match the durability of those built before 2002. Power cylinder components had worn about 25%, while connecting rods and main bearings were thought to be half-way through their lifecycles.

“The proof is in the parts,” said Tom Kieffer, executive director, marketing for Cummins. “The analysis concluded that the major contributors to engine durability exhibited outstanding results.”

For the interim, however, the immediate heat issues seem to be dominating discussions.

“If we don’t fix [problems associated with heat], we’re not going to be able to handle ’07,” Leclaire says of the array of challenges. “But we can be cool again.”

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