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Underhood temps on the rise

TAMPA, FL - Engines built to meet 2002 emission standards produce cleaner exhaust than ever, but technology such as Exhaust Gas Recirculation has come at the cost of higher under-hood temperatures tha...


PRESSURE COOKER: New engine technology is easier on the environment but the increased heat generated can deform hoses and cook some components.

PRESSURE COOKER: New engine technology is easier on the environment but the increased heat generated can deform hoses and cook some components.


TAMPA, FL – Engines built to meet 2002 emission standards produce cleaner exhaust than ever, but technology such as Exhaust Gas Recirculation has come at the cost of higher under-hood temperatures that are deforming hoses and cooking components ranging from alternators to belt tensioners.

To make matters worse, the next generation of engines to be introduced in 2007 will include particulate traps that need to run as hot as a whopping 400 F as part of their regeneration process.

The higher temperatures have presented challenges for engineers and fleets alike, speakers said during a recent Technology and Maintenance Council meeting.

Some hoses were never designed to handle the higher heats, said Rod Ward of FlexFab, noting how many spec’s were designed before the latest generation of engines were ever a reality.

A typical AC hose can withstand temperatures up to 257 F, but coolant temperatures have been found to exceed 200 F under typical operating conditions.

Firewalls on the turbo side of the engine alone are reaching 250 F. For now, fleets and owner/operators need to be careful to select replacement hoses that offer added strength, he said.

Some high-pressure fuel and AC hoses, for example, are reinforced with wire braid, and hoses of any sort should also be changed if they become soft and gummy or deformed.

“Hoses near hot exhaust pipes must be shielded or insulated and tethered in position,” Ward added.

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

If designs are failing from exposure to heat, solutions can involve ordering bigger reservoirs or power steering oil coolers (when there’s room to install them), or lengthening power steering lines. And all 45 and 90 degree bends in the lines should also be removed, he said.

“Every time the fluid turns a corner, the temperature goes up.”

Off-the-shelf cooling fan bearings with synthetic grease can withstand temperatures of up to 250 F, but sustained temperatures of up to 270 F are not unheard of, added 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 said 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, said Randy Andis, director of fleet operations with Remy Inc. (formerly Delco Remy).

Bearings are 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.

Prior to 2002, the temperatures of an alternator’s inlet air exceeded 165 F nine per cent of the time, but since then those temperatures are seen 58 per cent of the time, Andis said of the changing environment.

And that means it’s particularly important to ensure aftermarket replacement parts are up for the job.

Late-model designs, for example, include additional vents.

To make matters worse, emission-related equipment is taking up valuable space under the hood, limiting the flow of air around the engine.

“Hood designs are valuable for aerodynamics…but not so much for (the supply of) underhood air,” said Vince Ursini, of Behr America, a maker of cooling systems.

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

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 admitted.

But random holes aren’t going to help, he added, 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. There’s another risk to consider as well.

“Noise regulations and increased cab noise are concerns as you open up these areas,” Ursini added.

Some problems can be solved through pre-trip inspections looking for damaged hoses or low fluid levels, and fleets should pay close attention to driver complaints about such things as lost air conditioning, Leclaire said.

“If we don’t fix this, we’re not going to be able to handle ’07.

“But we can be cool again.”


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