How hot is it

How hot is it

2007 engines are burning hotter; fan clutches and other underhood components are being challenged

2007 engines are burning hotter; fan clutches and other underhood components are being challenged.

It’s no secret that one of the major concerns related to the introduction of the ’07 heavy-duty engines is the increase in underhood temperatures. While anecdotal information about the increased underhood temperatures of the 2004 engines suggested that hoses and windshield washer bottles were melting and that you could cook a hot dog in the heat emitted from hood side vents, we are not sure if these incidents will be repeated on ’07 engines. But we do know that they run hot.

While there may have been some “worst case scenarios” earlier and, while there are still concerns about underhood temperatures, all is not lost. Engines and component suppliers have been working on ways to compensate for increased temperatures. Unfortunately for fleets, some of the solutions mean replacing components more frequently.

Recently, Fleet Equipment spoke with Darry Stuart, president and CEO of DWS Fleet Management, and Jim LeClaire, president of T.O.P. Inc., about the situation. Both men agree that predictive maintenance, or “maintenance insurance,” is key to protecting engines and underhood components.

The most common component failures have been belts and hoses, but the heat is challenging alternators, fan clutches and other underhood components. When it comes to fan clutches, Stuart says that the demands of cooling the engine compartment are requiring the replacement of these components at regular intervals.

“Fan clutches are running on average 60 to 75 percent of the time to cool the engine,” he says. “As a result, they need regular inspections and need to be scheduled for replacement more frequently. Regular checks of fan blades are needed, as well.”

LeClaire says, “Replacement schedules will vary based  on the operation, and I would encourage fleets to keep failure data to use to determine the replacement cycle. I think it should be noted that failures are not a vendor-specific problem, they are related to engine changes made and fan clutches are just working harder to dissipate heat. Every supplier has had underhood issues.”

Both Stuart and LeClaire agree that the fan clutch suppliers have made some very significant changes in grease and bearing make-up to address the increased heat. However, they urge fleets that are running 2007 engines to be diligent in monitoring all component wear and replace them at regular intervals, which fleets need to pre-determine. They say this is the best way to avoid costly breakdowns.

Component changes
Cooling system fans have changed to handle the higher underhood temperatures of the ‘07 engines. The most obvious change is larger fan blades – and more of them. According to Borg Warner, fan speeds, diameters and pitch have in-creased as well as the addition of blades. The company notes that it has designed its Cool-Logic fan drive as a true multi-speed (infinitely variable) unit that will support higher torque requirements created by the new fans. The unit is designed to engage only the fan to the point where cooling is needed. This improves fuel economy as well as the thermal spikes (cycling) underhood components have typically experienced with all previous fan drives, the company says. This reduction in underhood temperature spikes saves components such as belts and charge air coolers from heat damage. The drive also aims at adding driver comfort because of reduced fan noise and improved drivability. Sales of this unit began in 2007.

As for design changes that may affect performance of the fans, Borg Warner says that the Cool-Logic fan drive will engage the fan just enough to maintain stabilized coolant temperature for any given instance. This results in better fuel economy because typically an on/off drive engages full on whenever any cooling is required.  

There is no maintenance required for the Cool-Logic fan drive. The unit is completely self-contained and completely controlled by the engine ECU. There are no air lines, solenoid valves, or any other control components that have to be maintained.

Borg Warner states that it understands the harsh demands that new engine emissions will play on the parasitic horsepower draw of the vehicle. The company says that its new technology not only will help with the horsepower draw of today’s new engines, but also will help with the life of underhood components as well as fuel economy for any fleet running engines with the new emissions standards.

Torque and thrust
Recent changes to fan clutches have created some challenges.

“Every fan blade requires a certain amount of torque to properly engage, and every fan clutch produces a certain amount of torque,” says Brian Swanson, sales manager for Kit Masters Inc., a company that manufactures rebuild kits and remanufactured fan clutches for the heavy-duty industry. “Due to the recent increase in cooling requirements, the fan blades have become bigger. The new, bigger fan blades are beginning to require more torque than the fan clutches can provide. Fan blades with 10 blades or more, or 30-in. or greater in diameter, while turning at high revolutions, may require more than 2,000 in.-lbs. of torque. If the fan clutch does not provide enough torque to hold the fan blade properly, the fan blade will slip while engaged. A slipping fan blade causes massive internal heat. Massive internal heat causes bearing failure, seal failure, or both.” This, however, is dependent on the vendor and the style of the drive.

Some fan clutch makers have made allowances for this demand. Swanson says, “The current OEM fan clutch technologies advertise between 2,100 in.-lbs and 2,400 in.-lbs. of torque, depending on the model specified. Testing demonstrates slightly lower results (1,600–2,000-in.-lbs.) The new, bigger fan blades are requiring more torque than the current fan clutch technologies can provide.”

Swanson notes that every fan blade produces a certain amount of thrust. “On one of the OEM’s spring-engaged fan clutch, the fan thrust directly reduces the spring pressure. Since spring pressure is one of the key forces in providing torque, the lowering spring pressure will cause the fan clutch to provide even less torque.”

Swanson says Kit Masters has a solution to this problem, “We offer  technology in both a rebuild kit and complete remanufactured fan clutches.”

New PMs
When it comes to cooling system maintenance, in particular fan clutches, for ’07 engines, fleets will need to change to predictive maintenance. They should talk with suppliers, assess operating conditions, and plan to replace parts before they fail.

Heavy-duty vehicle fleet managers are embarking on a new era of maintenance with the introduction of more emission-efficient engines. They are going to continue to run hotter than previous models, and maintenance procedures are going to need to be adjusted to compensate.  

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