Cooling System Care More Critical
The new diesels with EGR have higher under-the-hood temperatures. Fan drives, belts, tensioners and hoses are all affected.
Jim Winsor
Executive Editor
If your fleet has any of the new '02 truck diesels with exhaust gas recirculation (EGR), you should be aware that under-hood temperatures will likely be higher than what you've been used to. That isn't to say the engines will be running at higher temperatures. Some will. Some won't. But all of them will have more heat to get rid of through higher loads on the cooling system and its components.
At its fall meeting, the Technology and Maintenance Council (TMC) focused on the impact the new engines will have on cooling systems and maintenance — especially on fan drives and belts. Here's some of the advice the experts offered that may help your fleet, especially when temperatures begin to climb this summer.
Most of the large-bore diesels (11 liters and up) using cooled EGR to reduce emissions will be cooling up to 30% of the engines' exhaust streams, which used to flow freely into the atmosphere. This significantly increases the amount of heat the cooling system must dissipate. Some manufacturers have developed a controllable viscous fan drive, which turns faster the hotter it gets. A viscous drive is never completely off. On/off fan clutches will be cycling more frequently, putting increased loads on bearings, seals, clutch facings and belt drives.
Behr America's Tony Ackerman said on the average, midrange diesels will be rejecting 10% to 30% more heat; heavy duty big-bore engines, 15% to 40% more. There are increased cooling needs at low engine rpm and increased pressures in charge air coolers. On high-horsepower engines, some radiator cores are thicker and/or larger.
Many engines will have higher pressure radiator caps than before, and top-tank coolant temps will be up, too. Higher pressures promote leaks both in cores, hoses and fittings, so PM services and daily checks should focus on leaks, he said.
Horton's Jim LeClaire said fan size and fan rpm impact fan clutch loadings. He noted that if fan speeds increase only 10%, the horsepower "pull" goes up 33%. He said some 34-inch diameter fans may have up to 11 blades. Increased fan "on" time will impact fuel economy. He voiced concern about short fan cycling intervals, which puts greater loads on the fan clutch and shortens life. He also said under-the-hood inspections should focus on air leaks and loose or under-tensioned belts, which can slip. Drivers should be on the lookout for both when doing their pre-trips.
Ken Bridges from Gates Rubber Co. said a good belt drive system, properly maintained, should give 60,000-mile V-belt life and 150,000 miles for the new V-ribbed belts. Automatic belt tensioners should go for 350,000 miles. Maintaining factory-recommended belt tensions is critical, as is proper belt alignment, especially on ribbed drives. Belt tensioners should be checked regularly to see if they spin free and are wobble-free. A properly-maintained belt drive system should be noise and vibration-free.
Gene Wantuck from Borg Warner Cooling Systems said with viscous fan drives, it's important to make sure drives aren't permanently locked up or freewheeling. Any signs of bluing indicates excessive heat.
