Hotter Under The Hood
Today's EGR engines crank out a lot more underhood heat, and there's nowhere for it to go.
Jim Winsor
Executive Editor
One of the hottest topics in the industry these days (pun intended) is the impact of higher underhood temperatures brought about by many of the post-'02 low emission engines used in today's trucks.
Much of this temperature increase is driven by all the EGR (exhaust gas recirculation) hardware packed onto engines. The cooling system has to handle a lot more heat, and there are air-flow problems that are only compounded by tighter engine compartments - especially with aerodynamic hood configurations. As a result, there's no easy route for all that hot air to escape.
These issues were the subject of an interesting technical panel at February's Technology and Maintenance Council (TMC) meeting in Tampa, which I had the pleasure of moderating.
What problems do these high underhood temperatures cause? In some cases they're shortening fan clutch life and cooking coolant hoses and fuel lines. They're also affecting power steering pump seals because power steering oil temps are significantly elevated. Alternator manufacturers now offer high-temp models to gain back longer life. You can buy them as replacements or make sure to spec them on new vehicles. And there now are upgraded fan drives to better deal with heat.
Participants were shown silicone hoses - parts that should last the life of a vehicle - that had deteriorated from the inside out in just a few years. Automatic belt tensioners used with today's serpentine belts are smack dab in the engine's hot air flow and are susceptible to shortened life caused by the heat's effect on tensioner bearings and lubricants. Belts themselves also suffer from the hotter engine environments.
While engine coolant temperatures are only slightly increased - in the 200-plus F range - it's the higher volumes of hot air blasted back over and around the engine and finding no easy exit that's "cooking" everything.
Best overall advice the panelists had to offer is to make sure service technicians thoroughly examine all hoses and belts during each vehicle PM service. Also, spin belt tensioners and listen for bearing noise. Catch potential problems in the shop and prevent road failures.
The "hot" side of engines - around and under turbos - are said to be the worst areas, especially where EGR coolers are located. Some fleets have been adding sleeves and/or shielding to block heat. Others are replacing plastic air governor lines with stainless steel braided hoses with Teflon inner liners. Even windshield washer reservoir bottles have been shielded on some models.
How hot is "hot?" Ron Szapacs, maintenance manager for the Air Products and Chemicals fleet near Allentown, Pa., took temperatures with thermometers strapped at various locations under the hood on one popular 2005-model tractor in his fleet. While these figures are representative only of this model, they are examples of what the high-temperature issues are. The readings below were taken last September when the ambient temperature was only 78 degrees F. Engine coolant was between 200 and 210 degrees F. Recordings were taken shortly after the loaded rig had pulled a long grade.
• Front of power steering reservoir - 225-251 F.
• Firewall temperature above and behind the rear cylinder head on turbo side of engine - 220-250 F.
• Temperature probe in upper half of windshield washer reservoir - 140-145 F.
• Engine hood fender temperature at plastic dirt shield, right side - 129 F.
• Firewall at driver's side by steering column near top of cowl by air governor - 142 F.
What are some fleets doing to reduce temperatures? Mainly trying to improve air flow under the hood by getting more air in and out. One way is by adding vents and even a hood scoop. Vents that get the air out faster seem to get the best results. Several fleets reported removing the inner fender shield skirts to open up areas for air to exit.
Vehicle manufacturers reportedly are upgrading both cooling system capacities and air handling under the hood on new models. In the meantime, if your fleet is having short belt, hose, fan drive and belt idler life, you might want to try some of the "fixes" outlined here.
