E&MU: Turbo Maintenance: Keep It Cool, Keep It Lubed

By Stephen Bennett, Contributing Writer

This story appears in the March/April 2013 issue of Equipment & Maintenance Update, a supplement to the March 18 print edition of Transport Topics. Click here to subscribe today.

Turbochargers are not typically a red-flag item on fleet maintenance agendas, but straying from routine service can set the stage for catastrophic failure, manufacturers and maintenance experts said. But close attention to some core areas — namely regular engine oil changes and the air intake system — can prevent damage to the turbocharger and other components.

“You don’t want any old oil running through that turbocharger,” said Gregg Hodgdon, head of fleet operations for Deli Express/E.A. Sween Co. of Eden Prairie, Minn. The company operates about 100 Isuzu NPR Eco-Max trucks with turbochargers in its fleet of about 350 trucks, he said.

“[Turbos] usually work fine as long as you keep up with the oil changes,” he said. Trucks in the Deli Express fleet get engine oil changed at 7,500-mile intervals. “The main thing is the bearings have got to have good lubrication,” he said.

Found on most modern diesel engines, turbochargers boost engine combustion by recycling the engine’s exhaust gas through a turbine and back into the cylinders. The turbine spins an impeller that receives filtered air, which is then compressed to about 14 pounds per square inch, said Bill Mohr, vice president of service operations for Mitsubishi Fuso Truck of America, Logan Township, N.J.

But that compression increases intake air temperatures to as much as 300 degrees Fahrenheit — causing the air to expand and lessening its oxygen level, Mohr said. The intake air must be cooled by passing through an intercooler, a radiator-like component designed to let the heat dissipate. (Other turbochargers are liquid-cooled.) As the intake air cools, it recovers density, increasing the level of oxygen available for combustion in the chamber of the engine and providing the power boost.

The largest percentage of turbocharger failures are caused by insufficient lubrication and by contaminants in the oil that keep those parts spinning, said Thom Miles, marketing manager for the North American aftermarket for BorgWarner Turbo Systems, Asheville, N.C. BorgWarner manufactures turbochargers for original equipment manufacturers and for the replacement market. Engine power loss, excessive smoke, excessive noise and the appearance of oil at either or both ends of the turbocharger may be signs of a failure, he said.

If engine oil loses viscosity or becomes dirty, “then you’ll start to see bearing wear in the turbocharger,” said Mike Rossetti, manager of technical services, Isuzu Commercial Truck of America, Anaheim, Calif.

Joe Korn, a certified ASE technician and consulting analyst with Automotive Resources International, Mount Laurel, N.J., a fleet management company, said dirty oil can contribute to “scaling of bearings and engine oil coking, which ultimately can lead to major failures.”

Operators should allow a cool-down period before shutting down the engine, said Zack Ellison, director of customer support for Cummins Inc., Columbus, Ind. Cummins is an engine maker with a subsidiary, Holset, that manufactures turbochargers.

“If a vehicle has been pulling a long, hard grade at full throttle, the engine should be allowed to idle for 15 to 30 seconds before being shut down,” Ellison said. That allows the turbo bearings to cool and helps to prevent damage caused by high temperatures, he noted.

Wayne Beal, service manager for Kenworth Sales Co., a dealer in Spokane, Wash., said, “If you just shut it off, there is the potential for parts seizing up.”

But effective turbo cooling requires more than just a few minutes of idle time.

Some turbochargers are cooled by engine coolant, said Mohr of Mitsubishi Fuso. “Coolant actually flows through the turbocharger” via lines from the engine block. This design provides an additional reason for attentive maintenance of the engine’s cooling system, Mohr said, including periodically checking fan belts and operation of the fan clutch, cleaning exterior radiator cooling fins and changing engine coolant according to manufacturers’ recommendations.

Keeping the air filter and intake system clean is also critical to the health of the turbo, experts said. Filtering removes dirt and dust that have potential to damage the turbocharger and the engine.

“The air filter is incredibly important,” said Rossetti of Isuzu. “If dirt passes through the air filter, it’ll damage the turbocharger. It’ll actually sandblast the impeller.”

After mechanics remove the air cleaner element, they should inspect to ensure that there have been no leaks in the paper filter, Ellison said.

After inspecting the paper filter, a mechanic should wipe out the filter housing with a damp cloth to remove dust, Ellison said by e-mail. Inspect the air piping system to be sure there are no leaks that could allow dirt to enter the intake system, he added. “Engines that have ingested dust will typically need a turbo replaced before the [fleet operator] realizes that dust has compromised the engine,” Ellison said.

While turbochargers on gasoline engines have typically been featured on performance automobiles, Ford Motor Co. has introduced a turbocharger on some of its gasoline-powered trucks. BorgWarner provides the turbochargers for the Ford EcoBoost engine in rear-wheel-drive applications such as the F-150 pickup truck, said Miles, the BorgWarner marketing manager.

Some engine experts said turbochargers could become more common on gasoline engines in the years ahead, in large measure because of the federal corporate average fuel economy mileage standards for new vehicles.

CAFE was enacted by Congress in 1975 to reduce energy consumption by increasing the fuel economy of cars and light trucks. The Obama administration in 2012 finalized CAFE standards equivalent to 54.5 miles per gallon for cars and light-duty trucks by model year 2025.

“In order to meet the increased fuel-economy standards required by future CAFE regulations, we believe that more light-duty trucks will [become] available with smaller displacement turbocharged engines,” said ARI’s Korn. He believes that most of the options would be on gasoline-fueled light-duty trucks “and that some small displacement diesel options will also be offered.”

Mohr said turbochargers “do the same for gasoline engines as they do for a diesel engine. They increase power because you have more efficient combustion, more oxygen available in the cylinder.”