Many fleet managers I know have a love/hate relationship with the turbochargers so essential to modern diesel engine. The advantages of turbochargers in terms of increased power, torque and engine efficiency are obvious. The frustration of vehicle downtime and expensive repair bills due to blown turbochargers is the downside to the benefits they offer.
OEMs are striving continuously to make turbochargers more durable and reliable. But the inescapable truth is that turbos perform a tough job in a hellish environment. It’s a testament to modern engineering that they perform as well as they do.
But there are simple things your drivers can do to help extend turbocharger life and perhaps even dodge a breakdown or two along the way.
Jim Gambill, is DELO brand manager for Chevron, says the oil company has been conducting interviews with vocational fleets experiencing these problems and decided to do some research to see if it could identify some contributing factors to premature turbo failures. The results are pretty interesting.
Gambill says Chevron focused on fleets engaged in heavy urban applications for its research efforts – particularly vehicles running shorter routes in heavy, stop-and-go traffic. “Specifically, based on customer input, we were wondering about vehicle temperature increases once the engine was shut off and how that pertained to turbocharger failure and overall engine oil life,” Gambill told me. “And what we found was surprising.”
Chevron’s research found that diesel engine temperatures can rise as much as 70 degrees, Fahrenheit, after the vehicle ignition is switched off. Moreover, trucks stuck in stop-and-go traffic can see less dramatic engine temperature spikes of 18 degrees F because the engine is not being cooled efficiently. “For a healthy engine operating around 190 degrees F, those are significant increases,” Gambill notes. “But even more worrying is that fact that for every 18 degree F increase in engine temperature, the life of oil subjected to these hot spots decreases by half. While the bulk of the oil in the pan is OK, a certain percentage of the oil trapped in the turbocharger bearing and other upper engine components gets ‘cooked’ – that is it oxidizes; acids appear in the oil. These can cause acid etchings on engine components along with other deposits which can bind to internal surfaces leading to premature component failure.”
Luckily, there are some fairly easy steps fleets can take to head off some of these problems. The first, Gambill says, is to pay particular attention to your Total Acid Number (TAN) on any oil sample analysis you do. This will tell you if you oil is breaking down prematurely and can be a strong indicator that component wear is already occurring.
Another proactive step is to coach drivers to allow the turbochargers to idle down before shutting off an engine. “Everyone is in a hurry these days, so this can be a tough idea to introduce,” Gambill admits. “But basically, if your drivers will let an engine idle from 1 to 3 minutes before switching it off, it will allow the turbochargers to cool down and avoid the sharp temperature spikes seen with a hot engine shutoff. This will help increase oil and component life on the vehicle.”
Naturally, Gambill stresses using premium engine oils and coolants to give engine components a more robust defense against excessive heat, oxidation and deposits. He also suggests carefully reviewing drain intervals to make sure they are solidly aligned with the application at hand. “In many vocational applications, oil change intervals can be 30 percent less than those for long-haul fleets,” he notes. “In severe-duty roles, it can be up to 60 percent less. “
Gambill says Chevron is continuing to run tests on high engine temperatures and premature turbocharger failure and expects to have additional data soon. In the meantime, he says, having drivers take an extra minute or two to let engines idle down and keeping close tabs on oil health and change intervals could help many vocational fleets save time, money and frustration.