The life of turbos depends on turbo bearing lubrication. If a non water-cooled turbo gets red hot, which it can do on a motorway, on a long ascent, or while towing, then it must be left to idle for a few minutes before switching off so oil continues to circulate through the
bearing, lubricating it and cooling it. A few miles driving relatively
slowly at the end of a journey, for example through a town, does the same job. Switch off a red hot turbo and the oil in the bearing carbonises while the vanes continue to spool down so the turbo is spinning on its bearing with no lubrication. This most commonly happens when stopping for fuel at a motorway service station. If the turbo bearing oil seals fail on a diesel engine this can result in sump oil being sucked up through the turbo and the engine running uncontrollably on its sump oil. It can also fill the intercooler with oil. A common mistake is to replace a turbo because of oil seal failure and not either clean out or replace the intercooler, after which the replacement turbo will have a very short life.