A turbo with bad bearings will leak oil out through the bearings into the intake or exhaust. If your car emits blue smoke from the tailpipe, check your turbocharger bearings. To check the bearings, remove the rubber intake hose from the compressor section of the turbo. Reach in with your fingers (uh, make sure the car is turned off and has cooled) to wiggle the compressor impeller. That's the fan-shaped thing. The impeller should spin freely, with no back and forth or side-to-side play. If it scrapes, wiggles in and out, or or doesn't spin, you'll need to replace the turbo.