Turbo heart attack risk—watch out for constricted feed line
The effects of aging and heat cause coke deposits in the infeed and throttle the flow rate to the turbocharger. Eventually, this minimal lubrication is no longer enough—the bearings start to seize up.
Flexible oil lines, especially, will become kinked sooner or later. This plastic deformation can never be restored to its correct shape. Here again, this causes bottlenecks in the supply line.
Liquid sealants are an absolute no-go for turbo repairs. They can clog the infeed and block the fine oil holes in the bearing housing. Anyone who uses this sort of sealant for installation must have sprung a leak themselves!
Loss of pressure is deadly to turbochargers
Like the crankshaft, the pistons, the hydraulic followers, etc., the turbocharger needs a certain oil pressure. It can only work properly with engine oil that is under pressure. A lubricating film forms between the shaft and the plain bearings, on which the shaft basically “floats.” There is essentially no wear because the two parts of the bearing do not make contact with each other. Failures in the oil supply make themselves known in the turbocharger first, because it is the weakest link in the oil circuit. Other bearing points are not under as much load and especially are sized much larger. If the oil pressure fails under full load, it takes only a fraction of a second for the turbocharger to blow out. The most common causes are defective oil pumps and blocked control valves, which adjust the oil pressure to the engine speed ( see TM 04/2016).
A “sick” environment damages the “healthiest” turbo
Lack of lubrication can occur even with a clear oil feeder line and perfect oil quality. Namely, if there are problems in the engine environment of the turbo, for example, if a diesel particulate filter (DPF) becomes clogged. Because the saturated DPF generates such high back pressure, the exhaust gases no longer flow freely out of the engine into the DPF. As a result, they seek the path of least resistance—which is through the turbine side of the turbocharger and back to the oil pan. On the way, they pass through the turbine-side radial bearing and force out the vital oil film. This causes inadequate lubrication, the bearing components make contact, and the shaft starts to seize and ultimately locks up. (More information here: “When the turbo won’t charge” and TM 03/2016)
Dangerous for turbochargers: bad oil
Oil quality plays a crucial role today. Especially in modern diesel engines, special additives are required. Without these additives, expensive engine damage can occur. Cleaning additives are also added to the oil. They prevent oil carbon and other residues from accumulating, or break them down. The turbocharger is the first to suffer from any scrimping here. Low-quality or old oil can cause increased oil carbon buildup. These residues then act like abrasives on the radial bearings of the turbocharger—wear increases tremendously.