TURBOKILLERS

IT IS A COMMON MISTAKE TO VIEW A TURBOCHARGER AS AN ADD-ON COMPONENT TO AN ENGINE, LIKE YOU WOULD AN ALTERNATOR. THEREFORE, THE ASSUMPTION IS, WHEN IT FAILS, IT IS THE TURBO’S FAULT AND A NEW UNIT IS NEEDED. AS THE TURBO IS SUCH AN INTEGRAL PART OF AN ENG

1 LACK OF LUBRICATION

The number one killer is a lack of lubrication. Owing to the fact a turbo can spin quicker than 200 000 r/min means the boundarylayer lubrication at the bearings is critical. If for some reason the correct-speci cation oil does not reach these areas at the correct pressure, turbo failure is imminent. Lubrication problems may include incorrect oil, faulty oil pumps and a blocked oil feed (or drain) pipe. When a turbo is replaced, a dry start-up – if the correct lubrication procedures were not followed – can kill a turbo in a matter of seconds. Even at idle, the turbo spins at about 10 000 r/min.

2 OIL CONTAMINATION

It is not just suf cient for the turbo to receive oil; the liquid also needs to be clean. As the turboshaft spins at such high rotational speeds in the bearings, any particles or debris in the oil act as grinding paste and wear away the shaft and brass bearings in the case of the journal type. Forensic analysis of this failure mode reveals scoring on the shaft and bearing surfaces. The wear can result in bearing failure and seizure but will initially lead to other problems.

3 EXCEPTIONAL OPERATING CONDITIONS

If a turbo runs outside its design envelope, failure can be catastrophic. This includes over-speeding of the turbo leading to burst compressor and turbine wheels if, for example, there is a problem with the wastegate control (or variable-nozzle turbo actuator). The turbo materials are designed for a speci c temperature range; exceeding this is terminal. Hot shutdown is a known killer because oil starts coking to bearing surfaces. Although modern watercooled turbos with electric water pumps are designed to cope with engine stop/ start systems, Chris Kambouris feels there’s merit in letting a turbo cool down by allowing the engine to idle after sustained hard driving.

4 FOREIGN OBJECT DAMAGE

Imagine throwing a rock into the blades of a room fan. The result is similar to a foreign object entering a turbocharger but the damage is ampli ed because of the elevated speeds. Run the vehicle without an air lter and the dust particles will sand-blast the compressor blades. On the turbine side, any debris the engine coughs out can be lethal. Even the sealant wrongly applied by some turbo installers on the turbine ange can harden and break off in tiny pieces, ripping the blades to shards.