I Just Fitted My Turbocharger & it's Still Blowing Smoke, Why?
Probably the most frequent question I've been asked over many years and more often than not by mechanics because in fairness they may rarely repair a turbocharged vehicle.
Unfortunately in most cases where mechanics aren’t familiar with turbocharged vehicles, analysis is limited to the obvious; "the turbo is leaking oil so it must be the turbo!” The dilemma being although the turbo is indeed leaking oil & blowing smoke again it is usually due to "the same vehicle fault" which caused it initially to be damaged &/or leak or a new installation fault has been introduced when fitting the turbocharger.
If you don't resolve the actual primary source of the problem you will be back to where you started, oil leakage from the turbo and/or blue smoke after you have replaced it coupled with total frustration as to what to do next. I'm sure most mechanic's initial response is, "I'm going to terminate the dude who rebuilt this turbo!”, and have tried.
I've spent many hours, months, years on the phone going through a check list of tests due to the turbocharger being the most misunderstood, victimised and cursed component on any vehicle when in fact it is one of the most reliable. Most of the tests listed below won't be found in any workshop manual as turbo fault diagnosis is not taught at trade school, it’s learnt from experience, theorised during many a sleepless night, and tested over the years. In most cases, one of the tests below will find the cause of your smoke quandary unless it falls under the category, “other possibilities”.
The New Seals Must be Faulty?
Briefly, turbochargers use piston ring seals1 on both the compressor & turbine & when installed there is a specified minimum / maximum measurable installed gap2 as per the turbo manufacturer's specifications to allow for expansion caused by heat. In addition to the seals the machining design to the rear of the turbine wheel shaft3 & front collars on the compressor side are intended to throw any oil in the vicinity of the seals back towards the centre of the bearing housing as it spins, loosely termed as an "oil slinger".
If there is fault causing oil to be forced or build-up against these piston ring seals they will indeed leak as technically their not oil seals, their primary purpose is to prevent boost on the inlet side & pressurised exhaust gas on the turbine side from entering into the bearing housing, the reversal of what is commonly presumed.
Technically a turbocharger fitted on a good engine with correct oil pressure, adequate oil drain and well designed breather systems etcetera, could operate with no seals installed at all and would not leak.
Pressurised oil enters the bearing housing and stabilises the turbine shaft. After the oil passes through the bearings it falls into a cavity at the bottom of the bearing housing making it's way back to the sump via an oil drain system, the flow rate back to the sump is governed solely by gravity.
A common remark I hear from many customers; "My turbo is leaking oil, the seals must be faulty" is not in likely whatsoever & in fact 99% of the time the fault is something other than the turbocharger.
The image to the left displays the manner in which oil flows to the turbocharger from the engine via the oil supply where the oil is under engine oil pressure then returns to the sump with gravity, it is then scavenged up by the oil pump and the cycle keeps repeating itself whilst the engine is running. (Engines & turbochargers vary in design from the image shown but the principle is the same for most!)