I just fitted the turbo & it's still blowing smoke!
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, analytics is limited to, "the turbo is leaking oil so it must be the turbo!” The dilemma is although the turbo was indeed leaking oil it is usually due to some other factor causing it to leak or inflict damage to it. Don't resolve the actual primary source of the problem and 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 exterminate the dude who rebuilt this turbo!”
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”.
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What's a Piston Ring Seal Anyway?
Briefly, most turbochargers use piston ring seals1 & when installed there is a specified minimum / maximum measureable installed gap2 as per the turbo manufacturer's specifications to allow for expansion caused by heat. In addition to the seals the machining design on the rear of the turbine wheel shaft3 & front collars 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 & exhaust gases 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 statement I hear from many customers; "My turbo must have faulty seals" is not in fact a realistic possibility.
Turbocharger Lubrication System:
The following image displays the manner in which oil flows to the turbocharger from the engine oil supply under 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 vary from the below image but the principle is the same for most!)
Checklist:
- Allow time for any oil residue in the inlet or exhaust to burn away.
- Remove the oil filler cap & check for fumes.
- Check the oil level.
- Check the air filter, intake pipes, clamps.
- Check the breather hoses, (filter and canister if fitted).
- Spark plug test.
- Check the oil quality, type, was it changed?
- Check the oil drain for any restrictions.
- Sump pressure test via removal of oil drain.
- Sump pressure test under boost conditions.
- Compression and leak-down test.
- Check oil flow &/or pressure at idle and high rpm.
- Other possibilities.
- The turbocharger.
Details:
2. Valve cover smoke test:
2. Valve cover smoke test:
Very simple yet very reliable provided the engine oil isn't well overdue for an oil change and lost all of its viscosity. While the engine is running at operating temperature, with rag in hand, undo the oil filler cap carefully so as to not get splashed with oil. It is best to tilt your head level with the valve cover and check if there are any signs of visible fumes being emitted whilst giving the engine a few light revs. You may feel some pressure which is usually normal on some vehicles but no signs of fumes or smoke whatsoever which is generally the signature of engine blow-by which is oil making its way into the combustion chamber, partially burning then returning back as smoke out through the open oil filler via the timing cover.
Blow-by will cause pressure in the sump restricting the oil being returned from the turbocharger, a bit like putting your thumb over the oil drain pipe. Oil enters the turbo under engine oil pressure; however after it has left the turbo bearings there is no oil pressure at all on its journey back to the sump. If there is any sump pressure, no matter how minuscule, it will prevent oil returning to the sump and force it out of the turbo through the piston ring seal(s).
Pressure in the sump increases as boost increases & the smoke from the valve cover also increases but you can only test this under boost with the aid of a chassis dyno although having said that I have to admit I have tested vehicles on the road by installing a very long breather hose into the passenger side window. Anyway on the dyno under full boost it is better to remove the breather hose to try and view any fumes rather than the oil filler cap to avoid oil being splashed around the engine bay.
4. Blocked air filter or intake pipe(s) / intake hose(s):
4. Blocked air filter or intake pipe(s) / intake hose(s):
Any restriction at the intake side of an engine such as a heavily clogged air filter will result in oil leaking from the inlet side of the turbo. The compressor wheel, whilst spinning to generate boost will attempt to source large volumes of air from wherever possible, if it cannot acquire enough air via the intake system, it will tend to pull oil from within itself through the front piston ring seal.
It may also drag oil from the breather hose pending its location.
If there is a severe blockage it may also cause thrust bearing wear allowing excessive end-float from a pressure imbalance leading to a severe turbocharger failure.
I have seen "soft" intake hoses collapsing under higher RPM as the inner walls of the hose pull inwards, touch and act as a seal.
If leaking oil puddles in the bottom of the compressor cover to the point where the compressor wheel blades are "scooping" oil, it will tend to pull the compressor wheel downwards wearing the bearings and other turbo components, again causing severe turbocharger failure.
Should there be a leak in the air cleaner assembly, split hose or loose pipe due to an unfastened clip or clamp, dust will be drawn into the intake system, damage the compressor wheel and score the cylinder bores of the engine requiring both an engine and turbocharger rebuild.
5. Blocked or kinked breather hose(s), blocked PCV valve:
5. Blocked or kinked breather hose(s), blocked PCV valve:
All engines must breathe as the action of the pistons travelling up and down act as an inverted air compressor on the sump side of the pistons which must be vented. Check the breather connections aren't blocked, hose's are not kinked or softened and any breather filter, canister or air filter assembly is free from oil, dust, dirt or debris. Breather system designs vary from vehicle to vehicle but the principle of removing pressure is a common denominator.
On many “extreme” race vehicles it’s common for a vacuum pump to be fitted to the lower part of the engine block or upper sump area, pumping and directing any pressure generally into the exhaust system.
A regular customer popped in with his twin turbo Toyota Soarer emitting smoke profusely from the exhaust system. He had fitted a "high performance catch-can" with an oil bleeder to his vehicle the night before and presumed he had installed it incorrectly. We checked the vehicle on the chassis dyno and sure enough clouds of smoke were bucketing out of the exhaust. It didn't take long at all to diagnose the problem; the original Soarer breather hose is 1 inch in diameter and the catch-can kit was fitted in line with the original, as per the instructions. We discovered the 1” hose entering the catch-can and a 5/16 of an inch fitting and hose exiting it thus the engine couldn't breathe properly, sump pressure was introduced because of the design of the catch-can and consequently oil leaked from both piston ring seals of the turbocharger resulting in smoke.
We had a flood a phone calls shortly thereafter by Soarer owners with the same problem due to the breather kit being promoted as a “must have “on the Soarer Club forums. We just quickly explained how to solve their problem over the phone and the problem soon went away.
8. Oil drain restriction: silastic, kinked hose, carbonised pipes:
8. Oil drain restriction: silastic, kinked hose, carbonised pipes:
Many a turbo will leak oil or fail due to carbonisation caused by lack of oil changes and/or repeated hot shut downs which I will cover in more detail elsewhere since carbon build-up in the turbo is removed during the reconditioning process and not related to installation. However if the turbocharger was heavily carbonised it's very likely the oil supply and oil drain pipes were also carbonised, some totally. What is carbon? Think of it as lethal, heat treated, hardened, black kryptonite which if not completely removed will destroy your turbocharger. It may be relatively easy, very difficult , or virtually impossible to remove pending how long the lack of maintenance and/or hot shuts downs continued for.
Soaking in a cold or hot acidic* bath over night, preferably sonic, should soften the carbon although sometimes it only softens a small amount at each end in extreme cases. Digging with wire, tapping with a dolly, applying heat, drilling, an industrial jack hammer or TNT may also assist. The oil feed pipe can sometimes be near impossible to clean properly if at all as they are smaller in diameter, around 1/4" in most cases and can be long with many bends. The oil supply is probably best replaced in most cases. Oil drain pipes generally are much larger in diameter and a tad easier to clean but not always. Anyway the point is both pipes have to be completely cleaned or replaced with no doubt of cleanliness attached whatsoever!!!
Be cautious of some vehicles, particular some front wheel drives, where the vehicle manufacturer, not caring or not knowing, ran the oil supply pipe directly along the top of the exhaust manifold to insure carbonisation occurs, In these cases the turbo maybe fairly clear of carbon but destroyed due to no oil yet the oil supply pipe maybe partially or totally blocked. Fit a new turbo without cleaning the pipe and the new turbo will fail immediately.
*DO NOT fool around with acid unless you follow all the safety precautions, have all the required protective clothing, proper ventilation, stored in a safe place etc. In fact it’s best left to professionals.
10. Sump pressure test under boost conditions:
10. Sump pressure test under boost conditions:
This test is best conducted on a chasis dyno but can also be conducted on the road with a passenger. Using a good quality vacuum hose, slip it over & cable tie it to the dip-stick tube, (remove dip-stick first :) ). Insert the other end onto a good quality, vacuum / pressure gauge which displays small increments of pressure and vacuum. Run the car up on the dyno, or if on the road, pass the gauge through a gap in the bonnet then through the passenger window. Obtain full boost whilst watching the gauge and the indicator arm should never travel into the positive side of zero. Any reading, no matter how small above zero will point to sump pressure causing the turbo to leak oil.
*Insure the oil drain pipe/hose in properly connected when using this method as a test!
12. Too much or not enough oil pressure / flow:
12. Too much or not enough oil pressure / flow:
Not very common and occurs mainly due to lack of maintenance in the case of a sticky oil pressure relief valve or as a result of high pressure oil pumps in race applications. More pressure, more volume; too much oil will flood the bearing housing as it can't drain quick enough back into the sump and consequently oil will leak from the turbo piston ring seal(s). Obviously removal and cleaning or replacing the oil pump relief valve should solve that problem. Conversely not enough oil pressure will cause a turbo to self destruct rather than leak. Oil pressure can be lost elsewhere in an engine for any number of reasons causing low oil pressure at the turbo as well. Too test whether there is too much or not enough oil flow follow the directions in bold below.
In the case of the race engine where the owner requires higher oil pressure for other reasons a restrictor can be placed in the line to the turbo however this must be done with much care as not enough oil will obviously cause the turbo to fail in a major way. In order to fit a restrictor you first need to source the required information; "the flow per minute of oil for the turbocharger from the turbo manufacturer and measure this amount out of the turbo oil drain pipe". Start with larger inside diameter restrictors and gradually decrease in size until you find the correct size restrictor that meets the turbo manufacturers specifications at the correct given engine rpm.
If oil pressure needs to be checked it's best done at the oil entry to the turbocharger and will require a fitting to be made for the oil pressure gauge which will vary pending the brand of turbo.
