Under Pressure, Part 2June 6, 2018
Turbocharger service tips
An engine that was factory designed for forced induction considers the turbocharger a main component much like a crankshaft. It is meant to last the life of the engine if given the proper maintenance. This is not to say that there cannot be a failure. In 90% of the cases it can be traced back to either poor maintenance or ingestion of a foreign object.
To properly care for a turbocharger is simple. It is sensitive to engine oil changes and the integrity of the intake/exhaust track. If a foreign object enters either the compressor or turbine housing, at the least the turbo will be damaged, and most likely destroyed.
Keep in mind that at a plugged air filter will cause an excessive pressure drop and a vacuum at the compressor oil seal that over time will challenge it and allow it to start pulling engine oil. Routine air filter service goes a long way to prevent seal wear along with a high-quality filter that has the proper flow rate.
Let the engine idle for a minute or so after being run hard. This lets the turbo slow down and for heat to be removed. This is an old procedure that is often neglected today but pays dividends over the life of the equipment.
Each brand and application will have unique diagnostic steps so please use this as a guideline. It is not meant to supersede a factory manual.
It is always wise to know your equipment. Does one engine on your farm use a wastegate to control boost while another employ’s movable vane? Though all turbochargers work under the same theory, the type of subsystem will deem the diagnostic and maintenance steps that are required.
The most common problems related to turbochargers are either a lack of engine power or exhaust smoke from oil consumption or if applicable, the ingestion of coolant from a water-cooled bearing housing.
When dealing with a lack of power the health of the engine needs to be confirmed first. Many blame a turbocharger for an engine issue. If the engine runs well, idles smoothly and sounds good, then there is an excellent chance the lost power or smoke is from the turbocharger system.
Never discount the diagnostic and preventative value of looking something over. Check all inlet connections from the turbocharger to the engine for a tight fit —- any loose hose clamps or compromised hoses will let boost escape.
Look for telltale signs of an exhaust leak prior to the turbine housing. This too will limit performance since not all of the exhaust gas will be going to the turbine.
Do not forget that the integrity of the intercooler (CAC) is extremely important. It is possible for it to get a crack in a tank or a small pin-hole in a tube, especially with a road vehicle. It may be necessary to remove the CAC and pressure check it as you would a radiator. If smoke test machine is excellent for this and will eliminate the labor to remove the CAC. If an oil seal goes bad on the compressor side it will put lubricant into the CAC. It will need to be washed out since not only will it cause exhaust smoke but will limit the thermal conductivity of the cooler.
If a wastegate is employed confirm that it is closed and not stuck open when chasing a lack or power or the engine is slow to build boost. Check the integrity of the line that goes to the diaphragm that senses boost. If it is cracked or leaking the engine will over boost. With a variable vane design, often carbon will build-up and stick the vanes or the solenoid that operates it will fail.
If a bearing or seal fails the integrity of the oil feed line needs to be confirmed along with that of the drain back. If the drain is clogged with sludge the oil will build up in the shaft housing and work through the seal.
On most engines the compressor inlet is easily accessible. Check the impeller for damaged or bent fins, excessive oil film and movement of the shaft. Keep in mind that with a floating bearing the shaft will move up and down slightly but if the fins hit the housing, it is excessively worn. A very slight film of oil is considered normal since under certain conditions it is sucked past the seal.
If and when the time comes that the turbocharger needs professional service it is important to make sure that the job is done properly. Failure analysis is the first step — the reason for the breakdown needs to be identified.
Original equipment quality seals and bearings should be used and the assembly should be balanced after it is repaired. This requires special equipment that a low-dollar rebuilder will not have or if you ask them will say is not necessary. A properly balanced turbocharger will perform as intended and will last. This is an imperative step that is often skipped.