Turbocharger – description and inspection

Description

1. A turbocharger improves engine power, lowers the density of exhaust smoke, improves fuel economy, reduces engine noise and lessens the effects of lower den­sity air at higher altitude. The turbocharger uses an exhaust gas-driven turbine to pres­surize the air entering the combustion cham­bers.

2. The amount of boost (intake manifold pressure) is controlled by a wastegate (exhaust bypass valve). The wastegate is operated by a spring-loaded actuator assembly, which con­trols the boost by allowing a certain amount of exhaust gas to bypass the turbine.

3. Turbocharged models are equipped with an intercooler – a heat exchanger through which the compressed air intake charge is routed to lower its temperature. Cooler air is denser, which promotes combustion effi­ciency, increasing power and reducing emis­sions.

Inspection

4. Though it’s a relatively simple device, the turbocharger is a precision component. Special tools are needed to disassemble and overhaul a turbocharger, so servicing should be left to a dealer service depart­ment. However, you can inspect some things yourself, such as a cracked turbo mounting flange, a blocked or restricted oil supply line, a worn out or overheated tur­bine/compressor shaft bearing or a defec­tive wastegate actuator.

5. A turbocharger has its own distinctive sound, so a change in the quality or the quan­tity of noise can be a sign of potential prob­lems. But before assuming that a funny sound is caused by a defective turbocharger, inspect the exhaust manifold for cracks and loose connections. For example, a high-pitched or whistling sound might indicate an intake air or exhaust gas leak. Inspect the turbocharger mounting flange at the exhaust manifold and make sure that the hose clamp that attaches the air intake duct to the turbo­charger is tight.

6. If an unusual sound is coming from the turbocharger, turn off the engine and allow it to cool completely. Remove the intake duct between the air cleaner housing and the turbocharger. Turn the compressor wheel to make sure it spins freely. Warning: The tur­bine or compressor wheels have very sharp blades; do not turn the blades with your fin­gers. Use a plastic pen. If it doesn’t, it’s pos­sible the turbo lubricating oil has sludged or coked-up from overheating. Push in on the turbine wheel and check for binding. The turbine should rotate freely with no binding or rubbing on the housing. If it does the tur­bine or compressor shaft bearing is worn out. Warning: Inspect the turbocharger with the engine off and cool to the touch.

7. The turbocharger is lubricated by engine oil that has been pressurized, cooled and filtered. Oil is delivered to the turbocharger by a supply line that’s tapped into the oil filter head. Oil travels to the tur­bocharger’s bearing housing, where it lubri­cates the shaft and bearings. A return pipe at the bottom of the turbocharger routes the engine oil back to the crankcase. Because the turbine and compressor wheels spin at speeds up to 140,000 rpm, severe damage can result from the interruption or contami­nation of the oil supply to the turbocharger bearings. Look for leaks in the oil supply line (the one on top). If a fitting is leaking, tighten it and note whether the leak stops. If the supply line itself is leaking, replace it. Remove the oil return line (on the bottom) and inspect it for obstructions. A blocked return line can cause a loss of oil through the turbocharger seals. Burned oil on the turbine housing is a sign of a blocked return line.

Caution: Whenever a major engine bearing such as a main, connecting rod or camshaft bearing is replaced, flush the turbocharger oil passages with clean oil.