Waste gate valve. If the turbocharged air pressure becomes too high, knocking occurs and engine output actually decreases. To prevent this, the turbocharger uses a waste gate valve. This valve allows a certain amount of exhaust gas to bypass the turbine once the ideal boost is exceeded. The waste gate is usually operated by an actuator that senses the air pressure in the induction system. When the pressure becomes too high, the actuator opens the waste gate valve. The flow of exhaust gas reaching the turbine decreases. This reduces turbine and compressor wheel speed. The result is a drop in turbocharged air pressure.

Intercooler. The intercooler cools the turbocharged air before it reaches the combustion chamber. Cooling the air makes it denser. It also lower the temperature produced in the combustion chamber. These factors help reduce engine knock and increase engine output. Intercoolers are like radiators in that heat from the air passing through them is removed and dissipated to the atmosphere. Intercoolers can be air or water cooled.

Lubricating system. Most turbochargers are lubricated by pressurized and filtered engine oil that is line-fed to the unit¡¯s oil inlet. The oil drains back to the engine (by gravity) through a separate line. The  lubrication system is critical to the center bearing of a turbocharger. This bearing has the high heat of the exhaust on one side of it and the oil tends to keep it cool as well as lubricate it.

A turbocharger should never be operated under load if the engine has less than 30 psi oil pressure. A turbocharger is much more sensitive to a limited oil supply than an engine, due to the high rotational speed of the shaft and the relatively small area of the bearing surfaces. Low oil pressure and slow oil delivery during engine starting can destroy the bearings in a turbocharger. During normal engine starting, this should not be a problem. There are, of course, abnormal starting conditions. Oil lag conditions will most often occur during the first engine start after an engine oil and filter change. Before the engine is put under load and the turbo activated, the engine should be run for 3 to 5 minutes at idle to prevent oil starvation to the turbo. Similar conditions can also exist if an engine has not been operated for a long period of time. Engine lube systems have a tendency to bleed down. Before allowing the engine to start, the engine should be cranked over until a steady oil pressure reading is observed. This is called priming the lubricating system. The same starting procedure should be followed in cold weather. The thick engine oil will take a longer period of time to flow.