A turbocharger takes energy your engine is already throwing away and turns it into power. A smaller engine can then perform like a bigger one while using less fuel. That's why turbos have moved from race cars and heavy diesels into almost every new bakkie, SUV and hatchback on South African roads.
Here's how they work, and what kills them.
The basic idea: more air, more power
An engine's power is limited by how much air it can pull into its cylinders. More air means more fuel can be burned, and more fuel burned means more power.
A naturally aspirated engine relies on atmospheric pressure to fill the cylinders. A turbocharger compresses the intake air, so each intake stroke packs in a denser charge. This is called forced induction.
How it works
A turbo has two wheels on one shaft, each in its own housing:
- The turbine (hot side). Exhaust gas leaves the engine at several hundred degrees Celsius, and on petrol engines it can go well over 900°C. It flows through the turbine housing and spins the turbine wheel.
- The compressor (cold side). The compressor wheel sits on the same shaft, so it spins at the same speed. It draws in fresh air, compresses it and sends it to the engine.
The shaft turns at well over 100,000 rpm, and small turbos run past 200,000 rpm. It rides on bearings that are lubricated and cooled by engine oil. Keep that in mind, because it's the key to why turbos fail.
In sequence:
- Exhaust gas leaves the cylinders and enters the turbine housing.
- The gas spins the turbine wheel, then exits through the exhaust system.
- The shaft drives the compressor wheel.
- The compressor pressurises the intake air. This pressure is called boost.
- The pressurised air passes through the intercooler and into the engine.
- The denser air charge lets the engine burn more fuel efficiently and make more power.
How it works
If nothing limited it, a turbo would keep spinning faster as exhaust flow rises until it overboosted the engine or destroyed itself. Two main systems keep it in check:
- Wastegate. A valve that sends some exhaust gas around the turbine once the target boost is reached. It's common on petrol engines and older diesels.
- Variable geometry turbo (VGT/VNT). Adjustable vanes in the turbine housing change how the exhaust gas hits the wheel. This gives strong boost at low revs and controlled boost at high revs. It's standard on most modern diesels, and carbon build-up on the vanes is a common cause of sticking and limp mode.
Why the intercooler matters
Compressing air heats it, and hot air is less dense. That cancels out part of the benefit of boosting it. The intercooler is a radiator for the intake air. It cools the charge before it reaches the engine, which gives more power, lowers the risk of knock and reduces strain on the engine.
Turbo lag
A turbo needs exhaust flow to spin up, so there's a short delay between pressing the accelerator and the boost arriving. Modern engines reduce this lag with smaller, lighter turbos, VGTs and twin-turbo setups. On a healthy modern engine you'll hardly notice it.
Why turbos fail
Most turbo failures aren't caused by the turbo. They're caused by something else on the engine. The usual causes:
- Oil starvation. A blocked or kinked oil feed line, low oil level or a worn oil pump. The bearings fail within seconds.
- Contaminated or degraded oil. Long service intervals, the wrong oil grade or sludge wear the bearings and shaft.
- Foreign object damage. A torn air filter, a loose intake hose or engine debris chips the compressor or turbine blades.
- Hot shutdowns. Switching off straight after hard driving or towing stops the oil flow while the turbo is still extremely hot. The oil cokes in the bearing housing.
- Excessive exhaust temperature or overboost. Often caused by tuning, a faulty boost control or a blocked DPF.
Fitting a new turbo without fixing the cause means it will fail again, often within weeks. When a turbo is replaced, the oil feed and return lines should be replaced or checked, the oil and filter changed, the air intake inspected and the root cause identified.
How to make a turbo last
- Service on time with the oil grade the manufacturer specifies.
- Let the engine idle for 30–60 seconds before switching off after hard driving or towing.
- Don't drive hard until the engine reaches operating temperature.
- Keep the air filter and intake system sealed and in good condition.
- Investigate warning signs early: whistling or siren noises, blue or black smoke, loss of power, oil in the intercooler pipes, or limp mode.
Need a turbo or turbo parts?
Turbo Diesel Components supplies turbochargers, cartridges (CHRAs) and turbo components for a wide range of passenger, commercial and industrial applications. Contact our team or search our catalogue to find the right part for your vehicle.