What a turbo does and how to look after one
Turbochargers are now common in both diesel and petrol cars. They let a small engine pull like a bigger one, often with lower fuel use when driven gently. They also add parts that need care, so it is worth knowing what a turbo is, how it can fail and what to check on a used car.
The idea in one paragraph
An engine makes power by burning fuel and air. The more air you can pack in, the more fuel can be burnt, and the more power you get. A turbo is an air pump driven by the exhaust gas that would otherwise be wasted. Hot gas spins a small turbine, the turbine spins a compressor on the same shaft, and the compressor pushes extra air into the engine.
Main parts
- Turbine and compressor: two small wheels on one shaft, spinning at very high speed.
- Oil feed: engine oil lubricates and cools the shaft. This is why clean oil is so important.
- Intercooler: compressed air gets hot, and hot air is less dense. An intercooler cools it before it enters the engine.
- Control valves and electronics: they limit the boost so the engine is not overloaded.
What it feels like
Turbo engines often feel strong at low and middle speeds, which makes everyday driving relaxed. A short delay between pressing the pedal and the surge of power is called turbo lag, and modern designs have reduced it a lot. Some turbo engines are tuned for economy, others for performance, so the label alone does not tell you what the car is like.
Why turbos fail
Most turbo problems trace back to oil and heat.
- Dirty, old or wrong oil starves the shaft bearings.
- Stopping the engine straight after hard driving can leave the turbo hot without oil flow, which can bake the oil in its channels.
- Blocked or leaking oil lines reduce lubrication.
- Foreign objects or dirt entering through a damaged air path can damage the fast-spinning wheels.
- Faults elsewhere, such as a leaking intake hose or a sticking control valve, can make a healthy turbo look faulty.
Habits that help
- Change the oil and filter on schedule with the grade the maker recommends; see engine oil explained and how often to service.
- Let the engine warm up by driving gently for the first few minutes. Avoid full power while it is cold.
- After a long, hard drive, such as a fast motorway run or towing, let the engine idle briefly or drive the last stretch calmly before switching off. Follow the guidance in your manual, since modern designs vary.
- Keep the air filter clean; see air and cabin filters.
- Do not ignore warning lights or a sudden loss of power.
Signs of trouble
- A whistling, siren-like or grinding noise that is new or louder than before.
- Loss of power, especially when accelerating.
- Blue or grey smoke from the exhaust, or oil consumption that has risen.
- Engine warning light or limp mode, in which the car limits its own power.
These symptoms can have causes other than the turbo itself, so a proper diagnosis is better than guessing. A turbo replacement can be a significant repair, which is why you should check carefully before buying.
Buying a used turbo car
Ask for proof of regular oil changes; it is the single most revealing record. On the test drive the car should pull cleanly without hesitation, whistles or smoke. Check for oil residue around the intake hoses and the intercooler, and look at the oil on the dipstick or filler cap in line with the guidance in our inspection guide. Be careful with a car that seems to have been tuned for extra power; extra boost raises the load on every part.
Is a turbo right for you?
If you mostly do short trips in cold weather, a turbo adds more to look after than a simple naturally aspirated engine. If you do mixed driving and keep up with servicing, it is a good technology. Compare your options in diesel or petrol.
What to remember
- A turbo uses exhaust gas to push more air into the engine.
- Clean oil and gentle warm-ups are the best protection.
- New whistling, smoke or loss of power needs a proper diagnosis.
- A service history is the best evidence when buying used.
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