Turbo failure: symptoms and causes

A turbo uses exhaust gas to force extra air into the engine, and it spins at very high speed. When it starts to fail, the car feels flat, the engine can be noisy and the exhaust may smoke.

Many turbo failures are caused by something else, usually oil. So the real question is not only what has failed but why.

What are the symptoms of a failing turbo?

The commonest sign is a loss of power, especially when accelerating, with the car feeling sluggish as if the engine has lost its push. Next is noise: a high whine, whistle or siren that grows with revs, or a rattle or grinding from the engine bay. Smoke is the third, with blue-grey smoke suggesting oil is burning and black smoke suggesting too much fuel or too little air.

You might also see the engine management light or the car going into a reduced power mode, which some engines do to protect themselves.

• Noticeable loss of power or slow acceleration
• Whining, whistling or grinding that follows revs
• Blue-grey or black smoke from the exhaust
• Engine management warning light
• Rising oil use between services

What causes a turbo to fail?

Oil is the key. A turbo's bearings rely on a steady supply of clean oil, so old, dirty or low oil shortens its life. Blocked oil feed pipes, a worn engine that lets oil past, or switching the engine off immediately after a hard drive can all contribute.

Foreign objects entering the intake or exhaust can damage the blades. Leaks in hoses and pipes can also mimic turbo trouble without the turbo itself being at fault.

Is it the turbo or something else?

A split boost hose, a stuck actuator, a clogged particulate filter on some diesels, a faulty sensor or a leaking intake can all produce the same loss of power. For that reason a garage checks the cheap and simple things first, and reads fault codes before condemning the turbo.

It is worth saying that replacing a turbo without finding the cause is a false economy, because the new one may fail for the same reason.

Can I keep driving with a failing turbo?

Not if there is heavy smoke, a loud grinding or metallic noise, or a sudden dramatic loss of power. A turbo that breaks up can pass fragments into the engine, and oil can leak into the exhaust. Pull over safely and switch off.

If the problem is mild, such as a slight loss of power with no warning light, drive gently and arrange an inspection soon. Do not rev hard, and check your oil level when the engine is cold and the car is on level ground.

What does a garage do about turbo problems?

We inspect the pipes and hoses, check for play in the turbo shaft where accessible, look at the oil condition, read the fault codes and check for leaks. If the turbo needs replacing, the oil feed and return lines are normally checked and cleaned, and fresh oil and filter are fitted.

Cost depends on the engine, how hard the unit is to reach, whether the turbo is replaced or reconditioned and what else was damaged. Automaster is a garage at Longcombe Cross near Totnes, and we cannot promise a repair before an inspection, though you are welcome to ask for a quote.