What Happens When the Turbo Goes on a Diesel? Understanding Turbo Failures in Diesel Engines

When a turbo goes on a diesel car, the first thing most drivers notice is a loss of power, often with smoke from the exhaust and a whining noise. Many diesels then drop into limp mode to protect the engine. In the worst cases, oil from the failed turbo can feed the engine and cause diesel runaway, which is why a failing turbo on a diesel should never be ignored.

This guide covers the warning signs, what happens if the turbo fails while you are driving and how to reduce the risk of it happening.

Signs of Turbo Failure in Diesel Engines

Diesel turbos tend to give plenty of warning before they fail. These are the signs to look out for.

Decreased Engine Performance

The car feels sluggish and less responsive, especially when pulling away, towing or climbing hills. Diesels rely heavily on the turbo for their pulling power, so a drop in boost is usually easy to feel. It can happen gradually or all at once.

Excessive Exhaust Smoke

Blue smoke means oil is being burned, often because oil is getting past worn turbo seals into the intake or exhaust. Black smoke means the engine is burning more fuel than it has air for, which happens when the turbo is not delivering enough boost. Our guide on blue smoke from the turbo goes into more detail.

Unusual Whining or Whistling Noises

A failing turbo may produce a whining, whistling or siren-like sound that gets louder with engine revs. This is often down to worn bearings. It is a warning that parts inside the turbo may soon start to make contact.

Increased Oil Consumption

If oil escapes into the exhaust or intake, it gets burned off and the oil level drops faster than normal. Regular topping up between services, with no visible leaks, is a common sign of a failing diesel turbo.

Limp Mode

Most modern diesels will cut power and limit the revs when they detect a serious boost fault. You may see an engine warning light and a code such as P0299 for underboost. Limp mode protects the engine, but it does not fix the fault.

For a full list of warning signs on any vehicle, see our guide to the signs of a failing turbo.

What Happens If a Turbo Fails While Driving?

If the turbo fails suddenly, you will usually feel a sharp loss of power. There may be a loud whine or bang, a cloud of smoke from the exhaust and a warning light on the dashboard. The car may drop into limp mode straight away.

The safest thing to do is pull over when it is safe, switch the engine off and check for oil or smoke under the bonnet. Avoid restarting the engine again and again to see if the fault has cleared. If the turbo has lost oil, running the engine can cause further damage. Our guide on whether you can drive with a blown turbo explains the risks of carrying on.

Diesel Runaway

Diesel runaway is a rare but serious risk that is specific to diesel engines. A diesel does not need a spark to ignite its fuel. If a turbo fails and its seals let engine oil into the intake, the engine can start burning its own oil as fuel. The revs then climb on their own and turning the key off will not stop it, because the engine is no longer relying on the fuel system.

Signs of runaway include revs rising without your foot on the accelerator, heavy smoke and a loud, rising engine note. The usual advice on a manual car is to select the highest gear, hold the car firmly on the brakes and release the clutch to stall the engine. Once stopped, do not try to restart it. If it cannot be stopped, get yourself and any passengers well away from the vehicle.

Consequences of Turbo Failure in Diesel Engines

Turbo failure can affect far more than the turbo itself.

Engine Damage

If the turbine or compressor blades break, fragments can enter the engine. Oil starvation, overboost and runaway can also cause serious internal damage. Our guide on whether a turbo can damage your engine explains how.

DPF and EGR Problems

Oil and extra soot from a failing turbo can clog the diesel particulate filter and the EGR system. This leads to more regenerations, warning lights and, in time, expensive repairs. The link works both ways, as our guide on whether a blocked DPF can cause turbo failure explains.

Higher Fuel Use and Emissions

Without enough boost, the engine burns fuel less completely. Fuel economy drops and the engine produces more soot and harmful emissions, which can also cause problems at the MOT.

Stalling and Reduced Reliability

A failing turbo can cause rough idling, stalling or difficulty holding power under load. For businesses running vans, this means unexpected downtime as well as the repair bill.

Preventive Measures to Avoid Turbo Failure in Diesel Engines

Most diesel turbo failures come back to oil. Regular servicing with the correct grade of oil, and changing the oil and filters on time, gives the turbo the clean lubrication it needs.

Give the engine a moment to warm up before working it hard, and let it idle briefly after a long or heavy run so the turbo can cool. Our guide on how to warm up and cool down your turbo explains why this helps.

Finally, act early. Power loss, smoke or new noises are much cheaper to deal with before the turbo fails completely. Our guide on how to make your turbo last longer has more tips.

Get In Touch

If you think your diesel turbo is failing, we are here to help. At Essex Turbos, we supply reconditioned turbos, remanufactured and new units with a one to two year unlimited mileage warranty. We have a huge range of stock, from Mercedes-Benz to Range Rover, Audi to Jaguar, and Renault to Ford. Simply get in touch today and we will have your turbo shipped in no time.