Have you ever wondered what causes grey smoke from a diesel engine? Although this is a problem that is more likely to occur with older vehicles, it can also happen with newer cars as well. It might not necessarily mean something bad, but left unchecked it could lead to serious problems with the engine and the other systems beneath the hood.

What causes grey smoke from diesel exhaust when accelerating?

Grey smoke is a bit of a mystery. Is it bluish-tinted or is it very light black in colour? Because “grey” is a colour that can be interpreted differently, seeing a cloud of smoke coming out of your exhaust in that shade can mean a lot of things. However, truly grey smoke is most frequently caused by burning transmission fluid. 

Put simply, when it comes to grey smoke, diesel cars tend to emit it when they lack enough oil. But there are other reasons why you might start seeing grey coloured smoke. Besides from being a sign of excess oil burning in your diesel engine, the smoke could also indicate:

  • A faulty PCV (Positive Crankcase Ventilation) valve – This part is responsible for emission control. It reduces the car’s emission as it draws unburnt fuel back from the lower part of the engine back to the top. Over time it wears out and causes the grey-coloured smoke. Repairing it is an easy and straightforward job.
  • Leak in the transmission system – If your car has an automatic gearbox then you should definitely inspect for leaks. If fluids are drawn into the engine through a leak it can cause costly repairs.
  • Jammed turbocharger – Burning excessive amounts of oil, slow acceleration and excessive grey coloured smoke are the typical signs of a worn-out turbo. The longer your drive your vehicle with a failing turbo, the more damage you cause to your engine and therefore the most costly it will be to fix.

If you are unsure what causes grey smoke from a diesel engine, make sure you visit your local mechanic for assistance. If problems are left unattended, the more damage can be caused to the car’s most important component – the engine.

Keep seeing grey exhaust smoke after an oil change?

It is not normal to keep seeing grey smoke from diesel engine after you checked the oil filter and changed the fluids. If that is the case, then you might experience any of the following: an oil leak such as worn cylinder walls, damaged piston rings, or leaking valve seals. If you have done everything from your car’s owner manual booklet and are still getting grey smoke from your diesel exhaust pipe when accelerating, then you should definitely inform your mechanic next time you visit the local garage.

How to prevent grey smoke in diesel cars?

Before you rush bringing your vehicle in for service, here is something you should know. Besides jumping straight into the engine rebuild project, many drivers decide to narrow the cause down by starting at the lowest cost and working upwards. This is why what you should do first is opt for an oil change. There are special oil treatment products on the market that can help remove the built-up coked and varnished oil and soot, help the seals and rings do their job, and prevent future coking, which in turn restores compression. Cleaning of the turbo is another thing that will make your engine run more efficiently and smoother. Another solution for the backyard mechanic is the replacement worn-out parts such as the PCV valves. 

So, let us wrap things and make it easier for you. If you are wondering why you see grey smoke from diesel engine, you should inspect the following:

  • the oil filters;
  • the piston rings; 
  • the valve seals;
  • the PCV valves;
  • the turbo seals;
  • the turbo itself;
  • and transmission.

What to do when you see grey smoke coming from your exhaust pipe?

Smoke can mean a lot of things but this should not necessarily make you think the worst. In most cases, the repairs will involve just the replacement of a seal or an oil filter rather than a complete engine rebuild. If you are unsure of your car repair skills, it is highly recommended that you visit the mechanics at The Motor Company in Leicester for a complete vehicle’s diagnosis. It gives your peace of mind and oftentimes, it is not as expensive as a DIY project.