To keep your exhaust in good condition, you need to be able to spot when something is wrong.

Any unusual exhaust noises, smoke or leaks can all signal that your vehicle has an exhaust problem.

Read on and find out if you have an exhaust problem, why your exhaust may be smoking and why it may be making noise.


Signs You Have an Exhaust Problem

Your vehicle could be experiencing an exhaust problem if you notice any of the following warning signs:

A mechanic will be able to advise you as to whether you require an exhaust repair or replacement. 


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Why is My Car's Exhaust Smoking?

Your car exhaust could be smoking for several reasons, including:

  • A leaking head gasket
  • A faulty coolant system
  • Burnt electrical wires
  • Worn out pistons
  • Faulty fuel valves

If you regularly maintain and service your vehicle, then any visible exhaust emissions will likely not be an issue – though you should still check this.

When diagnosing a smokey car exhaust, take note of when and where the smoke appears.

If the smoke only appears when the car is stationary, there could be a different issue to smoke that appears when accelerating, for example.


Fire Under the Bonnet

If you identify that the smoke is being caused by a fire under your car bonnet, you need to turn off the engine immediately.

Pull the bonnet release lever – do not attempt to prop it open.

Everyone should exit the vehicle and stand well back.

You should call the emergency services.


Car Smoking but Not Overheating

If your car is smoking but not overheating, then this could be the result of any of the following issues:


White Smoke

If you notice white smoke coming from your exhaust, this is likely steam caused by condensation in the exhaust pipe.

Alternatively, your vehicle could be leaking coolant or experiencing head gasket failure.

White smoke coming from your car exhaust can be caused by a cracked engine block or damaged coolant or radiator hoses.


Black Smoke

If you drive a petrol car and see black smoke, then it is likely that too much fuel is being burned off.

Your vehicle may also be suffering from air filter or fuel injector problems.

If your drive a diesel car, then a blocked diesel particulate filter (DPF) could be to blame.

Provided the filter has not become excessively blocked, you should take your car for a long drive on the motorway to try and trigger the regeneration process so that the filter can clean itself.


Blue Smoke

Dark grey or blue exhaust smoke signals that your engine is burning oil.

This can leak into the combustion chamber where it is burned with fuel.

Your engine may misfire when you turn the keys in the ignition or the vehicle may shake more when idle if this is the case.

These leaks can be caused by any of the following components being worn out or damaged:

  • Head gasket
  • Inlet manifold
  • Engine oil seals
  • PCV seals
  • Valve stem seals
  • Pistons
  • Piston rings

You should have your vehicle inspected by a professional mechanic if you notice blue exhaust smoke.


Grey Smoke

Thick grey exhaust smoke usually means that your vehicle is burning oil.

When this leaks into the combustion chamber, this can reduce fuel economy and cause damage to the catalytic converter.

A faulty valve stem seal or piston ring could be to blame.

Blueish grey exhaust smoke when accelerating will need to be addressed by a professional mechanic, as the piston rings could be damaged. 


Why is My Exhaust Noisy?

Different sounds can point towards different exhaust issues.


Hissing Noises

Hissing sounds are often a sign of an exhaust leak, signalling there could be a crack in the exhaust pipe, exhaust manifold or a leaking gasket.


Roaring Noises

A roaring noise can indicate that there is a car sound silencer problem.


Chugging Noises

There could be a blockage in the exhaust system if you hear a chugging noise.


Rattling Noises

An exhaust rattle usually indicates that the system has come loose or suffered a misalignment.


Where is the Noise Coming From?

In addition to determining the type of noise you’re hearing, working out where the sound is coming from can help you pinpoint why your exhaust is noisy.


Front of Car

If you notice loud exhaust sounds coming from the front of your car, then you may have a bad gasket, a loose flexible pipe connection or a cracked exhaust manifold.


Centre of Car

If your hear exhaust noises from under the centre of the car, then there could be a loose connection or a hole in your exhaust.

Alternatively, there could be a problem with the catalytic converter – which will likely be expensive to repair.


Rear of Car

Noises from the rear of the vehicle are usually related to the muffler or caused by a hole in an exhaust system pipe.


What is a Car Exhaust?

Your car’s exhaust system manages the expulsion of gases produced during the engine combustion process.


What Does a Car Exhaust Do?

The exhaust in a car serves 4 main purposes:

  • Noise control
  • Improving engine performance
  • Improving fuel consumption
  • Directing exhaust fumes away from passengers

All exhausts produce gases as emissions, and the exhaust emissions system channels these noxious fumes away.

Exhaust gases are collected from the cylinder head in the engine by the exhaust manifold, which diverts the gases from the engine cylinders and releases them through the front pipe.

The exhaust gases go through the catalytic converter, which removes the harmful elements and converts them into inert gases.

These gases can then pass through a silencer or a muffler before exiting via the tailpipe.


How Much is a New Exhaust?

Whilst this will vary depending on your vehicle and where you’re based in the UK, an exhaust replacement can cost as much as £2,000.

An exhaust repair can cost up to £600.

Parts and labour costs will also have an impact on the price.

If you notice that your engine is becoming noisier, the exhaust is corroded or you are having to fill up more often, then you may need a new exhaust. 


Why Do MOT Tests Include an Exhaust Emissions Test?

The emissions test is part of MOT testing to ensure vehicles in the UK comply with government standards.

The exhaust emissions test ensures that the pollutants emitted from your vehicle’s exhaust are within the legal limits.

This test is mandatory for all diesel, petrol and gas-powered vehicles that have 4 or more wheels.

Depending on when your vehicle was first used, the test may be visual or it may be a metered smoke test.

If your vehicle produces higher emissions than expected, you could fail the MOT test.

Please note that your vehicle could be tested during a roadside check.

To give your vehicle the best chance of passing, you should book regular car services and deal with exhaust problems quickly.


How to Prevent Exhaust System Problems

To reduce the likelihood of exhaust system issues occurring, you should have your exhaust system inspected every year.


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Regular car servicing and vehicle maintenance can help to prevent exhaust system damage.