Blue Smoke from Your Exhaust: What It Means & How to Fix It

One of the last colours you might expect your exhaust smoke to be is blue. As you’ve probably guessed, it’s a sign that something is wrong and shouldn’t be ignored. While spotting blue or grey smoke can be alarming (and confusing), there’s a simple explanation: your engine is burning oil. 

Here, we discuss the possible causes of blue exhaust smoke and what you should do about it. If blue doesn’t quite describe the colour of the smoke, we also have guides covering black smoke and why your car might be overheating.

Looking for white smoke? See our white smoke guide here.

Looking for black smoke? see our black smoke guide here.

What makes exhaust smoke blue?

Bluish or grey exhaust smoke signals that oil is seeping into the combustion chamber, where it is burnt along with air and fuel. There is probably a worn or faulty engine component that has started to leak. In older vehicles, leaks are often caused by the natural deterioration of parts; in newer cars, a defective component is the more likely explanation.

Why is there blue smoke from my exhaust when accelerating?

The most likely explanation for blue smoke that specifically appears when you accelerate is damaged piston rings. They rely on seals to prevent oil leaks, but these can become worn and cracked over time. Read on to find out more about this problem.

Eight causes of blue exhaust smoke

Below is a comprehensive list of all the reasons why your exhaust smoke might be blue.

1. Worn engine oil seals

Engine oil has to make its way around the engine, lubricating the correct components without entering places it shouldn’t be, like the combustion chamber. It is kept out of these places by seals that may become worn over time, allowing oil to leak through them.

Malfunctioning seals should be replaced immediately, but locating them isn’t always easy - it’s a job best left to professional mechanics.

2. Blown head gasket

When head gaskets fail, they are notorious for leaking oil, which can make its way into the exhaust system and other places it shouldn’t be, where it makes contact with hot surfaces and produces blue smoke.

Other head gasket failure symptoms

• Coolant loss without any leaks from the cooling system

• White, milky-looking discolouration of the engine oil

• Overheating engine

• Loss of power

• Sweet smell from the exhaust

When your head gasket blows, you should stop driving immediately, or you could cause more damage to the engine. The following guides contain helpful information:

• What Happens When Your Head Gasket Is Replaced?

• Guide to head gasket sealants

Repairs are unfortunately expensive, costing £798.27 on average when booked through FixMyCar, though they can be £1000 or more depending on the make and model of your car.

3. Worn pistons and piston rings

Pistons convert the energy from combustion into a mechanical action, transferring it to the crankshaft. They depend on piston rings, which create an air-tight seal in the cylinders of the engine. When either the pistons or rings become worn, oil may start leaking into the fuel, creating blue smoke when the mixture is burnt. 

Replacing pistons is a challenging job that you shouldn’t undertake without the required expertise. 

4. Leaking inlet manifold

The inlet manifold distributes air to the engine cylinders, ensuring enough is available when the valve opens during every intake stroke. If it starts to leak and allows oil in the cylinders, the oil will be burnt along with the fuel - by now, you know the result.

You can purchase inlet manifold sealants, providing a temporary fix for small leaks. However, sealant is not a long-term solution and is unsuitable for a significant leak.

5. Damaged valve stem seals

Valves control the amount of fuel and air allowed into the cylinders. They are fitted with high-strength rubber seals, which are pretty durable, but they can still become cracked due to high temperatures and general wear.

If faulty valve stem seals are the problem, a mechanic will often use specialised tools to compress the valve spring before making a replacement.

6. Blown turbocharger

This explanation applies specifically to cars fitted with a turbocharger. When this component blows, you will likely notice a large cloud of blue smoke from the exhaust caused by a broken oil seal or damaged turbo casing inside the turbocharger, allowing oil to seep into the intake manifold.

The average quote for a turbo replacement on FixMyCar is £747.06.

7. Faulty PCV valve

PCV stands for positive crankcase ventilation. This type of valve is crucial in removing exhaust gas and unburnt fuel from the engine block. Engine valves are notorious for getting stuck, especially as they age, and when this happens, it allows air, oil and other gases to mix within the engine, producing blue smoke.

Fortunately, PCV valves are affordable to replace.

8. Defective glow plug

This fault applies to diesel cars only; petrol engines have spark plugs. Read this guide for more information about the difference between spark and glow plugs.

A bad glow plug is probably to blame if you notice blue-white smoke from your exhaust when you start the car, which disappears after the engine has heated up.

Other signs of defective glow plugs

• Slow starting

• Failure to start

• Engine misfires

• Decreased fuel efficiency

Find out more about what happens when your glow plugs fail.

Glow plugs should be changed roughly every 100,000 miles or sooner if they develop a fault. The average quote for replacing glow plugs is £230.96.

How do you fix blue smoke from your exhaust?

Since there are so many possible explanations for blue smoke, you may not be able to narrow down the exact cause of the problem yourself, so it’s best to consult a reputable mechanic who will recommend the proper repair.

Fixes for blue smoke include:

• Try running a stop leak additive through the system

• Replace engine oil seals

• Replace blown head gasket

• Replace piston rings

• Use inlet manifold sealant or replace the part

• Replace valve stem seals

• Repair turbocharger

• Replace glow plugs

Will thicker oil stop blue smoke?

Blue smoke isn’t usually a sign that you need to change the type of oil you’re using - it’s a sign your car has an oil leak somewhere in the engine. The only solution is to locate and repair the source of the leak.

Can I drive my car with blue smoke?

You should avoid driving your car when you notice blue smoke from the exhaust and take it to a garage as soon as possible to be repaired. If you keep going, it will likely cause more damage, or your vehicle may die completely - which you don’t want to happen when you’re travelling down a busy road.

Rather than taking your car to a garage, you could find a mobile mechanic to perform diagnostic tests where you are. However, if the repair is extensive, it may have to be done in a specialised environment.

If you found this article helpful, you might also like:

• Why is black smoke coming from my exhaust?

• Why is white smoke coming from my exhaust?

• Why is my car overheating?

• Diagnose car problems & find the right fix

• Why does my car make a hissing noise?

• The ultimate guide to exhausts

• How much does it cost to repair an exhaust?

• Why do MOT tests include an exhaust emission test?

• Can you drive with a broken exhaust?

• Why is my car misfiring?

• Why can I smell petrol in my car?

• Why does my car lose power?

• Why is my car burning oil?