4 Causes of Blue Smoke from the Exhaust
You’ve probably seen it before: While accelerating at a traffic light, the car in front of you emits a huge amount of blue smoke from its exhaust pipe. It’s not as extreme as a smoke bomb, but it’s not normal like someone else’s exhaust smoke.
Or maybe you’ve experienced blue smoke coming out of the engine bay every morning when you start your engine, regardless of the weather. Let’s take a look at what causes blue smoke from the exhaust and how much it can cost to fix.
What does blue smoke mean? Blue smoke means that oil is mixing with gasoline during the combustion cycle, and the oil is being burned and expelled through the exhaust along with the remaining partially burned fuel.
This means that your car is operating inefficiently, so you should investigate the cause as soon as possible. Generally, it means that oil is leaking because the gaskets are not sealing properly, so it will take some time. If the cause of blue smoke is a mix of oil and gasoline in the combustion chamber, the problem is more serious.
Why does my car have blue smoke?
1) Oil dripping into the manifold
As mentioned above, oil can leak from the seal between the engine block and head and drip onto the hot exhaust parts of the drivetrain. This creates blue smoke, which is pretty smelly. You may notice blue smoke coming from the rear of your car while accelerating or idling.
I recall a classic scenario when I looked at a 2002 Mitsubishi Montero and the owner mentioned she had the head gasket replaced, but after a quick test drive, she stated that she could smell oil burning from the very gasket, exactly as she said it had been repaired.
A defective cylinder head gasket often necessitates a cylinder head replacement. The only reason a head gasket needs to be replaced is because the head has gotten too hot and warped, allowing oil to leak through that gap.
2) Oil gets mixed into the fuel
Now, back to the blue smoke. Your car’s valve seals, piston rings, and PCV valves don’t last forever. And if you drive your car 10,000 miles between oil changes, the oil becomes less effective at reducing friction in your engine.
This means more heat is generated in the engine, causing the seals to heat up and cool, drying out and cracking.
If your piston rings are worn out, your engine will need to be replaced.
If this blue smoke only occurs after an oil change, you may have simply put in too much oil. This causes the oil to foam, reducing its lubrication and heat dissipation efficiency. Simply drain the excess oil and restart.
3) Oil Dripping onto Hot Engine Parts
Here’s another scenario: A cylinder head or valve cover gasket has failed and oil is leaking from the engine. The oil drips onto other hot parts of the engine bay (such as the headers) and evaporates into a cloud of blue smoke.
This smoke will come from under the hood when idling and out the back of the car when you drive. This is another reason why you should always pay attention to smells coming from your car.
Does it smell like something is burning? Have I smelled this before? Did someone leave a cheeseburger in the glove compartment? Ask yourself questions like these.
4) Bad Glow Plugs (Diesel Engines)
If you notice blue or black smoke when starting your diesel car or truck, you may have bad glow plugs. This means your car may not start as it should and may take longer to start than normal. Then connect a wire to each glow plug, one at a time, and see if you get a reading.
Should I drive with blue smoke coming from the exhaust?
This is because it’s not good for oil to mix with fuel and engines aren’t designed to do that. If the piston rings are worn and your car has high mileage, you’ll need to replace the engine. This will cost you between $2,500 and $7,000, which is money you don’t want to spend.
You don’t need to replace the engine, so have the problem looked at as soon as you see blue smoke. You may be able to drive your car for a few more years just by replacing the piston rings.
What If You Have Blue Smoke at Startup and Then It Goes Away?
Seeing some blue smoke emit from the exhaust pipe during initial cold engine startup is fairly common in older, high mileage vehicles. However, excessive levels of blue smoke that takes a long time to dissipate likely signals worn internal components.
This blue smoke specifically points to oil getting past aged cylinder pistons and rings and making its way into the combustion chambers.
At cold temperatures, the small gaps in between the pistons and chamber walls allow more oil to sneak past. But as the engine warms up and the components thermally expand, the gaps tighten up and the oil consumption/blue smoke gets reduced.
