Updated at: 17-07-2022 - By: Lucas

Regardless of the color of the smoke coming from the exhaust, if the engine is cold, there is a good chance that there is an issue that has to be addressed.

Smoke is frequently caused by worn valve seals, blocked piston rings, incorrect oil viscosity, or low-quality engine oil, among other things. Bad glow plugs and difficulties with the high-pressure pump can cause smoke from diesel engines’ exhausts. Using low-quality diesel fuel can exacerbate these issues.

Why does smoke come out from the exhaust?

Engine Smokes On Startup-2

You need to know the color of the smoke, which can be white, gray, or dark blue, in order to figure out what is causing this issue.

Worn valve seals

In order to protect the cylinders from being lubricated, the valve seals are responsible for preventing oil from leaking into the combustion chamber.

This means that a tiny quantity of oil gets into the cylinders when the engine is cold because the spaces are smaller, and when the engine heats up, those same gaps widen, and no more oil gets into the cylinders. When you first turn on your computer, you may notice a puff of blue smoke, which fades away after a few minutes.

Some engines’ design allows for a little quantity of oil to enter the cylinders while the machine is idle, which can lead to worn seals in the valves. Because this oil is consumed quickly upon starting, cars no longer emit smoke after a short period of time.

Piston rings overlap

Overlapped piston rings are also a common cause of smoke on engine start-up. As a result, the exhaust will typically emit a cloud of gray and white smoke.

Because of damaged piston rings, oil can enter into the cylinders. When the engine is cold, this is a common occurrence, so be aware of it. This can be dangerous, so you’ll need to remove soot and carbon deposits from the engine to get it back in working order when the vehicle has warmed up.

This problem can be solved by removing the engine and inspecting the piston rings. However, it’s best to check the engine’s compression before proceeding. Additives can also be used as a short-term treatment, although this is only a temporary fix.

Using an incorrect oil for your engine

I’m referring to a vehicle with a high-mileage engine. Car owners manuals frequently state that varied viscosities are acceptable for use in the engine. The likelihood of this happening decreases dramatically as the engine ages and wears out.

It will leak into the cylinders when using thinner oil until the engine warms up and the clearances widen, which is why thicker oil is recommended. With a heavier oil, this is much less likely to happen.

Pay attention to the quality of the oil as well. Even if you picked the viscosity right, exhaust smoke may still be present, but the oil’s poor quality may put you in danger.

In a few rare instances, drivers noticed that the exhaust smoke stopped appearing after changing the oil filter, indicating that the oil filter was either phony or defective for the model of automobile in question.

Worn or damaged cylinder head gasket

Engine Smokes On Startup-3

Cylinder head gasket failure is the most common cause of coolant leakage into the cylinders. White smoke from the exhaust is a sign that coolant is in the cylinders when you start the car.

It’s also possible that the cylinder head isn’t tight enough, which would explain why the white smoke disappears after warming up and the metal expands again, restoring the tight fit.

Failing engine sensors

Fuel mixture composition is controlled by the electronic Control Unit (ECU). Coolant and intake air temperature sensors are among the sensors that play a role here.

Consequently, the ECU may employ a fuel mixture that is overly enriched on beginning, resulting in black smoke from the exhaust. Upon reaching operating temperature, the fuel mixture gets leaner as the engine cools and returns to its original state.

Condensation in the exhaust

The engine doesn’t have a problem with condensation. During the colder months of the year. Condensation accumulates on the exhaust system’s walls after the engine has cooled down. When the engine is started in the morning, the exhaust fumes warm up this condensation and cause it to condense, resulting in steam.

So it takes a few minutes for the exhaust steam to evaporate after beginning. Temperature, engine size, and exhaust system design all affect evaporation time. Because of this, there’s no need to be concerned if you see this.

Smoke from the exhaust on startup in diesel engines

When you start a diesel engine, you’re more likely to observe smoke coming out of the tailpipe, especially if the engine is cold.

Faulty light bulbs. You’ll notice black smoke from the exhaust if the glow plugs in your diesel engine aren’t working properly because the fuel isn’t burned entirely in the cylinders. However, this is only going to last for a short while as the black smoke will go away as the engine warms up.

The injectors are faulty. To put it another way, partial fuel combustion can be caused by a faulty injector nozzle or a lack of pressure when spraying fuel from the injector.

In a similar fashion to the previous cause, black smoke can be seen coming from the exhaust when the engine is cold and it will dissipate after the engine warms up.

A faulty PCV valve is to blame (crankcase ventilation system). Oil is burned in conjunction with fuel when a PCV valve engine fails. Black or dark blue smoke can be seen until the engine heats up.

How to diagnose and stop smoke from the exhaust

There are several things to examine if you notice smoke coming from the exhaust, and the following is a list of them:

  • Check the valve seals. This is a common cause of why smoke comes out from the exhaust on startup, especially if the engine is cold. When you begin to perform these checks, you can start with the valve seals. Again using a high-quality engine oil will prolong the life of the valve seals.
  • Check your oil level and condition in the engine. If you see an increase in the oil’s volume, then most likely coolant got into it. So if you see noticeable changes in their levels, you’ll need to perform additional checks in a car workshop to see if valve seals, piston rings, or the cylinder head gasket have problems.
  • Check the oil quality and viscosity. Low-quality oil and its wrong viscosity are bad for the engine, especially if the engine has high mileage. If you used an incorrect oil viscosity for your engine, then it makes sense to replace it with a thicker one if the engine is more worn out, or with the proper viscosity by checking your car user manual.
  • Check the engine compression and the piston rings. If you see black or gray smoke on engine startup especially if the engine is cold, this is a good reason to check the compression and the condition of the piston rings. If the compression is low, you need to find out the causes. Cleaning the piston and rings from carbon buildups often solves the problem. If you notice a consistently high-oil consumption then it makes sense to change the piston rings.
  • Check the engine sensors with a scan tool to see if you have a failing one

Additional checks for diesel engines

  • Check the condition of the injectors. Bad diesel injectors are a common cause why you will see black smoke from the exhaust. So it’s better to check them out.
  • Check the high-pressure pump.
  • Check the EGR. Another common cause is why diesel engines have smoke on startup. Cleaning often is a solution, but if the EGR does not function properly after that, change it.