Will Oil on Spark Plugs Cause Car Not to Start?

Written by

Charles Bolte


Vernon Hoppe 

will oil on spark plugs cause car not to start

Most car owners have experienced their car failing to start in one way or another. There can be many reasons why your vehicle refuses to run, and you might find yourself asking: Why are my spark plugs wet with oil? Will oil on spark plugs cause car not to start?

Spark plugs are an essential part of your car’s ignition system. They ignite the air-fuel mixture in the engine and begin the combustion process. Any interference with their performance can stop the combustion process.

Getting oil or dirt in your spark plugs can prevent or delay them from sparking, mess with the delicate nature of car ignition, and may cause your vehicle not to start.

So why won’t your car start with spark plugs with oil on them? And what are the oil on spark plugs symptoms? Read below to find out.

Causes of Oil on Spark Plugs


Finding oil in your spark plugs is usually a symptom of a much larger issue in your car. The problem is typically in your ignition or lubrication system. Here are some problems that can cause oil to get on spark plugs.

1. Worn or damaged valve cover gasket


The valve cover gasket is responsible for sealing the engine’s valve cover to prevent oil leaks in your engine. However, the gasket can deteriorate and become brittle. When this happens, you may have oil in spark plug well.

2. Faulty O-rings


Spark plug tube seals or more commonly known as “O-rings” are designed to prevent oil from entering your spark plug wells. These seals can be damaged or wear out after long use, causing oil to come out.

3. Faulty piston compression ringsFaulty-piston-cause-oil-to-get-on-spark-plugss

Compression rings keep oil out of your car’s combustion chamber and the cylinder walls. Worn-out or faulty piston compression rings have a hard time stopping any oil from leaking into your spark plugs.

4. Piston wear or cylinder wall damage


Worn pistons or damage to the cylinder walls can allow oil to bypass the piston rings and enter the combustion chamber. From there, the oil can be expelled through the exhaust or find its way into the spark plug wells.

A faulty piston and piston ring can affect the engine, causing misfire and unusual noises.

5. Blown head gasket


Head gaskets seal off the combustion chamber to prevent engine oil and your car’s coolant from mixing together. Due to overheating, your head gasket can perforate, which can cause leaks that will drench your spark plugs in oil.

6. Damaged valse seal or valve guide


Both of these components regulate airflow in the combustion chamber. Damage to either of them due to normal wear and tear or improper installation can cause oil to gather on spark plugs.

7. Clogged crankcase ventilation valve


These ventilation valves often last for ten years before they need replacing. Other than that, blockage in them can increase pressure inside the crankcase, causing oil to come out of the spark plugs to relieve the buildup.

Effects and Symptoms of Oil on Spark Plugs


When engine oil comes into contact with your car’s spark plugs, it can have several adverse effects on your car’s performance and operation. Let’s take a good look at some of the most common effects of oil in spark plugs.

  • Blue Smoke Coming from the Exhaust

A cloud of blue or white smoke coming from the exhaust is a sign of too much fuel in your combustion chambers. When your combustion system isn’t working efficiently, your car would need to pump more gas so that the engine can run properly. This leads to some fuel getting pumped out into your exhaust system.

  • Engine Misfire

An engine misfire often manifests as a shaking motion from your vehicle when you try to accelerate.

Misfires cause rough idle, leading to increased fuel consumption and strong emissions that can further affect fuel efficiency.

  • Engine Backfire

Engine backfires happen when fuel combusts outside of the combustion chamber. This causes a small explosion in the exhaust and can damage or destroy it in the process. A broken exhaust can lead to further problems, such as toxic fumes entering your cabin and increased repair bills.

  • Low Fuel Efficiency

Spark plugs work at very high temperatures, sometimes at 500℃ for newer models. Imagine exposing oil to spark plugs at that level of heat! Oxidation will form, and the plug’s efficiency will decline as it needs more fuel to burn.

If you think you have oil on spark plugs but no smoke comes out of the exhaust, checking fuel consumption and mileage is a great way to narrow down the problem.

  • Poor Engine Performance and Dead Starts

Spark plugs contaminated with oil can cause poor engine performance, since the gas mixture in your combustion chamber isn’t burning efficiently. Your car’s pistons will not have the necessary pressure needed to work. This causes your car to accelerate slowly, since it needs to compensate for the slow combustion.

A dead start may also occur, in which the engine seems to crank then completely stops working.

Diagnosing and Fixing the Issue

It is important for your car’s health to avoid harm from an oil leak getting into your spark plug. It is essential to find the main cause of the contamination and fix it immediately. Here are some steps on how to diagnose and fix oil on spark plugs.

1. Conduct a visual inspection


Turn off your engine and disconnect the battery from the terminal. Visually examine the cylinder heads from the outside and remove your car’s valve cover. Remove the spark plugs and inspect their condition. Look for any signs of oil contamination like oil deposits in the electrodes.

2. Clean head and valve covers


Cleaning the head and valve covers is the next step when replacing a broken valve cover gasket. Before installation, you must ensure that the head and valve covers are free from any contaminants and particles. This will allow the new parts to create a better seal.

3. Install new valve cover and spark plug gasket


Add a liquid seal around the edges of the gasket so that it does not slip. This step creates a good bond to stop oil from getting into the spark plug. Finally, install the spark plug gasket on the spark plug well. Make sure to bolt the nuts tightly.

4. Perform engine compression tests


Installing new gaskets is mostly the answer for most oil leaks in spark plugs. If the above method does not work, engine tests need to be conducted to find out why oil leak cause a car not to start.

An engine compression test involves attaching a gauge to your spark plug hole, disabling the ignition and fuel system, removing the spark plugs, and cranking the engine.

The readings will determine if your cylinders are producing the required good compression for your car. If there is a 10% difference between the cylinders, there is most likely oil in their spark plugs.

5. Professional diagnosis


Diagnosing oil in spark plugs can be a difficult process, and multiple factors can contribute to the problem. Getting a professional examination from a qualified mechanic can allow you to accurately determine the leak and provide appropriate recommendations for repairs.

However, in case you don’t have time for the solutions above, you can temporarily remove the spark plugs with a torque wrench and a socket to clean them.

Use some towels to wipe away the oil leak and turn the engine over to clean the spark plug wells.

Preventing Oil Contamination on Spark Plugs


Here are some things you can do to prevent oil from getting on your spark plugs:

  • Regular maintenance like scheduled oil changes and using the correct type of oil
  • Do regular inspections on the head gaskets, spark plugs, and piston rings
  • If you notice any symptoms of oil in your spark plugs, get your car checked immediately.

Frequently Asked Questions


Is it safe to drive with oil on spark plugs?

A car with oil on its spark plugs is still drivable. However, your car may experience misfires and backfires, which can lead to accidents. It is not recommended that you drive with contaminated spark plugs.

How often should spark plugs be inspected and replaced?

Car won’t start spark plugs changes are not two things you want to worry about at the same time. The intervals with which you should replace spark plugs are dependent on the type your car uses. 30,000-50,000 miles are typical for nickel and copper spark plugs, while 60,000-150,000 are common for platinum and iridium spark plugs.

Should I seek professional help for oil on spark plugs?

Finding your spark plugs with motorcycle oil is a serious issue. If not repaired quickly and properly, this can lead to further issues down the line that will cost you more for repairs. Seek professional help if possible.


So will oil on spark plugs cause car not to start? Yes. When you find oil in your spark plugs, it is important to address the issue immediately. Contamination can lead to poor ignition, misfires, and decreased fuel efficiency.

To ensure that your car is reliably starting and performance is optimal, regular maintenance is essential. Inspecting spark plugs and checking forl indications of oil contamination early as well as regular oil changes can prevent further problems.

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