Will Oil on Spark Plugs Cause Cars Not to Start?

You’re running late for work, rushing to your car and turning the ignition, but it’s not starting. As you pop the hood open, notice oil on your spark plugs. Could it be the culprit behind this frustrating scenario? More specifically, will oil on spark plugs cause cars not to start? 

The short answer is “partly yes”. When oil seeps into the spark plug chamber, it coats the electrodes and interferes with spark formation. This lack of proper ignition can prevent the engine from starting. Even if the engine does manage to start, you’ll notice misfiring or rough idling 

Before you slam the steering wheel in exasperation or start searching for towing services, give us a moment to provide you with a precise guide on this matter. You’ll find everything in detail here, from the symptoms to common causes and solutions. 

Related: Are Car Spark Plugs Universal? The Truth About Car Spark Plugs

Will Oil on Spark Plugs Cause Cars Not to Start?

As we answered shortly, oil on spark plugs can cause a car not to start. Now, let’s dig into the whole fact in detail. Basically, it can happen in different ways depending on whether there is fresh or burned oil. 

Fresh oil acts as an insulator, preventing the spark plug from generating enough electricity to ignite the fuel mixture in the combustion chamber. Excessive oil on the spark plugs may result from various underlying problems, such as worn piston rings or valve seals that allow oil to leak into the combustion chamber.

Oil seeps into the cylinder when these components fail, coating the spark plugs with a thin film. Consequently, the spark produced by the plug becomes weak or non-existent, making it difficult for the engine to start. 

On the other hand, burned oil has carbon-rich residues that possess conductive properties. Suppose this carbon residue finds its way into the spark plug boot. In that case, it can cause misfires by establishing an alternative route for electrical current to travel directly from the plug wire to the cylinder head, bypassing the spark plug.

Impact of Oil On Spark Plugs

Sadly, the impact of oil on spark plugs is not limited to starting difficulty. If you explore more deeply, you can see there are many negative consequences of this. However, you don’t need to take the hassle; we have explored and discussed those consequences below. 

Potential Engine Issues Caused By Oil on Spark Plugs

Oil on spark plugs can cause various engine issues, leading to poor performance and decreased fuel efficiency. One potential problem is misfiring, which occurs when the spark plug cannot ignite the air-fuel mixture properly. 

As a result, the engine may experience rough idling, hesitation, or even stalling. Furthermore, oil contamination on the spark plugs can also lead to decreased power output and acceleration.

Another issue related to oil on spark plugs is fouling. In this situation, excess oil causes carbon deposits to accumulate on the electrode and insulator of the spark plug. These deposits interfere with the electrical current flow and hinder optimal combustion. Consequently, drivers may notice reduced engine power, higher fuel consumption, and difficulty starting their vehicles.

Damage to the Spark Plug 

Prolonged exposure to oil can cause corrosion on the metal components of the spark plug. This corrosion weakens or damages crucial parts like the shell or threads, leading to potential leaks or loose connections. 

Moreover, excessive oil contact can degrade the insulation properties of the spark plug’s boot or wire connector system, potentially resulting in arcing or electrical shorts.

Risk of Failure of Other Related Components

when oil coats the spark plugs’ electrodes, it creates a barrier that prevents proper sparking. Consequently, unburned fuel may pass into the exhaust system and cause damage to components such as the catalytic converter. 

In addition, prolonged exposure to contaminated spark plugs can lead to carbon deposits accumulating on them. Carbon buildup can further hinder ignition and lead to increased emissions. 

Common Causes of Oil on Spark Plugs

We have seen people frequently asking, “Why are my spark plugs wet with oil? This is quite usual as the spark plug sits in such a position surrounding different components with oil or lubricant. However, we have found a few common causes responsible for this issue. Let’s take a look at them. 

Worn Piston rings or valve seals

Worn piston rings or valve seals are common culprits for oil on spark plugs. These components are crucial in maintaining proper engine compression and preventing oil from leaking into the combustion chamber. 

When the piston rings wear out or become damaged, they can no longer create a tight seal between the piston and cylinder wall, allowing oil to flow past and onto the spark plug. Similarly, worn or faulty valve seals can allow oil to leak down into the intake or exhaust valves, resulting in oil contamination on the spark plug.

Worn or Damaged Valve Cover Gaskets

Depending on the engine configuration (OHV SOHC DOHC), they may also include intake and exhaust valves, valve springs, cam(s), valve guides, and other components. These components require lubrication, which is why engine oil is poured from the oil pan to the heads. 

The valve cover gaskets are crucial in keeping oil on the cylinder heads and preventing it from spreading to other engine parts. However, these gaskets wear out over time due to the high temperatures involved, allowing oil to escape. This can lead to oil reaching the spark plugs in Over Head Valve (OHV) designs. 

Engine overfilling with oil

Engine overfilling with oil is another common cause of finding oil on spark plugs. While it may seem counterintuitive that having too much oil can lead to this issue, the excess oil can seep into the combustion chamber and coat the spark plugs. 

One possible reason for engine overfilling with oil is inaccurate or faulty measuring tools. If you rely solely on the dipstick to check your oil level, ensuring its accuracy is essential. Another factor contributing to engine overfilling is improper pouring technique during DIY oil changes.

Degraded Spark Plug O-ring

The spark plug O-ring, found on the valve cover of both Single Over Head Cam (SOHC DOHC) and Double Over Head Cam (DOHC) designs, can become degraded over time due to heat. 

This deterioration can lead to oil seeping into the spark plugs. During a comprehensive car service Reading, a skilled technician should be able to identify worn-out spark plug O-rings during a spark plug replacement.

Bad Piston Rings

The upper and lower sections of an internal combustion engine’s pistons are equipped with piston rings. The primary function of the compression rings is to safeguard against oil infiltration into the combustion chamber and to eliminate any surplus oil from the cylinder walls. 

Nonetheless, if the piston rings become worn out, they will be incapable of obstructing the flow of oil toward the spark plugs. This may result in the emission of blue exhaust fumes and a pervasive scent of engine oil within the vehicle.

Worn Valve Guides Seals

Vehicles depend on valve guides to effectively regulate air intake into the engine. The valve guides play a crucial role in maintaining the stability of the valves during engine operation. 

However, an inherent drawback is that the valve guide seals tend to deteriorate over time with regular usage. When these seals become damaged, they can not prevent oil leakage into the spark plugs, necessitating their eventual replacement. 

Oil On Spark Plugs Symptoms

Assuming your car isn’t starting, how could you suspect something is wrong with the spark plug? Or, how could you realize there’s oil on the spark plug? Maybe inspecting the spark plug is the only option you have. 

But did you know you can be warned before your car refuses to start due to oil on the spark plug? If not, check the following symptoms and be cautious when any of these signs are noticed. 

  • One of the most noticeable signs is a misfire or rough engine performance, which may be accompanied by decreased power and acceleration. 
  • Additionally, you may observe a reduction in fuel efficiency and increased exhaust emissions due to incomplete combustion caused by oil contamination. 
  • Another symptom is the presence of blue or grayish smoke coming out of the exhaust pipe when starting or accelerating the vehicle. This occurs due to oil leaking into the combustion chamber and being burned along with the air-fuel mixture.
  • Furthermore, if the engine is running roughly or experiencing misfires, characterized by loud sounds often mistaken for gunshots, this could indicate an imbalance in oil levels within the engine. 
  • Lastly, overheating of the engine can occur and manifest as white smoke emanating from under your vehicle’s hood. This smoke serves as an indication that the engine is operating at such high temperatures that it causes rapid evaporation of any water present.

Troubleshooting Car Starting Problems Due To Oil On Spark Plugs

If you notice oil on the spark plug and your car isn’t starting, it doesn’t mean you just rush to a shop and replace the old one immediately. Of course, replacing the spark plug is the simplest and last resort here. 

However, you should try cleaning the oil and check whether the car is starting initially. So, how do you clean oil out of a plug? This is what is outlined below. 

  • Step 1: If you notice oil on the exterior or around the electrode, gently wipe away any visible oil from the surface of the plug using a clean cloth or brush.
  • Step 2: To effectively clean off stubborn oil residue, spray some combustion chamber cleaner onto the spark plug and let it sit for several minutes to loosen the oil deposits. Avoid spraying directly into the port, which may damage other engine components. 
  • Step 3: Following this, use a wire brush with soft bristles and scrub away any remaining oil deposits on both the electrodes and threads; be careful not to damage delicate components.
  • Step 4: After thorough cleaning, assess whether the spark plugs are still functional. If they appear excessively corroded or damaged beyond repair, it is advisable to replace them entirely. However, if they seem salvageable, apply high-pressure compressed air to eliminate debris or excess cleaner before reinstalling them into their respective cylinders.
  • Step 5: Lastly, ensure that any underlying issues causing oil leakage are addressed promptly to prevent a recurrence of oil-contaminated spark plugs. This could involve inspecting and replacing faulty seals or gaskets, correcting excessive blow-by from worn piston rings or valve guides, fixing clogged PCV (Positive Crankcase Ventilation) valves, or rectifying other potential causes identified during troubleshooting.

How to Prevent Oil From Getting On Your Spark Plugs – Expert Tips

To maintain the smooth functioning of your engine, it is essential to prevent oil from getting onto your spark plugs. Here are expert tips to help you prevent this issue and ensure optimal engine performance.

Use high-quality engine oil 

Investing in a reputable brand of engine oil with appropriate viscosity for your vehicle helps minimize the chances of oil leakage. High-quality oils have better additives that can resist breakdown under extreme temperatures or pressures.

Check and replace gaskets regularly 

Gaskets provide a seal between different engine components, preventing oil leaks. Regularly inspecting and replacing worn-out gaskets can significantly reduce the risk of oil contaminating your spark plugs.

Avoid overfilling the crankcase 

Overfilling the crankcase with excessive oil can cause it to be forced into areas where it shouldn’t be, including the spark plug chambers. Always adhere to proper fluid levels indicated in your vehicle’s manual during oil changes.

Maintain proper PCV valve function 

The Positive Crankcase Ventilation (PCV) valve plays a crucial role in redirecting excess pressure and gases from the crankcase back into the intake manifold for combustion. A malfunctioning PCV valve may lead to increased pressure inside the crankcase, causing oil leaks onto spark plugs.

Regularly inspect ignition system components 

Routinely check ignition wires, coils, and boots for signs of wear or damage that could contribute to oil leakage onto spark plugs. Damaged or deteriorated components should be promptly replaced.

Clean and adequately torque spark plug threads 

During routine maintenance intervals, take care when removing and reinstalling spark plugs to avoid damaging them or their threads. Improper torquing can create gaps that allow oil to seep into the chamber.


Is it safe to drive with oil on spark plugs?

It’s not recommended to drive with oil-contaminated spark plugs as it can lead to further damage to your engine and negatively impact its performance.

Is there a way to temporarily fix an oil-soaked spark plug issue?

While temporary solutions like cleaning or drying out the plug may provide short-term relief, a complete assessment or professional intervention is necessary for a lasting resolution.

Should I be concerned if there’s only a small amount of oil on my spark plugs?

Even a small amount of oil on your spark plugs should be taken seriously as it can still impede proper ignition and lead to further engine issues if left unaddressed.

Final Words

So, oil on spark plugs can indeed cause cars not to start. When oil seeps into the spark plug wells and coats the electrodes, it disrupts the electrical current necessary for ignition. This can result in a weak or no spark, leading to engine misfires or failure to start. 

Regular maintenance and inspection of spark plugs can help prevent oil contamination and ensure smooth starting and running of your vehicle. Remember, a small investment in maintaining spark plug health can save you from frustrating breakdowns and costly repairs in the long run.

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