Why Oil Is On Spark Plugs Threads & Wells : Causes & Quick Fixes

Oil On Spark Plugs

Oil on the spark plugs can be a sign of a serious problem that needs to be addressed as soon as possible. Because oil on the spark plug of any internal combustion engine indicates the damaged condition of the engine. Oil getting on the spark plug hinders the combustion of fuel in the engine, which badly affects the performance of the engine. Therefore, if oil is coming on the spark plug of your vehicle, you should investigate the reason in time. There can be many reasons for oil getting on the spark plug.

In this article, we will discuss in detail the causes and symptoms of oil on the spark plugs, knowing how to prevent additional damage to the engine.

Why Oil Is On Your Spark Plugs – Causes

The main causes of oil on spark plugs are damage piston rings or worn valve seals. Additional causes may include faulty PCV valves, leaky O-ring seals, engine overheating, engine oil overfill, cylinder head cracks, or excessive engine wear.

Let us know in detail the causes of oil on spark plugs so that you can diagnose this problem in time and easily.

1. Worn Valve Seals


Valve seals are an extremely important component in the head of any internal combustion engine, preventing oil from entering the engine’s combustion chamber during valve movement. If an engine’s head valve seals fail, it causes oil to leak into the cylinders and spark plugs, and the engine produces white smoke, affecting engine power and fuel mileage. Does matter.

2. Worn Piston Rings

Damage piston rings

The piston rings in any internal combustion engine are designed to form a seal between the piston and the cylinder wall, preventing oil from entering the combustion chamber and forcing oil back into the chamber.

If the engine’s piston rings are worn or damaged, they can send oil into the combustion chamber when the engine is started, which can cause the oil to spark. It is impossible to fix this problem without overhauling the engine.

3. Damage Valve Cover Gasket

valve cover gasket

Damaged valve cover gaskets can also be the cause of oil getting on the spark plugs of an engine. The valve cover gasket in the engine seals the top of the engine and prevents oil from leaking out.

But if the valve cover gasket is damaged or fails, engine oil can leak on the spark plugs. However, these oil leaks take longer to reach the bottom of the spark plugs, and leaking valve cover gaskets can also see oil leaking onto the engine head and block.

4. PCV (Positive Crankcase Ventilation) System Issues

pcv valve

In fact, the PCV system in any internal combustion engine is designed to regulate the flow of gases between the crankcase and the intake manifold, helping to channel the gases formed in the crankcase to the air inlet. But if the PCV valves become clogged or corroded, the excessive crankcase pressure of gases can force oil into the combustion chamber, causing oil on the spark plugs.

5. Overfilling Engine Oil

If the engine is overfilled with oil, adding too much oil to the engine can result in overpressure, which can result in oil leaking out of the engine spaces and into the combustion chamber and spark plugs. Because filling excessively while the engine is running may force the oil to leak. That’s why you should never fill the engine with more oil than the vehicle manufacturer’s recommendation.

6. Cracks Cylinder Head or Engine Block


In many cases, cracks in an engine’s cylinder head or engine block can cause oil to leak into the combustion chamber and reach the spark plugs. A cracked cylinder head or block is a serious problem that cannot be fixed without rebuilding or replacing the engine. Cracks in the cylinder head or block can cause many engine-related problems, such as engine overheating, misfiring, and exhaust white smoke.

7. Damaged Spark Plugs Tube Seal

Oil on spark plugs can also be caused by damaged spark plug tube seals. These seals prevent oil leakage in the spark plug tubes. If these seals are damaged, oil can seep into the tubes and spark plugs, causing the engine to emit white smoke and misfire. In many cases, the spark plugs may short out over and over again.

8. Excessive Engine Wear

When a vehicle’s engine ages and accumulates high mileage, the internal components of the engine may wear out, causing oil to leak into the combustion chamber and cause oil to settle on the spark plugs. Is. Therefore, when the engine is old, it needs to be taken care of from time to time.

9. Engine Overheating

engine overheating

Sometimes the engine overheats due to any reason; the excessive heat of the engine can cause the gaskets and seals to wear out, which can lead to oil leakage on the spark plugs. Engine overheating is a condition that can damage the entire engine and sometimes lead to an engine seizure.

Symptoms Of Oil On Spark Plugs

  • Engine Misfires & Backfires
  • Exhaust Blue Smoke
  • Reduce Engine Performance
  • Engine Vibration & Jerks
  • Difficult Engine Starting
  • Low Fuel Mileage
  • Gas Smell From Exhaust

Why Does Oil Get On Spark Plug Threads?

Oil leaking onto the spark plug threads can be caused by a bad valve cover gasket or spark plug tube seal. The gasket and spark plug tube seal prevent oil leakage from the engine’s valve cover and cylinder head. If any of these components are damaged or worn, they allow oil to seep onto the spark plug threads during engine operation, which can impair spark plug performance and reduce engine efficiency.

Additionally, oil on the threads can make it difficult to remove or install spark plugs. In many cases, oil on the spark plug threads can cause exhaust white smoke.

Why Does Oil Get On Spark Plug Wells?

Oil leakage into the spark plug wells is caused by a worn valve cover gasket or O-ring. In many cases, worn pistons or worn valve guides can also result in oil leaking into the spark plug wells. Oil leakage into the spark plug wells is a serious problem, affecting the performance of the spark plugs and causing the engine to misfire and produce white smoke, affecting engine power performance.

How To Fix Oil On Spark Plugs?

  • Gather enough tools: You may need a torque wrench to unscrew the spark plugs.
  • Disconnect Battery: First, let the engine cool down and disconnect the battery to prevent any accidental electric discharge.
  • Remove the spark plug wires and coils: To remove the spark plugs, first carefully separate the spark plug wires/ignition coils from the spark plugs.
  • Remove Spark Plugs: Carefully open and pop out the spark plugs with a socket wrench and note their position.
  • Inspect and Clean: Check spark plug threads and wells for oil contamination. Clean the area around the spark plug wells with a cloth. You can use spark plug cleaner for this.
  • Replace Gaskets and Seals: Replace old valve cover gaskets and spark plug tube seals with new ones. Because damaged valve cover gaskets and spark plug tube seals can cause oil leaks in spark plugs.
  • Install new spark plugs: If the old spark plugs are worn out and not in working condition, replace them with new plugs of the correct type and gap.
  • Reconnect the spark plug wires and coils: Reconnect the spark plug wires or ignition coils to the proper spark plug.
  • Reconnect Battery: Reconnect the battery.
  • Start the Engine: Next, start the engine and monitor for engine misfires or oil leakage.
  • Check for Leaks: Keep an eye on the spark plug wells for any signs of oil leakage. If you find that the leak continues, double-check your work and make sure all components are properly attached and tight.

Note that if your engine has badly damaged piston rings, head valves, guides, and seals, cleaning the spark plugs or replacing them is a temporary solution. In many cases, cracks in the engine cylinder and block are the cause of oil getting on the spark plugs, in which case the option is to overhaul the engine or replace it.


Q. Can oil damage the ignition coil?

Yes, oil can damage the ignition coil. Oil leakage from valve cover gaskets can damage the ignition coil, or oil moisture can impair its functioning.

Q. Is it better to clean or replace spark plugs?

If a spark plug is not cleanable or the plug shows unusual signs of damage, a replacement is a better option than cleaning it.

Q. Do spark plugs affect acceleration?

Yes, bad spark plugs can affect acceleration because they cause incomplete combustion, which leads to engine misfires, jerks, and reduced engine power. Acceleration hesitation, and struggle can be felt due to bad spark plugs.

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