Oil on Motorcycle Spark Plugs: Why and What to Do About It

spark plug oiled

While oil on many engine components is a good thing, it is a no-no on the spark plugs. If the spark plug electrodes get oiled up, there will be problems in spark generation and hence in the fuel ignition.

So why do spark plugs get oil on them? Spark plugs get oiled up if the piston rings in the engine are worn-out, or the valves are damaged, or the engine oil is of poor quality.

The quick fix here is to remove the spark plug, clean it and refit it back. The long-term solution, however, is to address the issue at hand and fix the cause. Be it replacing the piston rings, and valves or changing the engine oil.

Let’s deep dive into each of these details and what steps need to be taken further.

Why do spark plugs get oil on them?

For spark plugs in car engines, the reasons can be multiple. It can range from a cracked valve cover to a damaged spark plug o-ring to worn-out piston rings.

For motorcycle spark plugs, however, the reasons are rather limited. There is no cause from a cracked valve cover or a damaged o-ring. The main reasons for a motorcycle spark plug to get oiled up boils down to these reasons below.

Reasons

The first and foremost reason for a motorcycle spark plug to get oiled up is because of damaged piston rings.

Piston rings separate the fuel mixture in the combustion chamber from the engine oil flowing in the crankcase. As a result, piston rings act as a barricade between the fuel and the oil flowing within the engine.

Now, if the piston rings get damaged, the oil in the crankcase moves along the walls of the inner cylinder and enters the combustion chamber through the gap between the piston and the cylinder.

Once the oil enters the combustion chamber, it oils up the spark plug and the chamber. That’s how the spark plug gets oiled here. The key thing though, the oil will burn along with the fuel and exit through the exhaust most of the time.

The second reason, worn out valve seals. The valve seals ensure that the oil does not flow into the combustion chamber and at the same time make sure the valves are functioning well.

If the valve seals get damaged or worn out, the engine oil will start leaking into the combustion chamber and start coating the spark plug with oil.

The third reason is low quality engine oil. If the engine oil quality is poor and has too low of viscosity, then it can slip past the piston rings and enter the combustion chamber. This is despite the piston rings working well.

As a result, the thin poor quality oil will enter the combustion chamber and coat the spark plug with oil.

Lastly, in two-stroke engine motorcycles, if the gasoline is mixed with too much oil, then the spark plug gets oiled up as well.

This is because the gasoline and the oil are mixed in a two-stroke engine. Quite unlike in four-stroke engine where the fuel and the oil flow separately and never to be mixed up.

So, if the oil is added too much, then again the oil flows to the spark plug and makes it coated with oil.

Symptoms

Now that we know the reasons for the spark plug to get oil on it, let’s look out for the symptoms.

  • White smoke from the exhaust: Oil entering the combustion chamber will not only oil the spark plug but also get burnt along with the fuel. The burnt gases exit the engine and flow out through the exhaust. If you see white smoke from the exhaust, then that’s oil leaking into the chamber and oiling up the spark plug.
  • Misfiring engine: When the spark plug gets oiled up, it will fail to ignite the fuel consistently. As a result, expect the engine misfires. You might even have trouble starting the engine if the oil has coated up the electrodes too much.
  • Fuel economy drops: Oil on spark plug prevents regular spark generation. So, the fuel mixture in the engine will not burn completely since the spark plug is not igniting the fuel mixture properly. As more and more fuel exits without combustion, more the fuel economy drops.
  • Lack of power and acceleration: This is in continuation with the previous points. Irregular spark ignition by the spark plug because of the oil coats on the electrodes lead to poor engine performance and hence, poor acceleration and power generation.

Apart from these, you will also notice other symptoms which are common to the symptoms of a spark plug gone bad or fouled.

Oil on spark plugs is bad? why so?

I think the symptoms section would have made it clear why oil on the spark pugs is a bad thing. Still, let’s discuss in detail why a spark plug should not get oiled up.

First, an oil-coated layer on the spark plugs, especially on the center and the ground electrodes hinders spark ignition in the engine. The electric spark that is generated from the center electrode and reaches the ground electrode is prevented by the oil coating these electrodes.

As a result, there is a lot of interruption in the spark generation and in turn, the ignition of the engine fuel mixture. You will soon start noticing the drop in the engine and the motorcycle’s performance.

There will be starting problems. As mentioned in the symptoms, there will be engine misfires, low fuel economy and mileage, and lack of power and acceleration.

In addition, there can be engine rattling noises, low engine oil levels, and engine overheating as well.

What needs to be done

Now that we are familiar with the causes and the symptoms of spark plugs getting oiled up as well as understanding why oil on the plugs is a bad thing, let’s deep dive into what needs to be done.

Inspection

First, we need to confirm that the spark plug is indeed coated with oil. For that, you need to take out the spark plug and examine it.

The spark plug is located on the cylinder head clearly visible in the motorcycle engine by the distributor cable end. All you need to do is remove the cable and take out the spark plug.

Spark Plug

Once you have removed the spark plug, check the condition. If it’s blackened or worn-out, it doesn’t matter whether there is oil or not, the spark plug has gone bad and needs to be replaced anyway.

If, on the other hand, the spark plug is in good condition but is oiled up heavily, time to address the oil situation in the spark plug.

Solution

The oil on the spark plug is a symptom of another problem usually. The piston rings might have worn out, the engine has low viscosity or the valves are worn out.

As a short-term fix, you can clean up the spark plug, remove the oil layer, and install the spark plug back into the engine.

But the real fix is you need to check the oil leaking source and fix it. Poor quality engine oil is the easiest of all and can be done easily by draining out the engine oil and replacing it with new high-quality oil.

The other two, valve replacing or piston ring replacement are tedious and time-consuming. It will be best if you take your motorcycle to the dealer or a service shop and let them handle it.

Preventive measures

Prevention is damn better than cure. While an oiled-up spark plug does not sound like a big nuisance, wait for the service shop guy to say the piston rings need to be replaced. Then surely you will agree prevention is far better.

First, use high-quality engine oil. Don’t cheap out on this. Poor quality engine oil is not just bad for spark plugs but for the entire engine as well. In no time will the engine start overheating and start to perform poorly.

Second, examine the condition of the spark plug periodically. The best frequency is every time you take your motorcycle for servicing. Ensure that the spark plug condition is inspected at least once every six months.

Third, check the condition of the valves regularly. Again, this inspection can be done whenever you take your motorcycle for servicing. Ensure the valves and their o-rings are in the best condition to function.

And at last, make sure the piston rings are fitted right and there is no engine blowby. Engine blowby allows the fuel to leak along the cylinder walls as well as allow the oil to move into the chamber. It will also damage the piston rings fast.

With these preventive measures which are mostly periodic maintenance that can be done whenever you take your motorcycle for servicing, the spark plug will be in a good condition to perform well.