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What really happens to your motorcycle when you overfill engine oil

A harley davidson engine showing ill effects of overfilling engine oil
6864 Views Aug. 12, 2020, 1:17 p.m.

The engine is the heart and soul of the motorcycle. Whatever latest model or superbike you own, if the engine oil maintenance is not correctly and timely performed, it can ruin your riding experience. In a motorcycle engine, different motor parts work together to convert the fuel energy into mechanical energy, thus creating friction when they come in contact.


To ensure smooth running and prolonged durability of your motorcycle engine, a routine engine oil change is very important. As per the amount specified in the owner manual, bikers must periodically change the engine oil as it not only ensures the healthy running of the motorcycle engine but also increases the running life of your motorcycle.

Depending on the size of the engine, every bike requires a varying amount of engine oil and the same can be easily seen in your bike’s owner manual. Now when you or your mechanic has changed or refilled the engine oil, you often notice some of these below changes in the functioning of your motorbike when the engine oil has been filled over its capacity, i.e., when the engine oil is overfilled.

  • Oil leakage
  • Smoky exhaust
  • Fouled spark plug
  • Signs of smoke from the exhaust area and the engine bay
  • Too much noise from the engine

In the owner manual, it is clearly stated: “Not to Overfill”. Unfortunately, there is no clear explanation of what will happen when the engine oil is overfilled? What harm will it have on my bike? In this later section of the blog, we will explain to you what happens when you accidentally overfill the engine oil above the stated limit and the risks it carries for your motorcycle. 

Overfilling the engine oil can cause serious damage to your engine, but if you have filled the oil few millimetres above the maximum sign, there is no need to worry. This is because of the fact that the engine oil reserve of the motorcycle is designed to hold some extra engine oil which compensates for the fluid expansion that occurs due to hot conditions. Adding any more engine oil over this limit is bad for the engine. 

When you add too much oil, the pressure on the crankcase increases. At the output shaft, this pressure might be well enough to rupture the oil seal if your engine’s crankcase would not have been vented via a rebreathable circuit. During normal operating, when the air inside the crankcase heats and cools, the rebreathable pumping balance the pressure inside the crankcase. When you have overfilled the engine oil, the extra oil will go towards the crankshaft, and as the crankshaft keeps rotating at high speed, this oil gets mixed with air and becomes foamy causing a smoky exhaust. This works as a bad lubricant for the engine and due to which the oil is not pumped efficiently. Over time due to the weak oil pumping, the engine can even get locked up.

engine-oil oil-leakage smoke spark-plug engine-noise
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