Fuel dilution of the engine oil is a problem that faces many modern combustion engines. Also known as “crankcase dilution” it is a process where fuel is able to enter the crank case and mixes with the engine oil . It is a process that occurs roughly 8 times per 1000 rpm for each cylinder, and whilst it occurs in every engine, it is a factor that contributes a significant amount of wear to the engine. It is also one of the main reasons why periodic oil testing is performed for many engines, as it inevitable that every engine will experience it. However it is far more prevalent in diesel engines and owners of Diesel engines need to be awear of it and be extra diligent with routine oil changes.
The Causes of Fuel Dilution in Engine Oil
There is not one cause of fuel dilution within engine oils and this is a reason why it is such a common occurrence within engines. However, the main cause is through a process called blow-by. This occurs because most seals are not perfect (nor are the cylinders perfectly rounded), or there is an opening through the cylinder crosshatches, and this causes the migration of fuel and exhaust gases into the areas where the oil is used. This often happens in the region between the piston rings and the cylinder bore.Other factors include leaking of the fuel injectors, incomplete combustion of the fuel, low engine temperatures, long periods of idle time and frequent short-distance driving.
COLD STARTS
Cold starts i.e. engines that have not yet reached their optimum operating temperature. Colder engines have a lower combustion efficiency than engines which are at the ideal operating temperature, and this causes the fuel to ignite further on in the compression stroke. This can also cause the fuel coming out of the injector to stick to the walls of the cylinder. Once the fuel is stuck to the sides, it will drain down tot he sump by slowly enter the oil system by being scraped off by the piston rings and entering the crankcase.
Poor Maintenance
Fuel dilution within an oil system happens slowly. So, when some oil becomes contaminated with a small amount of fuel, the effects are very minimal and won’t affect the performance of the oil (or the engine in general). That is if it isn’t allowed to build up—that is when issues start to arise as large amounts of fuel dilution will affect the performance of the oil and the engine. Therefore, regular maintenance in the form of regular oil checks and changes can stop fuel dilution from presenting any adverse effects, but there can be catastrophic consequences if these basic services are skipped.
As well as regular oil checks and changes, checking the fuel injector nozzles can help to reduce the occurrence of fuel dilution—as dirty nozzles can prevent the fuel from atomizing correctly, and in turn, prevent the fuel from combusting efficiently. unfortunately this is a costly exercise as injectors need to be removed and tested by third party experts.
This is often only needed if the vehicle is displaying symptoms such as high oil viscosity, misfires and other mechanical faults.
There are quite a few concerns with fuel dilution which affect the performance of the oil and the engine in general. Over time, excessive dilution can lead to a significant amount of wear, and ultimately, the failure of the engine. The biggest issue that arises from fuel dilution is the lowering of the oil’s viscosity, as fuel has a much lower viscosity than the oil, which in turn can cause the oil-fuel mixture to adopt a viscosity lower than it is designed for. This causes the oil to possess less-effective lubricating properties and causes the strength of the oil film to be reduced, which increases the amount of wear on the cylinder liner and the bearings.
In most cases this issue is more prevalent in Diesel engines. The ramifications of it are easily mitigated with routine oil changes. Leaving a diesel engine oil change for too long often results in high level of oil dilution which in turn causes the oil to be far to thin and not lubricate the engine well enough causing major internal engine failure. Change your diesel engine oil every 10,000 kms no matter what and you are unlikely to experience these problems.
