Car engines are configured that the oil from the engine should never have access to either the coolant or the water.
This is strictly because oil is meant to lubricate all moving components in the engine, the coolant is meant to cool the engine which normally produces heat at high temperatures when it is operating. A vehicle engine is designed in such a way that it has a top cover which is meant to cover the whole engine.
The cylinder head, which is equally part of the cooling system, sits on the engine block, the structure that accommodates the cylinders or combustion chambers. The cylinder head equally forms the ceiling of the combustion chambers. Between the cylinder head and engine block is the cylinder head gasket which will be the target of our discussion.
The cylinder head gasket seals both the cylinder head which contains the engine valves at the topmost components of the engine and the engine block which also houses the pistons and crank shafts at the lower part.
The engine block has two different channel networks bored into it, one channeling the engine oil to where it is needed and the other one doing the same for the coolant/water in the cooling system of the engine.
During the early development of the internal combustion engine, a thin sheet known as the cylinder head gasket was introduced into it. Its purpose was to seal the cylinders to ensure maximum compression and avoid leakage of coolant or engine oil into the cylinders; as such, it is the most critical sealing application in any engine and, as part of the combustion chamber, it shares the same strength requirements as other combustion chamber components.
Whenever oil is found in the engine coolant on inspecting the radiator top-up tank, one will notice that the coolant has formed into a milky colour. It is quite a bad occurrence when the two mix and often means that the gasket has failed to function as needed, creating an internal leakage which could easily damage the engine.
Some of the reasons why engine oil mixes with the coolant include:
- A broken/damaged head gasket. Remember this stays between the block and cylinder head. In case it gets damaged, it will allow oil and coolant to eventually mix.
- A cracked cylinder head due to overheating or an accident. If this is not replaced, it sometimes leads to the mix of oil and coolant. This happens because a cracked head will misdirect the coolant and in the long run it will mix with the oil.
- A damaged engine block since this is the lower part of the engine which houses most of the moving parts that use the oil and if this gets damaged, would lead to the mixing of the fluids.
- Extreme engine overheating, most especially in diesel engines. When engines overheat, they tend to burn and spoils the gasket which in the long run loses its functionality.
- When a vehicle througoesh water that rises to top-of-the-engine level. Sometimes, this water will enter the engine, either through the top cover, or any other open part of the engine. It could also enter through the exhaust pipe, especially whenever one revs the engine while driving through the water.
Bear in mind that whenever there is an oil/coolant mixture, you have to immediately contact a knowledgeable mechanic. If the fault is much, your car may need an engine overhaul, but if it is minor, then the engine is just flushed and the oil and filter replaced to fix the problem.