Oil In Coolant Reservoir: Its Presence And What It Means


Well, even if you haven’t been familiar with the details, it is considered as common sense that your oil of the engine should never really mix with the water or any coolant, and if it does so, something is going wrong with your vehicle that needs your attention.

But why is it considered so and what does happen when oil mixes with the coolant? What does it mean?

To answer these questions, let’s first understand the basics of engine functioning, which will also help you to identify, which type of problem might be persisting in your vehicle’s engine.

What Do the Oil and Coolant Achieve?

Oil and water shouldn’t come together in your vehicle. This is because oil, as we all know, is a lubricant that is being used to lubricate the different movable parts of your car’s engine. And as the engine drives the vehicle, it generates an immense amount of heat due to the energy being produced.

To cool this down, coolants are used, which keep the temperatures of the engine steady and under control. In your car, truck, or any other four wheeler vehicle, the engine is designed in quite a peculiar manner so that it can be covered completely with a top that would protect the engine from foreign agents.

1. The Structure in Detail


Via : http://www.doityourself.com/stry/how-a-coolant-reservoir-works#b

The cylinder shaped head in this system happens to be a part of the cooling system rests on the block of the engine. The block of the engine is the structure, which has several different combustion chambers or cylinders. The cylindrical shaped head forms the upper portion or ceiling of the chambers where combustion and ignition take place.

Between the engine block structure and the cylinder-shaped head rests the head gasket (cylinder) – the central part of your vehicle’s engine that requires attention when oil is getting mixed with the coolant. This head gasket has a paramount function as it seals both the cylinder head and the engine block that contain engine valves and pistons along with crankshafts respectively.

The engine valves are located in the top part whereas the pistons and crankshafts are located at the bottom.

  • Two different and distinct channel networks are bored into your vehicle’s engine block. One of those networks is the engine oil while the other is for the coolant.
  • The engine oil’s network directs the oil to the parts of the engine where it is required whereas the same is achieved for water or coolant inside the engine’s cooling system.
  • ​Observe your combustion engine if possible. Here, a thin sheet called head gasket was introduced during the early development stages.
  • ​The objective of the head gasket in the internal combustion engine is to ensure highest possible compression and avoid any or all type of leakage of the liquids inside (engine oil and the coolant), onto the cylinders.
  • ​This was achieved by sealing off the cylinders with the head gasket. The cylinder head gasket, therefore, happens to be one of the most significant applications of sealing in a vehicular engine.
  • Being a part of the combustion chamber, the cylinder head gasket has the same physical strength specifications and requirements as the other components in the combustion chamber.

2. Mixing of Oil and Coolant

oil in coolant

The necessary conclusion that can be drawn from the mixing of oil and water in your vehicle’s engine is that the seal of the engine has broken off, and thus the head gasket has terribly malfunctioned or broken down. Usually, the radiator top up a tank or the reservoir tank shows the mixing of the oil and coolant. We find the coolant to have transformed into a milky substance or a brown mass.

This means the cylinder head gasket and the internal engine require your attention because due to the failure, an unknown internal leakage has been induced, which has caused the mixing of the two liquids. Is it dangerous? Yes, indeed because it can cause damage to your engine and thus, wreck your vehicle.

However, it wouldn’t be wrong to say that this phenomenon does not usually take place in the latest car or vehicular models all of a sudden. Overworking of the engine, improper servicing, accidental heavy impact and age-related vehicle weariness are the common causes of mixing of the engine oil and the coolant.

3. The Common Reasons – Why Does It Happen?

Common Reasons

Via : http://m.wikihow.com/Check-the-Fluids-in-a-Car

Engine’s head gasket failing to perform its function is just the common guess of every vehicle owner and novice, but there might be other specific reasons as well, which might have caused this malfunction to happen. According to the leading mechanics and vehicular engine experts, some of the reasons why your oil is ending up in the cooling reservoir are as follows:

  • The basic, broken or damaged cylinder head gasket is the leading cause of the mixing of the two fluids. In the case of any light or heavy damage to the gasket, the oil and the coolant will be eventually allowed to mix.
  • Damage to the cylinder head to is one of the main reasons of the mixing to take place. The cracked or damaged cylinder head might be a result of overheating, overuse of the engine or a heavy impact in the accident. After this damage, there is a dire need to get the cylinder head replaced as soon as possible because if this is not achieved in due time, the damaged cylinder head would not correctly direct the coolant after some time, which might then get mixed up with the engine oil.
  • ​Damage to the engine block is uncommon, but it too can lead to the mixing of the oil and the coolant, leading you to find the oil in the coolant A damaged or cracked engine block happens to rest in the lower engine part that contains several movable parts (that use oil). Slight damage to the engine block too causes the oil to mix with the coolant in the coolant reservoir.
  • ​Overheating or overuse of the engine is not good for every part of the engine and can cause many different malfunctions, one of them being the oil flowing into the coolant reservoir and the eventual mixing of the two liquids. Extreme overheating of the engine tends to destroy the head gasket, which as mentioned, allows internal leakage of the engine oil.
  • Excess of water into the engine that rises to the top might also lead to the mixing of the two fluids. Vehicle often passes through water and this water might enter the engine through exhaust pipe as well, damaging the flow and functioning of the engine, causing the oil to leak and water to mix with the engine oil.

4. Handling the Mixing

If you have opened the reservoir or the radiator top and observe that the coolant-oil mixture has formed, and the vehicle has started to behave in an odd manner, it is time for you to take immediate action. However, with little knowledge of the vehicular engine’s functioning, you can’t do much other than cleaning up. Hence, you should be an immediate call for experienced vehicle mechanic who is not only knowledgeable but has the extensive experience of identifying such kinds of problems to give a proper solution.

Depending on whether the problem is extreme or small, the mechanic might give you different solutions. For example, if the problem is small and can be simply taken care of by adequate cleaning or change of a little part in the engine, or can be corrected with a change in the filter, the same would be done, and your vehicle would be a god to go. If the problem, however, happens to be large and has been persistent, you might require an engine overhaul or replacement of several parts of your engine to rectify the issue.

Why Is It So Important?

Well, handling the mixing of the two liquids is important not because it is causing wastage of the coolant or the engine oil, but because it can cause even more severe damage to the engine of your car and lead to even bigger problems. It has been reported that poor use and maintenance of the vehicles often tends to put the engine of your vehicle at a substantial risk of getting damaged, irrespective of the extent.

If the damage takes place and the mixing of the two liquids also happens, the engine will not function properly – neither it will be able to drive the vehicle nor will it cool down efficiently after overheating and overuse. This might, in turn, causes sparking, fire or even small explosion in the engine of your vehicle, putting your car and your life in danger. Thus, it is crucial to counter this problem as soon as possible.


oil in car coolant

Oil in the coolant reservoir can be a huge issue or a small leakage result, which can be rectified in time if action is taken immediately. As it can turn into a serious problem in the future, it is highly advised that you consider getting proper leak tests done for your engine by an experienced mechanic so that your vehicle life gets extended and you are saved from probable severe damages in the future.

Photo Credit:

  • http://www.audi-forums.com/b5-forum/61911-oil-coolant-reservoir-please-help.html
  • http://honda-tech.com/honda-civic-2001-2005-78/oil-my-coolant-reservoir-2707594/
  • http://www.powerstroke.org/forum/6-4-motor-problems/798546-oil-coolant-tank.html
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