Oil and antifreeze mixture

A breakdown that can bring us many headaches is the mixture of oil and antifreeze or water of the cooling system. If when you go to check the levels of your car, you find a mixture of these two liquids in the expansion bottle, you can start to worry, it may not be a simple fault.

The engine has several ducts inside it. The oil circulates through some of these ducts to grease the engine and through others the antifreeze circulates, which takes care of your cooling. These liquids should not mix and if they do, it means that something has broken. Normally the leak is located in the head gasket or oil cooler. Two very different breakdowns, especially since the first is usually more difficult and expensive to repair.

How to know if there is mixture of oil and antifreeze

Black oil in the expansion tank

To recognize if mixing has occurred, you must open the expansion bottle cap and take a look. if you find one yellowish, brown, or black slimy substance, there will be no doubt that oil has gotten into the refrigeration system. However, it is not always that easy to see. It only becomes such a paste when there is a lot of oil in the antifreeze or water.

In the event that it only mixes a little, you will find some oil stains floating about the antifreeze.. So take a good look and use a flashlight to make sure if you need to. If you still can't see it clearly, use a rolled up piece of paper or a rag and tuck it in. You can then look closely for oil. Whatever you use, the important thing is that it does not leave lint, threads or any residue inside the glass.

High oil or antifreeze level

The next check that is usually done is to check the fluid levels. Two situations can occur depending on the architecture of your engine: the oil level rises or the antifreeze level rises.

• If you see that the antifreeze level has mysteriously risen, it may mean that lubricant has gotten into the cooling system. Especially if it has any oil stains or is turning into the paste that we mentioned before.
• if at check the oil level you see that there is exceeded the maximum marked on the dipstick (without you having added more), it means that the antifreeze has entered the oil passages.

The best way to be sure is to remove some of the oil until it is within the limits of the dipstick. If it goes back up on its own, that's a pretty clear sign of coolant getting in.

Note that when the two liquids are mixed, however, they usually invade both systems. These two situations are just a way of diagnosis. They do not necessarily mean that it is only one liquid that invades the ducts of the other.

Related article:

Antifreeze for the car: what types are there and which can be mixed

What has been broken to cause the mixture of water and oil?

As we have told you, the problem is usually in the head gasket or in the oil cooler. Two breakdowns with a very large price difference, more for the number of workshop hours than for the price of the parts. Another possibility, although less frequent, is that the problem is in the cylinder head itself. Which would shoot up the price of the repair even more.

head gasket

This repair requires many hours and we will have to prepare the pocket. Lifting the cylinder head involves, at a minimum, check the cylinder head itself and fit a new set of gaskets. In addition, it is also advisable to change the screws that fix it to the block.

Problem caused by the oil cooler

Another cheaper option is that the two liquids mixed in the oil cooler. As its name suggests, it is responsible for reducing the temperature of the oil, through the antifreeze that is used to cool the engine.

It has the shape of a small radiator into which both liquids enter. Of course in separate areas, which exchange heat for the high Thermal conductivity of the metal.

Head

The problem we are facing may also be the cylinder head itself. It is not common, but this element can become cracked or deformed due to defects in its manufacture or a continuous overexertion of the engine. Although logically, this will be accompanied by the failure of the head gasket. Likewise, very old engines with frequent temperature changes can also end up with this problem.

Possible faults are:

• If the problem is that the cylinder head has cracked, it will be necessary to change it. The cost of repairs to this part may be greater than the price of putting in a new one.
• If the problem is that the butt has been deformed, perhaps it "just" needs to be rectified. Depending on the model, we can save some money, but it is a job that is done in few workshops in our country.

Whether a replacement cylinder head is to be fitted or just the old one has been repaired, the head gaskets should always be new. In addition to the screws, it is also convenient to replace them.

How do you know if it's a head gasket or oil cooler?

The normal thing is that in the workshop they carry out the pertinent checks. But if for whatever reason you want to make sure of what the problem is, there are two ways to check if you have some mechanical knowledge and some skill.

Method 1: Exclude the cooler from the circuit

Is isolate oil cooler from car cooling system. An operation consisting of:

• drain the oil and antifreeze from the car. Some jobs for which the articles can help you:
  • How to change the antifreeze liquid and clean the radiator
  • How to change the oil in your car
• remove the hoses that carry the antifreeze to the cooler

• connect both hoses to close the cooling circuit without the cooler. Use a short tube of the right size for the sleeves and two zip ties (very cheap items found at any hardware store). Do not forget to cover the entrance and exit of the cooler or at least join them by means of a sleeve so that nothing enters.
• Fill the engine oil again and the cooling system with distilled water. The two articles that we have mentioned before will be useful to you.
• crank the engine until it reaches operating temperature, to see if the oil rises back above the maximum level. If this does not happen, it means that it was the cooler that mixed both liquids.

Two important clarificationsFirstly, every hose you put on needs to be securely clamped, and secondly, reaching the cooler isn't always easy, so if you have to remove parts to get to it, take a good look at how it was so you can leave it the same later. In the following video you can see how it is done step by step:

Related article:

The maintenance of our radiator

Method 2: Howmo know if the cooler oil is damaged

Once you've reached the cooler, the more conventional option is to extract it and check for leaks between the two ducts. This method is the same as the previous one in terms of draining the oil and coolant, but in this case it is a question of decoupling it from the engine. For this you will only need a key of the appropriate size.

You will see that the cooler has two holes for oil and two for antifreeze. There are two main methods without special equipment, with which it is possible to check if there is a fissure that communicates both ducts:

• El First of all is put pressurized air into cooler while submerged in water. It doesn't matter which hole you make it through, you just have to be careful to cover the other hole in the same conduit well. Pushing with your hand may be enough. If you see air coming out of the other system's ducts, it means you've found the problem. Good news, considering the next candidate is the cylinder head or its gasket.
• El second is introduce distilled water through the coolant line and see if it drips out of the oil line. A much simpler method because it requires fewer elements, but it is much less fallible. That is why we do not recommend it. The crack may be very small and the fluid may not leak if extra pressure is not put on it. Remember that the lubrication system works with a certain oil pressure, which would cause it to leak through such a small hole.

As we have mentioned before, if the cooler is in good condition, the problem is most likely in the head gasket or the cylinder head itself. Put the cooler back in its place if you have removed it and take the car to the workshop, because repairing the cylinder head is complex and requires a qualified professional.

However, if you find yourself in this situation, The most reliable thing is to go to a trusted workshop as soon as possible. so that they solve the problem from the beginning there. Failure to do so can have very serious consequences for the engine.

If you want to know more about car mechanics and its maintenance do not miss the articles:

• How to check an air filter
• intake manifold and exhaust manifold
• How to change the oil in your car?
• Remove carbon from your car
• Engine Cooling System Operation.

More information about this model

Peugeot 308

• Plazas 5
• Power 130 - 194 hp
• Consumption 0,8 - 5l/100km
• Assessment 4,5