Oil in Intake Manifold (Causes, Symptoms and Fixes)

Oil in Intake Manifold

The air/fuel flows into the intake manifold are the lungs of internal combustion engine design. When the intake is not ideal, problems arise that must be attended to. Most issues that detract from the vehicle performance are involved with the intake system or the fuel system. Oil in the intake manifold is one of those problems.

Intake Manifold

The intake manifold, also referred to as the inlet manifold, is a system of a phenum and runner tubes that are mounted on the internal combustion engine. Air enters the vehicle through the throttle body and continues on to the intake manifold. The manifold is the last destination for the air before it enters the cylinders. The manifold distributes the air/fuel mixture in even amounts for each cylinder. When the camshafts opens the valves of the cylinder, each cylinder receives the same amount of air. The variable valve (VVT) solenoid, also referred to as the oil control valve, also helps the engine breathe and is attached to the near the cylinder head block.

When the air enters the intake manifold, sensors measure the pressure and the temperature of the air. These measures are used to create the air/fuel ratio. The throttle position sensor is one of the most critical components of the air intake system; and when it is not working properly there are problems within the intake manifold.

When it is working as it should, the throttle body controls the air/fuel flows into the engine. Most cars are designed with one throttle body; however, there are some with more than one. The throttle body is a tubular unit located in the air intake between the air filter and intake manifold which is where the response comes from pressing the gas pedal. All of these components must work together to keep the engine running.

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Causes of Oil in Intake Manifold

Of course, oil does not belong in the intake manifold. When small amounts of oil, or an oil mist makes it way to the intake manifold, it will get burned up in the combustion chamber and any residue is managed in the catalytic converter. If excessive amounts of oil do make their way there, it is a problem. How the oil makes its way to the intake manifold is pretty straight forward:

Positive crankcase ventilation – This is one of the most common causes of oil in the intake manifold. Most newer vehicles use a Positive Crankcase Ventilation (PCV) system (view on Amazon) to manage the pressure and remove gases and blow-by from the crankcase.

The positive crankcase ventilation (PVC) valve releases the built up pressure between the oil pan and the intake manifold

When the positive crankcase ventilation is bad, it causes buildups of engine sludge and oil leaks. It will also cause the vehicle to consume more fuel. If blue smoke is coming out of the exhaust when you accelerate, the problem could be that the positive crankcase ventilation has gotten stuck. When this happens, air, oil, and gas are mixing together inside the engine. The mixture will cause the blue smoke to escape from the exhaust.

Blocked oil passages – This is also one of the most common reasons for oil in the intake manifold. When the normal passages for the oil become blocked, the oil redirects and flows through the positive crankcase valve hose into the intake manifold.

Manifold system leaksWhen the air/fuel flow is not properly balanced, it causes problems with throttle body pressure. Vacuum leaks can form in many areas to include the throttle body evaporative emissions system and the intake manifold. The engine control unit (ECU) configures the ratio of air to fuel in the engine. When there is a leak, the configuration of the mixture is not accurate. The most common areas where these types of leaks occur are in the intake manifold, vacuum hoses (view on Amazon), or the blow-off valve.

Gasket or seal leaks – Internal combustion engine uses several types of gaskets and seals to secure the liquid flows, such as flows of coolant or oil. Many of these gaskets and seals are located inside the intake manifold and the throttle body. Over time, the seals may dry up and leak with disrupts the security of the oil flows. The head gasket is a special seal that is located between the engine block and cylinders.

Oil and water – Water often enters the crankcase in the blow-by from combustion. The entrance of water promotes emulsion formation which does go well with crankcase oil. The crankcase breathes because of the condensation. The crankcase will sometimes sweat. The oil is consumed faster and soon, there is a mixture of oil, water, and dirt.

Dirty air filter – The air filter stops much of the debris in the air from entering the engine. The filter becomes dirty or worn over time which means it can no longer filter out things like oil and debris. The engine can no longer suck in enough air. This means the engine will choke, running rich, with too much fuel and not enough air. When this is the problem, the car’s performance decreases as it requires more fuel, reduces the horsepower, emits smells of gas, and causes misfiring.

Engine sludgeEngine sludge is a major cause of the clogged and blocked passages for the oil flows. This often which often happens in cars that have not had regular oil changes. The more the oil is used, the more the accumulation of trash. Together, the heat and trash oxidate the oil, which changes the structure to a gel-like, sticky substance that is so thick, things begin to attach to it that won’t fit through the oil filter.

Poor Maintenance – If you regularly have problems with your vehicle or you’re experiencing problems with the oil system, chances are you don’t maintain your vehicle often. The key to avoid problems within your vehicle along with oil problems is to properly maintain your vehicle.

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Symptoms of Oil in Intake Manifold

Oil in the intake manifold is not appropriate; however, it is very common in older engines. Don’t minimize the problem. The sensors on your car will react to the disorder which will manifest in different ways. Here are the most common symptoms of oil in the intake system:

Check engine light – Problems with the PCV or thermostat will activate the check engine light on your dash. OBD2 codes will be thrown for the problems. The check engine light will also activate when problems arise that are associated with the problem. You can use a professional OBD2 scanner (view on Amazon) to diagnose this problem.

Oil light activated – If the oil light is activated, oil in the intake manifold could be a part of reason. When you first start your car, the oil gauge needle should start out at high, as oil pressure is highest when its temperature is cold. Most newer vehicles have an oil pressure warning light attached to sensors. The warning light could also mean that there is not enough oil pressure.

Engine failure – If a larger amount of oil is puddling up in the intake manifold as opposed to an occasional light spray, this is a serious problem. If engine oil passages clog up with sludge, this is also a serious problem. These problems may cause the engine to run roughly. Engine failure because of sludge buildup is also very common problem.

What to Do About Oil in Intake Manifold

As much as people may tell you the oil in the intake is no big deal, it doesn’t belong there. You want your car to run at tip top shape. You also want your engine to last for a long time. So, if you have oil pushing up into the intake valve, the problem needs to be addressed. If you think you have this problem, follow these steps:

Replace the air filter – Dirty air filters will definitely contribute to oil in the intake manifold. Manufacturers recommend changing the air filter once a year or every 12,000 miles. Usually the filter is inspected during an oil change. However, if you haven’t been getting an oil change the filter can become really dirty really fast. The cost of the replacement is really cheap. Most times, it will be less than $100. If you can do it yourself, that is even better.

Check the oil pan – Raise your hood and check the engine to see if there are any brown or black buildups of residue on the engine. There may even be intermittent spots of sludge along the sides of the vehicle. Then, remove the oil cap off and use a flashlight to check your oil pan (view on Amazon). If you have a considerable engine sludge problem, you will see some sludge in the oil pan.

Increase the crankcase temperature – Combustion generates heat and some byproducts that get into the crankcase and contaminates the oil. The crankcase oil temperature control can help prevent or dampen engine sludge. It increases the quality of engine lubrication, reducing engine wear. It also improves fuel economy and engine performance.

Use crankcase ventilation – Positive crankcase ventilation recycles the gases to the intake manifold where they will eventually return to the cylinders for combustion. When the engine accelerates, air pressure in the intake manifold increases. This suction reduces the amount of blow-by to the cylinders.

Clean it up – You can use a use a chemical engine sludge remover to the clean the problem areas yourself. This is the simplest way to remove engine sludge. Simple add the remover to the buildup, let your vehicle idle for 10 minutes. That will give the remover time to solvate the sludge and draw it into the oil. Then, change the oil. You can try having the PVC cleaned to correct the problem before trying more expensive solutions.

Regular maintenance – Regular oil changes and tune ups are a great idea. Your owner’s manual will tell you what should be serviced and when. Having the oil changed and possibility having something flushed is preventive maintenance as well as a remedy. Keeping the vehicle serviced as recommended by the manufacturer will prevent passage blockage and sludge problems.

Take it to a repair shop – Most people who work on cars know how to identify problems like oil in the manifold gasket. If you are not one of those who are familiar with working on cars, it’s better to let a certified professional handle it. Take your car in to a repair shop and let them know your concerns. They have seen these types of problems before and they know the best way to fix them. Take your car in for regular servicing as well, it the blockage and sludge would not be overlooked. Get that problem fixed and drive safe.

Safety First

Remember safety first. Driving a car with any time of mechanical problem is irresponsible. You now know how to recognize engine sludge, what it can do, and what to do if you have that problem. Don’t drive your car once you have discovered the sludge. Have your vehicle serviced by a professional so that you can drive safe.

Job Guthiri is a freelance writer with 3 years of experience writing for Motorsrun and other established automobile outlets. His focus and key interests are Tacomas and maintenance. Read our Editorial Guidlines and Fact Checking process.