Why does oil get into the intake manifold or throttle body?
Since 1961, vehicles sold in the United States have been equipped with crankcase ventilation (PCV) systems designed to reduce engine emissions. In modern engines, PCV systems have become more complex to reduce oil blow-by and meet stricter regulations.
However, if the PCV fails, engine oil can leak into the intake tract, causing serious problems. This article explains why oil gets into the intake line, throttle body, and intake manifold and how to prevent it. Note: Aside from the PCV system present in all vehicles, there is no other way for oil to enter the engine’s intake system from the crankcase.
How the PCV system works
The major rotating mechanical components of a car engine are contained in the crankcase and its associated enclosed camshaft area. These areas are connected to each other and sealed off from the outside world.
When the engine is running, very high pressure builds up in the combustion chambers, forcing combustion gases past the piston rings and into the crankcase. This is called blow-by. Blow-by is a normal phenomenon that cannot be avoided. On new or lightly mileaged cars, such leakage is relatively minor. As cars get older, this leakage occurs more frequently due to worn piston rings.
If the crankcase is not vented in some way, the blow-by will quickly build up pressure there. In the not-too-distant future, this will cause oil to leak from various gaskets and sealing rings in the engine. The vapors produced in this process include heated air and water (by-products of combustion), unburned fuel vapors, and small amounts of fine oil droplets suspended in the air-fuel mixture.
The PCV system piping vents these fumes at two points: the intake line between the air cleaner and the throttle body, and the intake manifold between the throttle body and the intake valve.
Both intake points on the engine absorb blow-by gases. However, an opening in the intake pipe in front of the throttle plate also allows air to flow back into the crankcase when engine suction (negative pressure) develops in the intake manifold.
PCV Valve
The PCV valve regulates flow in both directions, regulating the blow-by flow rate to minimize its effect on the mixture and combustion process in the cylinders. On some cars, the PCV system lines connect to a port on the air filter instead of a port on the inlet hose. In this type of system, oil in the air filter can also be caused by a PCV problem. Aside from the PCV connection to the engine intake, there are no other ways that oil can accidentally get into the intake system.
Causes of Oil in the Throttle Body or Intake Manifold
Various system problems can cause oil to enter the throttle body or intake manifold through the PCV system lines. Keep in mind that the PCV system lines run through both areas.
In these situations, oil will be noticeable in either the intake hose in front of the throttle body, the throttle valve and surrounding housing, or the intake manifold. If an inspection finds oil in these areas, it’s a clear sign that there is a problem with the PCV system.
1) PCV Valve Trouble
If there is a problem with the PCV valve, excess system pressure can cause engine oil to flow through the system lines into the intake hose, throttle body and/or intake manifold. If this problem occurs excessively, you will see smoke coming from your car’s exhaust.
A faulty PCV valve may also send a code to your car’s OBD 2 system. Codes such as P053A, P053C, P053E, P0171, or P0174 may indicate a problem with the PCV valve. These can be checked using a code reader, either by a sales professional at an auto parts store, or by your preferred mechanic.
2) PCV System Troubles
If any of the system lines become clogged with mud or pinched due to wiring problems, the system can become pressurized and force oil into the intake lines or intake manifold as mentioned above. If you suspect this is the problem, you can remove and clean the clogged lines.
3) Engine Aging Troubles
As engines get older (over 150,000 miles), they can develop symptoms of excessive blow-by. These include rough idling, rough running, and exhaust fumes. The least of these problems is oil leaking from the system into the throttle body and intake manifold. Only an expensive engine overhaul will help in this situation.
How serious is this problem?
This problem usually won’t shut down your engine. However, too much oil in the combustion chamber can cause misfires, fouled spark plugs, excessive carbon buildup on the valves, and loss of engine power. These defects can also lead to poor engine performance and, ultimately, increased fuel consumption.
This prevents oil from getting into the intake system.
The following steps will help keep your PCV system clean and functional. A properly functioning PCV system is the best way to keep oil out of the air intake, throttle body, and intake manifold. To optimize the life of your PCV system:
– Follow your vehicle manufacturer’s recommendations for engine oil type and frequency of oil and filter changes.
– Use a quality brand of oil. 100% synthetic oils are preferred to extend the life of all engine components.
– Follow your vehicle manufacturer’s recommendations for changing air filters.