All vehicles sold in the United States beginning in 1961 arrived equipped with a positive crankcase ventilation (PCV) system that was engineered to help reduce engine emissions. PCV systems have become very complicated on modern engines to reduce oil blowby and meet tightening regulations.
Like all vehicle parts, the PCV can become faulty, and, in doing so, can direct engine oil into the intake. This can cause serious problems for the engine. This article will briefly cover what causes engine oil to enter the intake air piping, throttle body, and intake manifold, and explain what you can do to prevent it from happening.
NOTE: There are no other ways for oil to travel from the crankcase to the intake system other than the PCV system provided on all vehicles.
How the PCV System Works
The main parts of the rotating machinery of your car’s engine are enclosed inside the crankcase and related enclosed camshaft areas. These areas are connected and sealed from the outside environment.
When the engine is running, very high pressures are developed in the combustion chambers will force combustion gases past the piston rings into the crankcase, otherwise known as blowby.
Blowby is unavoidable and a normal occurrence. In a new or low-mileage vehicle, such leakage is relatively small. In an older vehicle, wear to the piston ring will result in a higher rate of leakage.
If the crankcase were not somehow vented, blowby would increase pressure rapidly and eventually cause oil to leak through the engine’s various seals and gaskets.
The vapors produced from this process consist of heated air and water (products of combustion), unburnt fuel vapors, and a small amount of microscopically fine oil droplets suspended in the air/fuel mixture.
The PCV system piping vents these areas to two locations, as well as one port to the air inlet tubing (between the air filter and the throttle body) and one to the intake manifold (between the throttle body and the intake valves).
Both of the inlet locations on the engine receive the blowby vapors. However, the port in the air inlet pipe upstream of the throttle body also allows air to flow back to the crankcase whenever engine vacuum (negative pressure) in the intake manifold occurs.
The PCV valve moderates flow in both directions and regulates the blowby flow rate to minimize its effects on the fuel/air mixture to the cylinders and the combustion process.
In some cars, the piping for the PCV system leads to a port in the air filter rather than one in the inlet tubing. For this type of PCV system, oil in your air filter could also be the result of PCV system issues.
Aside from the PCV connections into the intake of the engine, there is no other source for oil to inadvertently enter the intake system.
Causes of Oil in the Throttle Body and/or Manifold
Many system issues can allow oil to flow through the PCV system piping and end up either in the throttle body or the intake manifold. As you know, the plumbing for the PCV system goes to both of these areas.
In other words, if you see oil evidence either in the air intake tubing before the throttle body, on the throttle body valve and the housing surrounding it, or in the intake manifold, then you have a clear indication of PCV system issues.
#1. PCV Valve Issues.
When there is an issue with the PCV valve, the excessive pressures from the system can force engine oil through the system piping to the air inlet tubing, and then to the throttle body and/or to the intake manifold.
If this is excessive, you will notice smoke when you start your car, which could be blowing out of your exhaust.
A failed PCV valve will likely throw a code to the OBD 2 System on your car, like P053A, P053C, P053E, P0171, or P0174 PCV valve defects. You can check these codes with a code reader tool, at your auto parts store from a sales specialist, or by your mechanic of choice.
#2. PCV System Problems.
If any of the system piping is blocked by sludge or pinched shut for some reason, the system can become pressure trapped, forcing oil to the air inlet tubing or to the intake manifold as discussed earlier.
If you suspect this problem, you can remove and clear the blocked piping.
#3. Aging Engine Issues.
On older engines (greater than 150,000 miles), you should expect to see excess blowby symptoms as part of the engine’s age. Such symptoms potentially include rough idle, rough running, and smoky exhaust.
Out of these possibilities, the least of these will be oil from the system getting into the throttle body and intake manifold. The only way to perform corrective action at this point would be a potentially expensive engine rebuild.
How Serious is this Problem?
In general, this problem will not result in an engine completely stopping. While excess oil entering the combustion chambers may cause engine misfires, may foul spark plugs, may result in excessive carbon build-up on the valves, and may result in a drop in engine power.
These deficiencies will also lead to a decrease in engine efficiency with an increase in fuel run time.
How to Minimize Oil Entering the Inlet Air System
Keep your PCV system clean, so you can perform normal functions. A properly working PCV system is the best option to keep oil from entering the air inlet, throttle body, and intake manifold. If you want the best life for your PCV system:
- Follow your car’s owner’s manual regarding the recommended engine oil type and the frequency of changing oil and filters.
- Use a quality name-brand oil, with 100% synthetic oil the best option to maximize the life of all your engine parts.
- Follow your car’s owner’s manual regarding the replacement of the air filter.