Last Updated on March 22, 2022
If you spend enough time around vehicles, you are sure to witness the occasional odd occurrence, which catches your attention almost immediately. Unfortunately, many of these strange occurrences signify the onset of mechanical issues, which often vary in extent and severity.
One such strange occurrence is the sudden appearance of oil leaking or dripping from your vehicle’s tailpipe. This is not only an odd sight but can be quite alarming, to say the least. In fact, one is often left with far more questions than answers.
In many cases, oil exiting a vehicle’s exhaust is cause for obvious concern and is generally indicative of internal engine issues of one sort or another. This, in turn, presents a significant cause for additional diagnosis.
Read on to learn more about the potential cause of oil coming out of your vehicle’s exhaust, as well as how to address such an issue should it present itself.
What It Means When Oil Is Coming Out of an Exhaust
The only way that oil can find its way out of your vehicle’s tailpipe, is to enter the engine’s exhaust stream, at one particular point or another. However, this can occur in a number of different ways.
Understanding such possibilities assists you in diagnosing and remedying such issues when encountered.
Simply put, oil is introduced into the exhaust stream via the exhaust ports of one or more of an engine’s cylinders. This oil is then displaced into an engine’s exhaust manifold, through the natural downstream flow of exhaust gases.
Oil is then routed rearward through an engine’s exhaust, catalytic converter(s), and muffler(s).
Upon reaching the end of a vehicle’s exhaust stream, this oil looks like black liquid dripping from the exhaust. This, however, is not to be confused with the sight of condensation or water dripping from a black-soot covered tailpipe.
Common Causes of Oil Coming Out of an Exhaust
Oil can enter a vehicle’s exhaust system in several different manners. While some of these failures are more common than others, it certainly pays to understand the complexities of each.
The following are several of the most common causes of oil coming out of your vehicle’s exhaust.
#1 – Clogged PCV Valve
An engine’s positive crankcase ventilation valve is responsible for rerouting a certain volume of combustion gases into each cylinder for further combustion.
However, a clog in this valve can lead to the over-pressurization of an engine’s crankcase, thereby leading to the bypass of seals. As a result, oil can be deposited into an engine’s exhaust tract.
This can also cause oil to appear in your intake manifold, throttle body, or intake piping.
#2 – Blown Head Gasket
A blown head gasket can also be responsible for the inadvertent delivery of oil into the engine’s exhaust stream. In proper functioning order, an engine’s head gasket separates each of a vehicle’s fluids from one another.
The head gasket also prevents fluid loss into an engine’s combustion chambers. However, a failed head gasket can allow oil to make its way directly into one or more cylinders.
#3 – Worn Valve Guides
An engine’s valve guides prevent lubricating oil from passing beyond a cylinder head’s valve stems. But like any component, an engine’s valve guides are susceptible to wear over the course of time.
This presents an opportunity for oil to seep by into an engine’s exhaust, often presenting a bluish-grey smoke as a byproduct. In severe cases, oil can be seen passing from an engine’s exhaust.
#4 – Broken Piston Rings
Each of an engine’s cylinders features piston rings, which move up and down with the movement of the cylinder’s piston itself. These rings serve a vital function, by preventing excess combustion loss.
However, these piston rings also prevent oil from making its way into the combustion chamber. When one or more of a piston’s rings become broken, oil loss into an engine’s exhaust tends to be rapid.
#5 – Cracked Block or Head
Structurally, an engine consists of a block and one or more cylinder heads. These main structural components must remain in peak condition, in order for engine performance to be maximized.
However, cracks within cylinder heads or an engine block do occur on occasion, often resulting in the loss of engine oil into combustion spaces. When this occurs, oil is carried downstream, until eventually exiting a vehicle’s tailpipe.
#6 – Damaged Piston
In certain rare cases, the head of one or more of an engine’s pistons can become damaged, allowing for the displacement of oil into an engine’s combustion chambers.
A certain amount of this oil is then burnt, while all remaining oil is expelled downstream into an engine’s exhaust manifold, via open exhaust valves. If severe enough, a portion of this oil will be pushed out of a vehicle’s exhaust pipe.
Is It Safe to Continue Driving?
Under most circumstances, a vehicle should be driven to the nearest service center and removed from service upon the first signs of oil leaking from its exhaust. This is due to the fact that such issues are often indicative of much larger problems, including instances of internal engine damage.
Therefore, the continued operation of a vehicle in this state can actually result in further damage. This, in turn, could necessitate the more extensive expenditure of both time and effort in order to take corrective action.
Extensive loss of engine oil into a vehicle’s exhaust also risks potential fire.
Can Oil On an Exhaust Catch Fire?
Oil can indeed catch fire on a vehicle’s hot exhaust. This tends to be most prevalent when this oil collects on or around an engine’s exhaust manifold, where existing exhaust tends to be the hottest.
But in most cases, the oil will solder or smoke, before actually creating an open flame. Smoke that is produced will typically be bluish-grey in color.
Additionally, the superheated engine oil will generally create an easily identifiable burning odor. This odor tends to be evident even to those seated within a vehicle’s cabin, especially if such fumes are scavenged through a vehicle’s fresh-air ducts.