Skip to content
Do you always find the oil level mysteriously dropping on the dipstick, but see no oil leaks under the car? Every time you open the hood, a strong burning smell hits your nose, and blue smoke puffs out from the exhaust during cold starts... Worst of all, the mechanic says it’s 'burning oil,' but you don’t know where the oil went. Should you spend thousands fixing the engine or keep driving nervously?
Don’t worry! This guide will explain why this happens, How to check the problem and the Repair options.
How to Tell if Your Car Is Burning Oil (Key Symptoms)
If the problem of your car burning oil isn't dealt with in a timely manner, it may cause serious damage to the engine. But how can you tell if it's normal wear and tear or a malfunction? Here are 7 key symptoms and self-check methods.
1. Blue Smoke from the Exhaust Pipe during Cold Start
Blue smoke is a typical sign of a car burning oil. Under normal circumstances, the exhaust gas of a car should be colorless or slightly white with water vapor. However, when the car is burning oil, the exhaust gas will be obviously blue. This is because the engine oil enters the combustion chamber and participates in the combustion. The unburned engine oil produces blue smoke which is then emitted.
2. Excessive Oil Consumption
In addition to visually checking for blue smoke, oil consumption is the easiest to notice. Under normal circumstances, within one maintenance cycle of the car, the decrease in the engine oil level is within a reasonable range. If you find that the engine oil level drops significantly in a short period of time (and there are no signs of external oil leakage), or you need to add engine oil frequently (record the scale on the oil dipstick and check the consumption every 1,000 kilometers driven), it is very likely that there is a problem of the car burning oil.
3. Unusual Smell of the Exhaust Gas
The smell produced by the burning of engine oil is very different from the smell of normal fuel combustion. A pungent burnt smell is one of the most typical symptoms of a car burning oil.
4. Decrease in Engine Performance
If the car has weak acceleration, slower speed increase, insufficient power when climbing hills, or there are abnormal noises in the engine, all these may indicate the possibility of the car burning oil.
5. Abnormal Spark Plugs
Under normal circumstances, after the spark plugs have been used for a period of time, their color is brown or tan. If you find that the spark plugs are black or oily, it means that engine oil has seeped into the cylinders.
6. Abnormal Carbon Deposits in the Combustion Chamber
By checking with an endoscope, you can see that the top of the piston is covered with black carbon-like carbon deposits. In severe cases, it may even block the valves.
7. The Engine Fault Light Is On
Burning oil causes the exhaust gas to contain an excessive amount of hydrocarbons, which triggers an oxygen sensor trouble code (such as P0172 for a rich air-fuel mixture).
Burning Oil vs. Oil Leak Symptoms
If there is no oil stain on the ground but the engine oil keeps decreasing, it usually indicates that the problem lies inside the engine, and there is a 90% possibility that it is the engine burning oil. The following are the differences between burning oil and oil leakage.
| Symptoms | Burning Oil | Oil Leak |
|---|---|---|
| External Oil Stains | None | There are oil stains under the engine, on the oil pan or at the seals. |
| Smoke from the Exhaust Pipe | Blue smoke comes out during cold start or acceleration | No special smoke |
| Speed of Oil Consumption | Relatively slow, with a consumption of > 0.3 liters per 1,000 kilometers and no external leakage | May be relatively fast, depending on the leakage point |
| Condition of Spark Plugs | Black oil sludge adheres to the spark plug electrodes or threads | Spark plugs are dry and have no oil stains |
| Unusual Smell | Burnt smell of burning oil | Smell of fresh engine oil |
| Common Causes | Piston ring wear, aging of valve stem seals, PCV valve failure | Aging of the oil pan gasket, rupture of the crankshaft oil seal, loose oil drain plug |
| Maintenance Cost | Relatively high. It may require a major overhaul of the engine, such as replacing the piston rings. | Relatively low. It may only require replacing the oil pan gasket. |
| Emergency Treatment Suggestions | Avoid driving for long distances and have it checked and repaired as soon as possible to prevent cylinder scoring. | Add engine oil immediately and check the leakage point to prevent the engine from running out of oil. |
Methods of Distinguishing Burning Oil and Oil Leak
Step 1: Lay a piece of white paper under the parking space and check if there are any oil drops the next day.
Step 2: Observe if there is blue smoke coming out of the exhaust pipe during cold start (unique to burning oil).
Step 3: Check if there are obvious oil stains in the engine compartment (a sign of oil leakage).
Related Reading: How to Reset and why Your Change Oil Light comes on
Why is my car burning oil but no leaks?（Common Causes）
1. Aging of Valve Stem Seals
The aging of valve stem seals is a common cause. The valve stem seal is a key component to prevent engine oil from seeping into the combustion chamber. If the valve stem seal hardens and deforms, the engine oil will flow into the combustion chamber along the valve stem and burn to produce blue smoke during cold start.
2. Wear or Sticking of Piston Rings
The wear or sticking of piston rings is a core mechanical failure. Piston rings are responsible for scraping off the engine oil on the cylinder wall and maintaining a seal. If the piston rings are stuck or have an excessive gap due to carbon deposits, wear, or improper installation, the engine oil will directly enter the combustion chamber and participate in the combustion.
3. Failure of the Positive Crankcase Ventilation (PCV) Valve
The PCV valve is responsible for regulating the pressure in the crankcase. If it is blocked or damaged, it will cause an imbalance of pressure in the crankcase, forcing the engine oil vapor to enter the intake manifold and participate in the combustion.
4. Engine Overheating
Engine overheating may cause damage to the seals of the cylinder head or valve cover, allowing the engine oil to enter the combustion chamber and be burned off. This situation is usually accompanied by the problem of abnormal temperature rise of the engine.
5. Fuel Dilution
Using low-quality fuel or fuel containing too much water may cause the engine oil to be diluted, thus increasing the consumption of engine oil. In this case, the engine oil may be burned off, but there will be no obvious oil leakage marks outside the car.
6. Wear or Scratches on the Cylinder Wall
Scratches are formed on the cylinder wall due to long-term wear or cylinder scoring, resulting in the piston rings being unable to seal effectively, and the engine oil directly entering the combustion chamber. This can be confirmed by inspection with an endoscope.
How to Diagnose the Problem
Diagnosing oil burning requires a systematic approach. Start with simple visual checks, then move to advanced tests if needed. Here’s how to pinpoint the exact cause.
- Check if there is blue smoke coming out of the exhaust pipe during cold start.
- Check if there is serious carbon deposition on the spark plugs and if there is engine oil on the spark plug threads.
-
Endoscope Inspection for Internal Diagnosis
As a non-destructive testing tool, the endoscope can be used to check the carbon deposition on the top of the piston and whether there are scratches on the cylinder wall when diagnosing the problem of the engine burning oil. Especially when there is no external leakage, it can help accurately locate the internal faults of the engine.
Remove the spark plugs and insert the endoscope probe into the engine. Focus on observing the carbon deposition on the top and the scratches on the cylinder wall.
A thick layer of carbon deposition means that the piston rings are stuck.
Longitudinal scratches on the cylinder wall mean that the piston rings need to be replaced. -
Using an OBD2 Scanner to Detect Oil Burning
Plug ANCEL OBD2 scanner tool into your car to read error codes.
Check for PCV Valve Fault Codes: P052E/P052F indicates abnormal crankcase pressure; P0172 indicates a rich air-fuel mixture, which may be caused by the engine oil contaminating the combustion chamber.
Analyze Oxygen Sensor Data: If the sensor voltage stays high (above 0.7V), oil is burning in the engine. -
Measure the Cylinder Pressure to Judge the Sealing Performance of the Piston Rings
The normal cylinder pressure range is (120-180 PSI for gasoline engines. If it is lower than 100 PSI, it indicates wear of the piston rings). -
Component Replacement Verification
Replace vulnerable parts such as the PCV valve and valve stem seals, and observe whether the engine oil consumption improves.
How to protect your car from burning oil?
-
Optimize driving habits. Avoid idling for a long time or accelerating suddenly to reduce the high-temperature working conditions of the engine.
Use high-quality engine oil with good quality and moderate viscosity. - Replace worn parts, such as valve seals, piston rings, etc.
- Regularly check the engine oil level and the quality of the engine oil, and detect problems in a timely manner.
- Pay attention to the cleaning of the fuel oil circuit. Regularly use fuel additives to clean carbon deposits.
FAQs
Does burning oil mean I need a new engine?
Not necessarily. In most cases, there is no need for a major overhaul. Instead, the problem can be solved by replacing the piston rings or valve stem seals. However, in severe cases, it may be necessary. For example, if the cylinder wall is severely worn or the clearance between the piston and the cylinder wall exceeds the standard. Such situations usually occur due to long-term neglect of the problem of the engine burning oil, and a major overhaul or engine replacement is required.
Is it bad to drive a car that burns oil?
Whether you can continue driving depends on the degree of the engine burning oil and the amount of engine oil. If the exhaust pipe only emits blue smoke briefly during cold start, you can drive for a short distance, but you need to add engine oil. If blue smoke is continuously emitted during driving, the power drops significantly, or the engine oil warning light comes on, you must stop the car immediately. Severe oil burning may cause the engine to have cylinder scoring, and the engine will be completely scrapped.
