Oil consumption is one of the most common problems. It can occur on vehicles with high mileage as well as on new cars. Let’s figure out whether this phenomenon is normal, whether something needs to be done about it, and what issues might arise.
First, let’s define what actually counts as oil consumption. If you notice that the oil level has dropped by more than 1 L per 1000 km (about 0.25 gal per 620 mi), that can already be considered a problem. A loss of 0.1–0.2 L per 1000 km (0.025–0.05 gal per 620 mi) is a normal case because some oil inevitably burns during operation. There are cases where the engine design allows for even greater oil consumption (for example, the 13B‑REW engine), but those are more of an exception than a rule and are related to the engine’s architecture.
Now let’s look at the general reasons for oil consumption. Oil can be lost through:
- External oil leaks
- Oil entering the combustion chamber (often called oil burning)
External leakage is easy to spot with a visual inspection. If you see significant oil leaks or oil stains on the surface where the car is parked, that signals that intervention and repair are needed because over time a lot of oil could seep out. This type of fault can be resolved by tightening the fasteners (bolts, nuts) or replacing seals/gaskets that may have dried out over time. If external leakage occurs regularly and at different places (for example, you fixed the problem in one spot but it started leaking elsewhere), then you should pay attention to increased crankcase pressure. High oil pressure can be caused by inappropriate oil with excessively high viscosity, contaminated oil passages, stuck pressure relief valves, or wear of compression rings, which leads to increased crankcase gas pressure.
Oil entering the combustion chamber (burning oil) is exactly the problem people refer to when they say the motor is consuming oil. This can be caused by two factors. The first is oil entering the combustion chamber due to worn valve stem seals. The second is wear or seizure of the piston ring and cylinder components (piston–cylinder group). Let’s go through each in order.
Oil entering through the valve stem seals occurs as a result of a loss of seal between the seal and the valve stem. It is very easy to determine that oil is indeed entering through the valve stem seals. There are actually two methods.
- Method 1: After a short drive, remove the spark plug and check whether there is oil on its threads. If there is, there is a 99% probability that oil is leaking through the valve stem seals (for various reasons – it ripped, tore, or broke). The idea of this method is that oil from the cylinder head seeps onto the plug threads.
- Method 2: Start the car, keep it running at idle for 10 minutes, then slam the accelerator pedal. If you get a burst of blue or dark-blue smoke once and afterwards the exhaust becomes clear, that indicates a problem with the valve stem seals. Why does this method work? The idea is that during engine operation, a certain amount of oil accumulates in the cylinder head for the lubrication of mechanisms. When the accelerator is suddenly pressed (or during sudden throttle opening), a sharp drop in pressure (a strong vacuum) is created in the cylinder, leading to a strong draw of the fuel-air mixture.
However, if the valve stem seals are worn or in poor condition, the high vacuum created in the cylinder during the intake stroke draws oil through the faulty seals. That is the logic behind this method.
Repair associated with replacing valve stem seals is not expensive or time-consuming.
Burning oil in the combustion chamber that occurs due to wear or seizure of piston ring and cylinder components manifests differently. It may also be diagnosed by two methods:
- Method 1: Similar to the valve stem seal test, after a short drive remove the spark plug and look at its electrode. If there is dark brown/black carbon deposit on the electrode side of the plug, this indicates that either the valve stem seals or the piston rings have problems, or there is significant wear in the cylinder.
- Method 2: With the engine running (preferably idling), suddenly press the gas and hold for a few seconds. If blue or dark-blue smoke continuously comes from the exhaust pipe, this signals issues with piston rings, pistons, or cylinders.
Repair associated with piston ring and cylinder problems is quite expensive and time-consuming.
In summary, oil consumption by a car engine can be either a normal phenomenon (depending on engine design) or a problem. That’s why it’s important to carefully analyze what’s happening, stay attentive, and draw correct conclusions.