Engine Oil: What happens if you run out of it?

Motor oil
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Engine oil can be considered one of the most important operating fluids in the engine. So what happens if your car runs out of engine oil?

Does this always result in fatal damage, or can the engine be repaired afterward? We'll get to everything, but first, let's talk about the main function of the engine oil.


Engine oil function

Engine oil is a technologically very complex product used as a lubricant in combustion engines of cars. The engine oil fulfills the function of lubrication, cooling, cleaning, and sealing but also protects against corrosion.

We classify engine oils according to the production method into mineral, semi-synthetic, and synthetic. In addition, engine oils can be classified by viscosity and performance. Various other factors and requirements are placed on engine oil, but that is a topic for another article.

Why does engine oil disappear from the engine?

The most common cause of oil loss is that the engine consumes (burns) oil. There can be several reasons for excessive oil consumption, such as a turbocharger that has worn bearings or a damaged seal. However, the cause can be worn piston rings, cylinders, cylinder liners, or pistons.

For instance, the blue smoke from the exhaust may alert you that your engine burns oil. However, the loss of oil may not only be caused by a worn engine component but also by the clumsiness of the driver, for example, when he punctures the engine oil pan.

Oil warning light

Unfortunately, some old engines have no warning light on the dashboard to alert you to a lack of engine oil, so you must regularly check the oil.

In more modern cars, the oil warning light lights up when there is a lack of engine oil, but some are equipped with an oil level indicator that graphically displays the amount of engine oil on the scale every time the key is turned to the second position.

What happens if the engine runs out of engine oil?

If the engine runs out of oil, it means that the engine will not be sufficiently lubricated nor cooled, and there is a risk of seizing and fatal damage to the entire unit. Usually, however, the engine does not run out of all the engine oil, but there is so little left that it cannot sufficiently lubricate individual parts and transfer heat from them.

There's a widely spread misconception that if the engine runs out of oil, the engine will stop immediately. This is simply not true. If the engine runs out of oil, it can run for a while before it stops completely.

It all depends on the driving style. For example, running the engine at high revs will take quite a short time before it seizes. On the other hand, when driving calmly, the engine can run for a relatively long time without an oil filling.

Lack of engine oil: What are the symptoms?

At the same time, the lack of engine oil does not manifest itself immediately, and the symptoms come gradually. The first symptom is increased engine noise and a rattling metal sound.

The second symptom is engine overheating and significant loss of power. However, if you do not stop the engine even after these symptoms, it will eventually seize and stop.

Engine seizing occurs due to insufficient lubrication and heat removal from the engine components. In such a case, the connecting rods, crankshaft, piston rings, cylinders, and pistons will suffer the greatest damage.

Damage due to lack of engine oil

The crankshaft

The crankshaft, connecting rods, and bearings are most often damaged. The crankshaft uses bearings for storage in the engine block but also for connection to the connecting rods, which must be constantly lubricated and cooled with engine oil.

When the oil film is lost, there is high thermal stress on the bearing but also a significant increase in friction, which ultimately causes the bearing to seize.

If only the crankshaft's main bearings seize, the engine will only stop. In such a case, the engine can be run by replacing the crankshaft bearings or, in the worst case, by replacing the entire crankshaft.

In such case, the engine can be repaired by replacing the crankshaft bearings, or in the worst case, by replacing the entire crankshaft.

Seized connecting rod bearings

Connecting rods

However, if the connecting rod bearings seize, a much worse situation will occur than just stopping the engine because the connecting rod bearing tends to crack. In this case, the connecting rod will be disconnected from the crankshaft, which can break through the engine block and fly out of it, especially at higher engine speeds.

No one will repair the hole in the engine block, so you have no choice but to replace the entire engine. In most cases, however, replacing the entire engine rather than an engine overhaul is cheaper. If it is not an expensive car, you can take it straight to the scrapyard because the repair would be higher than the price of the whole car.


Therefore, all the consequences of the engine seizing are fatal, and their removal is costly. We cannot argue that oil is an indispensable liquid for the engine, without which it could not function, or actually could, but only for a minimal time.

Short video animation showing how engine oil works