An annoying problem that drivers may encounter is the smell of burnt oil they feel in the car. In addition to not being able to drive the car with that smell, this symptom may indicate some problems.
The smell of burning oil in the car can indicate engine and transmission issues. The most common causes are leaking valve cover gaskets, cylinder head gaskets, oil seals, but also problems in the air system like a clogged air filter.
Where does the smell of burning oil come from?
The smell of oil usually enters the car cabin through:
- the air ducts of the ventilation system, which are located above the engine compartment. As the engine warms up, this becomes more noticeable.
- the cabin fan when you turn it on and the recirculation mode is turned off.
- door seals;
- pedal assembly.
The persistent odor of burning oil in the car interior clearly indicates a technical problem with the engine, or, in lesser cases, issues with the transmission and attachments. These sources can be found in the engine compartment and that bad smell can be felt especially when the engine warms up.
If you don’t feel the smell coming from the engine compartment, then it’s worth looking under the car because the odor can travel with the help of the exhaust system. It can come from the transmission or other parts located under the car.
The result of this bad smell of burning oil is felt because the oil gets on the cylinder’s hot walls, on the exhaust system, and/or components related to it. Most often this is due to engine problems.
Oil leaks typically produce a stronger odor as the engine warms up and the oil begins to burn out. Symptoms appear almost immediately after starting the engine if oil enters the exhaust system. During rain or snowfall, the ingress of moisture with oil or reagent particles from the road surface to the exhaust pipe may be the source of the temporary odor.
You can determine the exact location with the help of some symptoms. If you feel the smell while driving with the windows open, and the smell appears or intensifies when the interior ventilation is turned on and disappears after a short time when the recirculation mode is activated, the smell, most likely, comes from the engine compartment.
If you feel the smell with the windows open and goes away after you close all the windows, then the smell comes from under the car. When oil is ejected directly through the exhaust system, you can see blue smoke coming from the exhaust pipe in addition to the smell.
Smell of burning oil coming from the engine compartment
There are some methods to check exactly where the smell is coming from. If you suspect that the smell is coming from the engine compartment, you can find out by inspecting it visually, by finding traces of oil on the engine.
In the best scenario, the oil traces may be there because of recent maintenance. When the oil was changed, traces of oil got on the engine by mistake and were not cleaned. This also is available for transmission oil.
Other causes imply a leaky valve cover, leaking crankshaft, and camshaft seals, or clogged or bad crankcase ventilation system, usually a pipe, and a failing cylinder head gasket. These issues can be difficult to solve, that why is best to go to a repair shop for a proper investigation.
For example, if oil leaks from under the valve cover gasket, the mechanic can try to tighten the cover fasteners. If this does not help, the gasket needs to be replaced.
If oil comes from the crankshaft or camshaft seals, this could indicate increased pressure in the cylinder block caused by a clogged crankcase ventilation system or wear of the oil seals themselves.
The seals must be replaced if the oil level is normal, the air system is not clogged, and there are no signs of excessive pressure (no smoke comes out when the oil filler cap is opened).
If oil leaks are due to a bad cylinder head gasket, things here are a little bit hard to deal with and it is advisable to go to an authorized repair shop.
Talking about issues with a cylinder head gasket, not only oil, but also coolant, including the mixing of the two in the cooling system and cylinder block, may leak.
The smell of coolant and white smoke from the exhaust, the presence of oil stains in the antifreeze, and a change in its level in the expansion tank all indicate a malfunction. A broken gasket must be replaced as soon as possible.
Smell of oil coming from under the car
Like in the case presented earlier, traces of oil indicate some problem, but to find them, you need a pit or an elevator to see under it. These oil leaks most often care coming from the transmission input shaft oil seal or the crankshaft oil seal. The exact cause can only be determined when the transmission is removed.
Moreover, the oil sump may have leaks due to a worn gasket, insufficient tightening of the drain plug, or deformation of the o-ring. To eliminate the cause, worn parts must be replaced.
For a better precision of finding out the issue and to distinguish the types of oil involved, we can say that transmission fluid is darker in colour, has a sulphur smell, and the oil film is thinner than motor oil.
If you didn’t find oil traces in the engine compartment and under the car, check the exhaust. A strong odor, oil marks, and blue smoke can indicate a serious issue.
The cause could be worn piston rings, worn valve stem seals, or problems with the turbo in turbocharged vehicles. A thorough engine diagnostics is required to eliminate the cause.
Oil marks not only can indicate a problem with the seals, gaskets, engine and transmission, but driving with that bad smell can be very unpleasant.
Some solutions point to easy repairs like replacing seals, but diagnosing and fixing oil leaks can become very difficult and challenging, even for a professional. That is why is best to opt for an authorized repair shop when you want to fix oil leaks to get the best results.