Why Does New Engine Oil Have a Bad Smell?

[MollyLee]

New engine oil having a bad smell may indicate the use of counterfeit or inferior products. Precautions for adding engine oil are as follows: 1. Choose engine oil based on the requirements of the engine. Do not use high-grade oil in lower-grade engines or low-grade oil in high-grade engines; select oil that matches the engine. 2. Multi-grade oil should be preferred. Multi-grade oil offers advantages such as fuel economy, long service life, and high efficiency, providing better protection for the engine. 3. The oil level should be slightly below the mark on the dipstick and not overfilled. Excessive oil not only increases the rotational resistance of the crankshaft but also reduces the engine's output power. Moreover, excess oil can enter the combustion chamber and participate in combustion, leading to oil burning, blue smoke emissions, and increased fuel consumption. 4. Select oil with different viscosities based on the engine's operating condition. If the engine is in good condition and the seasonal temperature is low, use oil with lower viscosity. If the engine is severely worn and the seasonal temperature is high, opt for higher viscosity oil. 5. Always drain the existing oil completely and clean the lubrication system thoroughly before adding new oil to avoid mixing different types.

[VanMackenzie]

It's indeed unsettling to detect a foul smell from newly replaced engine oil. I recently encountered a similar situation, and after investigating, it could be due to several reasons: the most common is the oil itself being problematic, such as purchasing a substandard product or improper storage leading to expiration. Inferior oil might be mixed with waste oil, and that sulfur-like stench is particularly noticeable. Another possibility is improper filling, where residual old oil mixes in, especially if the car previously burned oil—carbon deposits can contaminate the new oil. Even more concerning is coolant leaking into the oil, as the sweet smell of coolant mixed with oil turns sour and foul. Continuing to drive under such conditions can damage the engine. I recommend not driving immediately; instead, open the engine hood and smell the filler port. If something seems off, contact a garage promptly for an oil change and inspection. If you suspect counterfeit oil due to cheap purchases, be sure to file a complaint.

[StSkylar]

Many car enthusiasts have complained to me about the foul smell of new engine oil. It's most likely due to poor oil quality—unscrupulous manufacturers might recycle and refine used oil, which contains high levels of sulfur compounds, resulting in a strong odor. If it smells like rotten eggs, that's almost certainly the case. You also need to be careful during oil changes. If the mechanic isn't professional and the filling tools aren't cleaned properly, mixing in old oil or contaminants can immediately cause off-odors. Additionally, if there's an internal leak in the engine, such as a blown head gasket allowing coolant to seep into the oil, it can produce a vinegar-like smell—this issue can range from minor to serious. Whenever I buy engine oil myself, I only choose reputable brands. After changing the oil, I drive a short distance and then check the dipstick—if the color is clear and there's no strange smell, I can rest easy.

[SanEmma]

New engine oil with unusual odor often stems from the oil itself. Genuine oil shouldn't have a strong foul smell—if present, suspect counterfeit first. Small workshops using inferior base oils and additives may produce pungent chemical odors. If the smell is brief upon startup, it might be new additives volatilizing under high temperatures, fading soon. However, persistent odors usually indicate contamination, such as mixing with other fluids or long-term heat degradation. I once handled a case where a reversed oil filter caused restricted flow, overheating, and odor—a minor issue fixed by timely correction.

[Margot]

Don't ignore the strange smell of new engine oil, as it often indicates minor issues. Poor-quality oil itself tends to have an odor, especially when mineral oil is mixed with impurities, emitting a strong rubber-like smell. During maintenance, you should also supervise the process. If the oil pan isn't cleaned thoroughly, residual used oil can directly contaminate the new oil, resulting in a noticeable burnt odor. More seriously, a coolant system leak can cause pink antifreeze to mix with the oil, producing a sour smell, which may lead to lubrication failure. I recommend that car owners stop driving immediately if they encounter this situation, take photos of the oil, and consult the seller or repair shop for verification. Don't hesitate to address it to prevent minor issues from turning into major repairs.