Car engine oil smell and colour – what does it mean?


Car engine oil keeps your car healthy – but what does it mean when it looks milky, black, or when it smell burnt, sweet or of petrol?  Here motoring journalist and expert Pete Barden takes a look at what changes to the smell and look of your car's engine oil could mean. 

Engine oil can deteriorate over time and risk damage to your motor. As part of this, the look and smell of oil can change can change – and drivers can use these changes identify potential problems before they become more serious and damage the car’s engine.

We look at the meaning of milky oil, and what other strange appearances and smells mean to your car's health.We look at the meaning of milky oil, and what other strange appearances and smells mean to your car's health.  (Credit: Pxhere)

Colour of car engine oil

The colour of engine oil is a good and easy-to-check indicator of its condition and how effective it will be when driving. Fresh engine oil is generally golden brown, but as it is used, it darkens to a darker brown or even black colour. While these stages are normal, there are times when the appearance can signal a problem.

Here’s what to look out when it comes to engine colour. To check, just leave your car standing for an hour, then remove the dipstick – check your manual or Google if you don’t know how to do this?

Milky oil

If your engine oil is milky, it means there is likely to be water or coolant in it. This could be caused by a leaking head gasket, a cracked engine block, or a damaged oil cooler. If you notice milky oil, it's important to get your car checked out by a mechanic as it could be a serious – and expensive – problem to sort out.

Thick and sludgy oil

If the engine oil is thick and sludgy, it could signal that the oil has not been changed for a very long time. The sludge is typically made up of of dirt, debris, and old oil that has broken down over time. This can lead to poor engine performance and fuel economy. Regular oil changes are a simple way to keep performance and economy at their best.

Metallic filings in the oil

If you notice metallic particles in the engine oil, it could be a sign of metal wear or damage to engine parts. This could be due to various factors such as old age, high mileage, or poor maintenance. If you notice metal particles in the engine oil, you should get your car checked by a mechanic as soon as possible.

Smell of car engine oil

The smell of engine oil can also indicate potential problems. Fresh engine oil has a neutral odour, but as it gets older, it can develop a burnt smell. This is normal, but there are times when the smell of engine can warn you of a developing problem.

Burning smell

If you notice a burning smell from your engine oil, it could be a sign of a leak. The oil may be leaking onto hot engine parts, such as the exhaust system, causing it to burn and produce a strong odour. This can lead to engine damage and should be investigated immediately.

Sweet smell

A sweet smell coming from the engine oil could mean you have coolant leak. The coolant may be leaking into the engine oil, which because of the chemicals in it can cause lubricant to smell sweet. This can lead to serious engine damage – get on the phone to you mechanic asap.

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Fuel smell

If your engine oil smells of petrol or diesel, then you should get it checked out. There are many reasons why oil can smell of fuel, from small amounts of natural mixing, to bigger problems such as damaged or badly worn pistons.

Another problem is, that fuel can thin down the oil, making it lose its viscosity – effectively cutting its ability to lubricate moving parts in the engine. This can lead to serious damage that will not be cheap to remedy.

If the smell persists, get your mechanic to take a look and see if it is a problem or just normal.

How to prevent problems with oil and engines

Regular maintenance and check-ups can help prevent potential problems with your car engine oil. Understanding the colour and smell of your engine oil can help you identify potential problems early and take corrective action before they become serious.

If you notice any unusual smells, colours or consistency in your engine oil, it's important to get your car checked by a mechanic as soon as possible.

Regular oil changes can help prevent potential problems and keep your car running smoothly for years to come.

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Author: Pete Barden:

Twitter: @pete_barden

Pete Barden is a qualified journalist who has written and produced for publications including The Sun (, New Statesman Media Group, Whatcar? ( Stuff Magazine (, Fastcar Magazine (, Maxim Magazine and UK broadcast stations within the Heart network (Formerly GCAP). Pete specialises in motoring and travel content, along with news and production roles. You can find out more about Pete Barden on LinkedIn.

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