What colour should engine oil be?
Engine oil should be amber or light brown when new, gradually turning darker as it circulates through the engine. While some colour change is completely normal, unusual oil colours can be an early warning sign of serious mechanical problems.
Checking your engine oil colour is one of the simplest forms of car maintenance and can help you spot issues like coolant leaks, internal wear, or overdue servicing before they cause expensive damage.
This in-depth guide explains what different engine oil colours mean, when dark oil is normal, and when you should stop driving immediately.
Table of Contents
What Colour Should Engine Oil Be When New?
Fresh engine oil is typically:
- Amber
- Golden brown
- Clear and translucent
This colour allows the oil to flow freely and properly lubricate critical engine components such as pistons, camshafts, and bearings.
Why Does Engine Oil Change Colour Over Time?
Engine oil changes colour because it:
- Absorbs carbon deposits from combustion
- Traps dirt, soot, and microscopic metal particles
- Is exposed to high temperatures
- Circulates through moving engine parts
Darkening oil is normal and shows that the oil is cleaning and protecting your engine. However, certain colours or textures can indicate serious faults.
Engine Oil Colour Meanings Explained
Amber or Light Brown Oil
✅ Healthy oil
- Indicates fresh or lightly used oil
- Smooth texture and clear appearance
- No action required
This is exactly what you want to see during routine oil checks.
Dark Brown Engine Oil
⚠️ Normal for used oil
- Common after several thousand miles
- Especially normal in turbocharged engines
- Safe if oil feels smooth and thin
Check your service history to see if an oil change is due soon.
Black Engine Oil
⚠️ Usually normal, especially in diesel cars
Black oil does not automatically mean your oil is bad. Diesel engines, in particular, darken oil quickly due to soot buildup.
However, black oil should be changed if it:
- Feels thick or gritty
- Smells burnt
- Has exceeded the service interval
Thick, Sludgy Black Oil
🚨 Oil has failed
- Poor lubrication
- Increased engine wear
- Risk of oil starvation
Change the oil immediately to avoid engine damage.
Milky or Cream-Coloured Engine Oil
🚨 Severe engine fault
Milky oil usually means coolant has mixed with engine oil, often caused by:
- Blown head gasket
- Cracked cylinder head
- Failed oil cooler
Stop driving immediately and book a garage inspection.
Grey or Metallic Engine Oil
🚨 Internal engine wear
- Presence of metal particles
- Bearing or piston damage
- Oil no longer protecting the engine
This is a serious issue that requires urgent diagnosis.
Foamy or Bubbly Engine Oil
⚠️ Oil aeration or contamination
Causes include:
- Overfilled oil
- Air trapped in oil system
- Coolant contamination
Foamy oil reduces lubrication and should not be ignored.
Green or Yellow-Tinted Oil
⚠️ Antifreeze contamination
If your oil looks greenish or yellow:
- Coolant may be leaking into the oil system
- Gasket failure is likely
This can lead to catastrophic engine damage if left unchecked.
Can Engine Oil Be Too Dark?
Yes. While dark oil can still be effective, engine oil that is excessively dark, thick, and gritty has lost its ability to lubricate properly.
Signs oil is too old:
- Sticky texture
- Sludge on the dipstick
- Strong burnt smell
Ignoring old oil accelerates engine wear and reduces fuel efficiency.
How to Check Engine Oil Colour Correctly
- Park on level ground
- Switch off the engine and let it cool
- Remove the dipstick and wipe it clean
- Reinsert fully
- Remove again and inspect the oil colour and texture
Check your oil at least once a month and before long journeys.
Does Dark Oil Always Mean I Need an Oil Change?
No — oil colour alone isn’t enough.
You should change your engine oil if:
- You’ve exceeded recommended service intervals
- The oil is thick or gritty
- The oil smells burnt
- The engine sounds noisy or rough
Always combine colour checks with mileage and service history.
How Often Should Engine Oil Be Changed in the UK?
Typical UK oil change intervals:
- 6,000–10,000 miles (older petrol cars)
- 10,000–18,000 miles (modern petrol and diesel cars)
- Every 12 months, even with low mileage
Short journeys, cold weather, and stop-start driving may require more frequent changes.
Does Engine Oil Colour Affect Performance?
Yes. Poor-quality or degraded oil can cause:
- Reduced fuel economy
- Increased engine noise
- Sluggish acceleration
- Excessive engine wear
Clean oil ensures smoother running and longer engine life.
Final Verdict: What Colour Should Engine Oil Be?
✔️ Amber to dark brown – Normal
⚠️ Black and thick – Change soon
🚨 Milky, grey, foamy, or green – Stop driving and investigate immediately
Regular oil checks are one of the easiest ways to prevent expensive engine repairs.
FAQ – Engine Oil Colour Explained
What colour should engine oil be on the dipstick?
Engine oil should be amber or light brown when new and gradually darken with use.
Is black engine oil bad?
Not always. Black oil can still protect your engine, but thick, gritty black oil needs changing.
Why is my engine oil milky?
Milky oil usually means coolant has mixed with the oil, often due to a blown head gasket.
Can I drive with dark engine oil?
Yes, if it’s still smooth and within service intervals — but change it if overdue.
Does diesel engine oil turn black faster?
Yes. Diesel engines produce more soot, which causes oil to darken much faster than petrol engines.
