Home mechanic (basic tools) ยท Time: 10 to 15 min (estimate, during an oil change) (estimate)
Old oil tells a story about the inside of the engine. A few minutes of looking during an oil change can warn you about a failing bearing, a fuel or coolant leak, or a clutch that is wearing out. What you find is a clue, not proof. Confirm a fault with other checks before you open the engine.
Safety
- Wear nitrile gloves. Do not taste or sniff oil from close up for long.
- Hot oil burns. Let it cool in the tray before you put your fingers in it.
You need
- A clean glass jar, a strong magnet, a white paper towel and a torch.
Steps
- While the oil drains, catch some of the first oil in the clean jar.
- Hold the jar to the light. Note the colour: amber to brown is normal; black is old or very sooty; grey or milky means water or coolant.
- Smell it gently from a short distance. A sharp petrol smell means fuel is getting into the oil.
- Drip some oil onto the white paper towel. Look at the spot after a minute. Fine sparkle, grit or a dark ring of sludge are worth noting.
- Look closely at the strainer screen and the drain cap. On many engines the cap or plug has a magnet; look for a furry coat of metal on it.
- Run the magnet through the bottom of the tray. Steel particles stick; aluminium and bronze do not.
- Look at the size of what you find. Very fine grey paste is normal wear. Visible flakes, slivers, chips or pieces of rubber or plastic are not.
- Let the jar stand for an hour. Water sinks and forms a separate layer or droplets at the bottom.
- Write down what you found and the odometer reading. Compare at the next change.
What it can mean
| You find | Possible meaning | Go to |
|---|---|---|
| Milky or creamy oil, water drops | Water from short trips and condensation, or coolant leaking in | Oil is milky or creamy |
| Strong fuel smell, thin oil, level was high | Fuel getting past rings, flooding or leaking carburettor | Oil smells of petrol or the level rises |
| Steel flakes or chips on the magnet | Bearing, gear or cam chain wear | Metal particles or flakes in the oil |
| Shiny non-magnetic flakes | Aluminium or bronze wear (piston, bushes, thrust washers) | Metal particles or flakes in the oil |
| Brown fibre or grit | Clutch plate material | Clutch slips: revs rise but the bike does not pull |
| Black oil after a short time | Blow-by (gas past the rings) or overdue changes | Oil turns black very soon after a change |
| Pieces of plastic or rubber | Cam chain guide or tensioner wear on overhead cam (OHC) engines | Rattling noise from the cam chain area |
Check your work
- You kept a sample or a photo if you found something unusual. A workshop can use it.
- You cleaned the screen and magnet before refitting.
If it did not fix the problem
- This is a diagnosis step only. For chips, flakes or large debris, do not run the engine; see Assess bottom end and internal engine damage.