Bob's Mechanical Repairs

Engine oil leak — MOT advisory and failure explained

Bob's Mechanical Repairs — independent family-run garage in Birnam, Dunkeld, Perthshire. Call 01350 727 276 or email [email protected].

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Oil is escaping from the engine. A weep or a light film is normally an advisory. It becomes a failure when the leak is dripping so badly it could reach the road or a hot component, or where it has contaminated something safety-related like a brake or a suspension bush.

Wording as it commonly appears on an MOT certificate: “Engine has an oil leak”.

What does it mean?

Oil is escaping from the engine. A weep or a light film is normally an advisory. It becomes a failure when the leak is dripping so badly it could reach the road or a hot component, or where it has contaminated something safety-related like a brake or a suspension bush.

How serious is it?

Usually recorded as: Advisory, Major. The tester assesses the actual vehicle on the day, so your certificate is what counts.

What normally causes it?

  • A rocker or cam cover gasket — the most common and the easiest to fix
  • The crankshaft front or rear oil seal, the rear one usually meaning gearbox-out labour
  • A sump gasket or a stripped sump plug thread
  • A blocked crankcase breather building pressure and pushing oil past good seals
  • Oil filter housing seals, which are a known weak point on several common diesels

What a mechanic would check

Degrease it, drive it, then look with a UV light or fresh eyes — oil always tracks downwards and backwards, so the drip point is almost never the source. I also check the breather system before condemning a seal, because replacing seals on an engine with crankcase pressure just moves the leak somewhere else.

What might need replacing

  • A cover gasket or seal
  • A sump gasket or a repair insert for the plug thread
  • A breather or PCV valve
  • Crank seals in the more serious cases

Can you still drive it?

A weep is a watch-the-dipstick job. Check the level weekly and top up with the right grade. If oil is landing on the exhaust — you'll smell it and see smoke off the bonnet — get it fixed before it becomes a fire risk.

More other mot items failures · MOT failure decoder · Ask a mechanic about your certificate

This is general guidance from a UK mechanic, not a substitute for a physical inspection. Only the tester who inspected your vehicle can confirm what was recorded and why.

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