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Checking for oil leaks

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If an engine needs topping up with fresh oil more than usual, or if you see a pool of oil under the engine where the car has stood, there is an oil leak. Trace the source immediately.

Look carefully for leaks down the back, between the engine and the bulkhead - use a mirror if necessary.

The engine could be damaged if the leak is allowed to become serious.

Finding the exact source of the leak is easier if you first clean the outside of the engine thoroughly with a proprietary degreasing fluid and a stiff bristle brush . Protect electrical parts with plastic bags, or plastic sheets held on by sticky tape, then hose the degreaser away with water until the engine is reasonably clean and oil-free. Leaking oil then shows clearly.

Timing-cover oil seal

The pulley wheel will spray oil from a leaking timing-cover seal.

A common source of leakage is the timing-cover oil seal at the crankshaft-pulley end of the engine. Generally, oil leaks most from the seal when the engine is running fast, less when it is idling.

Check for signs of oil sprayed out sideways in line with the oil seal or pulley on to adjacent parts of the bodywork or engine.

Look also at the underside of the engine beneath the seal, and on the sump pan for oil streaks starting at the lower edge of the seal.

The only cure for a leaking oil seal is replacement, and ensuring that the rotating parts with which it is in contact are smooth and free of burrs or raised metal.

Checking a crankcase side-cover gasket

Tighten the central bolt sufficiently to compress the gasket.

On some engines — such as those fitted to certain Leyland cars — there is a cover over the camshaft tappet chamber on the side of the crankcase about halfway down the engine.

The cover is hidden by the inlet or exhaust manifold , so leaks from its gasket may be hard to spot.

With the engine running, look for oil coming from the lower edge of the cover. You may need a small mirror and a torch to see.

Tightening the cover securing screws slightly may cure the leak. If not, replace the gasket (See Replacing gaskets and oil seals ).

Looking for leaks on the crankshaft rear oil seal

Oil under the clutch housing may come from the crankshaft seal.

The crankshaft rear oil seal is usually hidden by the flywheel and clutch housing, so the only visible sign of a leak is a drip from the bottom of the clutch housing . Where the seal is leaking badly, there may be clutch judder or slip caused by oil spraying on the clutch.

Replacing the seal is the only cure. This means removing either the gearbox or the engine — a job best left to a garage.