Oil leak

I have an annoying oil leak from my 2001 Vauxhall Astra MKIV 1.8 petrol with the Z18XE engine and 115,000 miles on the clock. The leak developed on the timing belt side of the engine, which, with the plastic undercover removed, proceeded to blow out through the offside front wheel, covering the brake caliper in the process. This happened on a 24-mile journey and emptied up to one litre of oil – the dipstick was on ‘Max’ at the start of journey and halfway between ‘Max’ and ’Min’ at the end of the journey.

My initial thought was that the crankshaft oil seal had failed, as oil appeared to be coming from the lower area behind the rear timing cover, running down and round the sump, then dropping onto the exhaust, as well as being blown out through the wheel. The crankshaft and camshaft seals have now been replaced, as well as the oil pressure sender, and all seemed well while it was run up to temperature and 2500rpm on the driveway. But after a four-mile run, the area was once again dripping with oil, albeit slightly less than before. It appears to still be coming from behind the rear timing cover, slightly above the crankshaft and oil sender unit, and running down and round the rear of the sump onto the exhaust.

Suggestions have included checking the head gasket and oil pump/gasket. As a new timing belt kit was fitted when replacing the aforementioned seals, I am reluctant to remove them again to detach the rear timing cover (the retaining bolts are very tight and difficult to remove when fitting seals). A new cam cover gasket was fitted prior to replacing the seals and the front of the engine is dry. The car got a new head gasket three years and around 12,000 miles ago, after the cambelt snapped.

Do these engines have any known failure point that would result in an oil leak? The car has always run smoothly with plenty of power and continues to do so. Glen Redfern

For the oil to reach the brake caliper, it does sound as though it is coming out at force. If the crankshaft seal was leaking, I would expect to find the oil soaking the cambelt area and cover. The oil pressure switch would be a likely source for the type of leak you have, but as you have already replaced that, this can be eliminated.

The oil filter housing is at the other end of the engine block, so the most likely reason for your unwanted oil leak is the oil pump housing-to-block gasket. I do appreciate that replacing this will mean repeating work you have already carried out, but it is the only remaining possible source of the leak.

I do remember a problem with the oil pump-to-block gaskets which did affect the diesel engine version, so the gasket was changed from paper to steel because of its tendency to fail. This may also apply to the petrol version.