OK. So I've just taken the trusty Beachy for a serious belt around the lanes touching 70+ here and there, a distance of about 60 miles. On the last couple of miles I noticed the low oil pressure light on at low revs, and on parking up, there's a definite oil drip from underneath, although the top of the engine seems dry and dusty. Checked oil level and the oil's clear and not dirty, but appears to have an unusually low viscosity. The level is also *over* the "max" line on the dipstick.

My question is:

Can the fuel pump diaphragm rupture and cause petrol to get into the crankcase, thus diluting the oil and raising the level in the sump? I know it can on a DS, but given the superior engineering is this possible on the 2CV too? Am I in line for a crankcase explosion??!

The 'dry' side of the diaphragm is vented to atmosphere and the centre of that fibre pump spacer should have been packed with grease on installation as a second line of defence.

How much above the 'max' level is the oil level?
If the oil level is way over the 'max' mark, the camwheel will dip into the oil, resulting in frothing and possible overheating.

Maybe also worth checking that the oil pressure switch isn't on the way out.
They seem to weep for a while, so that the oil pressure warning light flickers, before letting go properly...

ken

OK, but if pump is old or not greased can fuel get into the sump? Oil level is about 6-7mm above the "max" line. It was on the line when the oil was last changed, about 300 miles ago.

On second thoughts,
I probably tackled this back to front, since the immediate result of a punctured/split diaphragm would be a lack of fuel being delivered to the carb.
If the leak was very small, you should still notice fuel leaking from the vent hole(s) at the back of the pump when the engine was ticking over.

Also, if the engine is reaching its proper operating temperature, wouldn't any petrol be 'boiled' off, in the same way as water vapour from blowby is dispelled through the breather?

ken