The correct way to check the engine oil level is to warm the oil up to proper operating temperature. Unless I have just changed the oil, I always check the level after driving several miles. Here is the extract from the owners manual which states the correct way of checking the level. Note that it states engine must be running – this is because the dipstick is housed in the disareator which in turn is positioned above the engine sump. Oil only fills the disareator when the engine is running – you simply wont get a reading when the engine is off.
Engine oil has a thermal expansion coefficient such that it can expand up to 10% in volume from cold to normal engine operating temperature. With a system capacity of 10 litres and a stated 1 litre capacity between the “max” and “min” marks on the dipstick, it is easy to see why overfilling is such a common mistake. If the level is taken when cold it will be at or even below the “min” mark – if the oil is topped up then an extra, unwanted, litre will be added.
This diagram shows how the oil circulates around the engine:
You can see that the disareator/separator is not only attached to pipes directing the oil flow but also the crank case ventilation system – it is this system that can cause issues (shown in yellow in the above diagram). Blow-by gases rich in hydrocarbons escape from the cylinders and into the crankcase, these gases are then diverted into the air intake to be burnt in the cylinders. The gases are taken from the crankcase and pumped into the top of the disareator to separate the gases from any oil before they are sent into the intake manifold.
If there is too much oil in the engine, the level in the disareator can be high enough to get into the pipe that sucks the gases into the air intake. If this happens lots of smoke will be pouring out of the exhausts as it is burnt up inside the engine. The smoke can damage the oxygen/lambda sensors and the oil itself can contaminate the MAF sensors and even get as far back as the air filters. Cleaning up after a overfill is a messy job – see this picture below of oil in the plenum chambers.
Ferrari recognised this as a problem and changed the disareator on later cars. Look at the parts diagram below for the two types – the newer part has a flatter top and the crankcase ventilation pipes are much higher up.