The oil cooler sits in the V valley between the cylinder banks, under the intake manifold, where the oil circuit and the coolant circuit meet. Its seal ages, and from then on it leaks along two paths. Outwards the oil collects in the V valley, runs down and leaves traces on top of the engine and around the intake manifold, so for a long time all that shows of it is that the oil level falls. Inwards the two fluids mix into each other.

The signs of the mixing are clearly visible. A mayonnaise-like, frothy deposit appears on the oil filler cap and on the dipstick, an oily film settles in the expansion tank, and the coolant level falls with no external leak. White smoke from the exhaust can come with it, overheating without any visible loss of fluid, and uneven running.

Once the seal has started, the leak accelerates. A few weeks of inattention is the difference between a seal replacement and a rebuild with connecting rod bearings, because oil diluted with coolant does not lubricate the bearing.

The repair costs between 1700 and 3800 euros and is a one to two day job: the cooler can only be reached after the intake manifold has been removed and the engine partly disassembled. The labour makes up the price, not the part.