Oil dilution is a real thing. An operational reality. It’s more of a factor now than ever before. Here’s the background briefing on that.

Especially in a cold engine running rich, fuel can condense on the cylinder walls, where it sort of dissolves into the thin film of lubricating oil that’s there. The oil, only a few microns thick, is trying to maintain a death grip on the fine scuff marks honed into the bore. And the fuel’s not helping.

Here's what Wikipedia says about crankcase dilution >>

When the rings sweep past, downwards, they scrape it off. The oil, diluted with fuel, is flung into the crankcase. This is happening about 8 times a second for every 1000rpm - per cylinder - so you don’t need all that much fuel per combustion event to get mixed up in this way, for it to really add up over time. And the result is: Rather a lot of fuel can end up mixed with the oil. More detail on the phenomenon in this report on oil dilution >> from Total.

It’s not good - not desirable, anyway - but it is known about, and it is taken into account in R&D at both oil companies and carmakers - we’ll get to that.

Basically, fuel, petrol (gasoline) is to lubrication what Idi Amin was to humanitarianism. The function of oil is to maintain a tough, thin, slippery film between the critical metal interfaces in your engine - on the bores, in the bearings, the cam lobes and valve guides, the timing chain - all the expensive stuff that moves really, really fast, with great precision.

Metal-on-metal contact is the enemy of longevity, and oil is the cure. Fuel in the oil degrades the effectiveness of the oil.

Get a great price on engine oil at Sparesbox >>