Whats that foamy stuff under the oil fill cap & inside the filler tube?
If you look closely, you probably also see water droplets mixed in or nearby the foam. If you find either, there is probably nothing you can do to permanently get rid of them. Luckily, you don’t need to. A change in your driving pattern to include more driving under high load and fully warmed, and less driving of short trips or while the engine is cold, might do the job. Enough of such a change will do the job if your car is totally stock. What you see is an emulsion, oil mixed with water. Your oil includes emulsifiers as part of the additive package. They cause water to actually mix into and “disappear” within the oil. To a point, they do exactly that, preventing small amounts of water from congregating in any one place that might result in oil starvation in a critical location. As long as the amount of water doesn’t exceed the ability to the emulsifiers to disperse them, no harm is done. All engines are subject to condensation from the normal heat up and cool down processes, the same
