A small amount of fuel in the oil is in fact normal. It really depends on how much.
"Symptoms of oil and fuel mixture beyond the normal amount
If you are unsure whether the mixture of gas and oil isn’t normal, here are a few symptoms and signs you can look for that can tell you whether there’s a problem with the car or not.
- You can smell a strong odour of fuel as you are driving the car
- Your car emits an opaque white smoke from the exhaust rather than a clear smoke
- Your dipstick shows that your oil is either overflowing or the level is increasing without actually adding any oil
- Your dipstick smells more like gasoline than oil
- The oil on your dipstick drops off like water droplets
- The oil pressure gauge shows low oil pressure
- You notice that, while changing the engine oil, the oil seems not so viscous
If you encounter any of these symptoms, it may be that there’s an excessive amount of gas getting into the oil in your engine which isn’t normal. A rather easy way to tell if your car is using too much fuel is that your car will emit thick white smoke.
That is due to the fact that fuel that is not burnt properly during the combustion cycle will tend to ignite later when on its way out of the cylinder. Also, since oil is viscous and gasoline is not, if you realize that your engine’s oil is thinner than it should be, even after a long time of use, there’s a high chance that it’s the gasoline that is changing the viscous properties of the oil."