If its milky, thats coolant in the oil.
If its thin (and thats a very subjective measurement) you probably has some amount of fuel dilution, but in most cases if you can tell its effect on the oil visually then its WAY past the danger point.
Lastly, different motor oils react differently from engine to engine, even engines of the same type, configuration and so on. You could take L67 engine #100 and L67 engine #101 directly off the assembly line and put the same identical oil in them and drive the cars in identical fashions and in identical conditions and they will wear and react in completely different ways. The only real way to tell how well or how bad a motor oil is holding up in an engine is with oil analysis. Anything other than that is speculation at best.
