97 expedition

was wondering once agian if anyone had any idea,s on why my oil cap seems to be geting a lot of white milkey color on there .in the past i had asked and some thought it might have been condensation but im not to sure know. as there was a lot on there the last time i checked. once agian i checked the oil and none on the dipstick my engine temp has not changed nor have i ever over heated.any help would be so helpfull .is there a pcv valve or soem i meet need to change to get this to stop before it does magor damage