The other day I was adding some oil to my 2002 Impala LS and when I looked under the oil cap I saw a creamy mustard colored type residue under the cap. Does anyone know what that may mean?

 

a lot of engine's with a few miles on them that do not get driven enough to fully warm up seam to get a build up there and the valve covers .the moisture in the crankcase is not getting purged out with the blow buy gasses it's a natural thing with age ,do you do a lot of city driving and short hop's ?do you change the oil on a regular scedule to help keep it clean inside

 

Yes. It's moisture build up from the oil not getting hot enough to evaporate the moisture due to short trips and colder weather. Nothing wrong.