Yellow gunk on oil filler neck
 

I just pulled the cap off the oil filler neck to add oil to my '02 996 and found yellow gunk on the inside of the cap and top of the filler neck. Any ideas what this is?

You could search this topic. We have seen this before. I recollect the majority opinion is that this is moisture and oil additive residue that collects on the filler and cap in very cold weather. I saw it on my 2000 Carrera, wiped it clean, and never saw it again in 3 years.

It's common, especially in the cold weather. The prevailing thought is not going easy on it will help prevent the formation of that crap.

emulsification of oil and condensate at the highest point in the engine. Typical in cold weather with short trips. Nothing to worry about, but take it for a longer drive every once in a while to burn off any water.

Thanks for the help with this--going out now to take your advice!

Take longer trips!

Search it, happens frequently. Cold weather and short trips. Prevent both and you'll never see it.

Can't stop driving it in the cold--too much fun--but will stretch out the drives. Thanks for the advice.

Get a new o-ring for the oil fill cap too. A better seal will reduce any chance of moisture getting sucked by and collecting into the fill tube there. Moisture is going to collect there regardless though.