What is this peanut butter substance?

I was changing my oil today when I took off the filler cap and it looked like there was creamy not crunchy peanut butter on the inside of the cap and a little down the neck. A little background about the truck.
2005 4.0L 88,200 miles and always use Mobil 1 5W30 with toyota oil filter.

 

moisture buildup

 

I get that junk on my truck sometimes too.

 

looks like moisture to me,you drive alot of short trips??

 

x2...The "Sludge" is caused from shorts trips...your engine doesn't heat up enough to burn off the excess moisture...and this is what you get. Just clean it out the best you can and change your oil a little sooner in the cooler months of the year

 

http://www.tacomaworld.com/forum/2nd-gen-tacomas/148371-whats-mustard-colored-substance.html

 

This happens all the time to my truck in wintertime.
Summer time it clears up.
Same as you, Mobil 1 & toy filter. Been doing this since it was new. Now 55k.

 

Yea that would make since. Most of my trips consist of 5 to 10 minutes. Thanks for the quick reply guys.