Likely previously scraped off or incompletely applied. After 25 years and 470,000 miles I have not seen mine erode in any way.
Carbon deposit on "baffle" under engine oil fill cap - used 2015 Toyota Highlander
- Thread starter NissanMaxima
- Start date
2005 likely called for 5W30. "Hybrid oil" would have been synthetic blend which is code word for very good conventional. As long as 5K oil changes were done it should be fine.
'18 HYUNDAI Accent w/ 1.6 Ltr. ( G.D.I. ) baffle . Could the buildup be from bad P.C.V. or just normal ? Nasty looking , but looks to be good inside the engine like others previous pictures . Any other out there have the baffle , if so post picture(s) . 
Around 20 minutes after 24 mile drive .
About 24 hours after drive .
Around 20 minutes after 24 mile drive .
About 24 hours after drive .
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I wouldn’t be afraid of it if everything else is in good shape. You know the oil was changed regularly. Even if it was cheap bulk it was changed every 5k so….
You could run some Rislone or HP cleaner through it for a while for good measure.
The coating on the baffle is not from the oil. Here is the baffle on my engine. It has looked exactly like this more or less for 25 years and 470,000 miles.
If it’s not from the oil what is it from?
It was applied at the factory, they were all like that. Why I do not know.
At the time some people speculated it was for vibration control but I don’t see how that could really be the case.
Thanks for the explanation! Seems to bubble.
Thanks everyone. Mine has a non-uniform appearance - some areas clean metal, and others the baked on oil look. That's why I thought it was baked on oil. Now that I bought the car, I can take a better photo and post it tomorrow.