Scale on feed tube and injection lines.

[M249cummins]

While pulling the head I noticed this thick scale buildup on 2 feed tubes and 2 injection line ends. All on the outside none inside. Will flake off with hard scraping, what could cause this? It’s not rust FYI.

 

[Poulina]

Maybe algae from fuel? Has something to do with what’s in your fuel imo

 

[odieub]

Thats on the outside of the fuel. If was power washed could have got water in there?