I just found some crud type stuff in my coolant overflow tank.... rx7 store rebuilt my motor for me about 2000-2300 miles ago. The crud is kinda like a muddy / lubricant type stuff. It is charcoal in color.

What this mean exactly? Is it normal left over stuff from a rebuilt motor?
Is it a sign that my brand new (2nd motor from the rx7 store) is going out already?

I'm going to flush the coolant system completely and use some redline water wetter with it, but I need to know what I am dealing with.

 

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/should-i-concerned-about-561321/

 

assembly lube gets mixed with the coolant and can clog things up....flush it out thoroughly

 

I appreciate the responses. Thank you!

 

I noticed the same thing on my AST cap. I've changed it since and so far no problems or gunk.

 

good to know with a new motor coming back soon!