I noticed this as well while changing my oil yesterday, glad to hear its normal. My coolant was a nice red with about 2" of black at the bottom. The sludge drew my attention to the reservoir and i noticed its at the MIN level with 40 000 Km on it? Is this normal, and do i just top it off with coolant from the dealer? Thanks for the Help!!

 

I have it in my 89 and it has no effect on anything. Don't have it in my 10 I guess it's too new. Thanks Tinman.

 

Finally I have an answer for this! I'v been worried about it, but didn't have the time to go to the dealer.