2006 Freightliner Coronado Coolant reservoir black

Does it look like black pepper flakes floating around?

even if it is compressor causing pressure in the coolant system it wouldn’t have the black flakes. The black is carbon in the coolant.


Take a pump up radiator tester and put on it. Do not pump it up. Start it and walk away see what kinda pressure you put on it in say 45 minutes or an hour. Anything over 9-10 lbs you got trouble

 

I can promise you it’s not the compressor. Compressor doesn’t have the combustion to cause those black flakes.

 

Old heater hose. Rubber breaks down and sheds. Did you lean on an upper or lower radiator hose during a service?

 

That is a sophisticated "bottle" test, I like it.. Its been so long ago, I don't exactly remember how to do it. But I do remember, in my case it was a very expensive test to fail. lol

I just did a refresher course on the bottle test "easy" I like @wore out method better