No heat

It works now, great. Unfortunately the black foam rubber is consistent with one or more coolant hoses shedding material from the inside. When the car has been off for a while feel along all the hoses and see if there are any mushy spots. If there are, change that hose. If more black chunks show up maybe change the lot of them? The car doesn't have anything in the coolant loop analogous to an oil filter, so any rubber that breaks off can go round and round until it finds its way into a place where it sticks and then causes problems.

 

I'm having a sense of déjà vu. I think there were some older threads, like several years ago, involving mysterious black foamy bits getting flushed out. Don't know what kind of search might be needed to find those threads again.

Black rubbery chunks might be suggestive of hose degradation, but the black foamy chunks seemed to puzzle people more. I'm not sure there was ever a satisfying explanation in those earlier threads either, but I'm not sure how well I remember. As I said, I think it was several years ago.

 

It doesn't seem like too much of a stretch (ha ha) that rubber from the hose could change configuration some when bouncing off the hot walls of the motor and passing through water pumps. The real test would be to do a chemical analysis of the foamy ones (after washing them thoroughly with distilled water) to see if they are the same chemical as the stock hoses.