I repaired my cooling system hose and I decided at 65K miles it was time to do a full flush. I dumped all the coolant and used a flushing agent (Royal Flush). I dumped the flushing agent and filled with pure distilled water. I flushed that. I'm now on my 2nd 100% pure water flush. I am noticing this black particulate matter that keeps showing up in my expansion tank. It looks like flakes but I'm sure if you look inside of yours you will see tiny black dots. Anyone know what this is and if this is the sign of anything failing? I used a turkey baster to remove it. It appears the expansion tank design is somewhat designed to handle this as it has several compartments and the first compartment is for sediment.

I'm just wondering what is this sediment. I was hoping it would disappear by the time I got to pure water on the 3rd flush. It is not like a teaspoon of anything mind you. Just a few small specs.

 

Strange stuff. If you put some of the black stuff between your fingers and press them together it just completely presses into nothing. I read someone said it can be mold or the interior of the rubber hoses breaking down over time. It seems to be common. It might be even a function of flushing out the crap. https://forum.miata.net/vb/archive/i...p/t-65745.html

 

Do you have a picture? I would be interested to know what it is as well. I would assume - not having read the attached post - that mold would have a difficult time growing in a neutral to basic pH environment with relatively low oxygen combined with high heat as found in the cooling system. However, if the car is driven rarely and the fluid is allowed to become more acidic, with access to O2, mold could grow - or bacteria for that matter... yeast too... radiator beer anyone?

Anyway, I think it is rubber particulate from inside the hoses which are breaking down as mandated by the EPA after 2004 for all rubber used in cars to be biodegradable. We all be having fun with this legislation for decades to come

 

I was going to take a picture but all you would see are black specs. Yes, I believe it is the rubber inside of the hoses. If you squeeze it, sort of has a spongy, rubber look to it but if you keep squeezing it, it basically turns into just a black liquid.

I'm not sure what moron at EPA thought that rubber hoses in a car should break down but it doesn't surprise me.

So, this sounds like another good reason that when it is time to replace my thermostat, and water pump, I will put in all new Silicon hoses from China outside of the US EPA guidelines that will out live the nuclear holocaust, and as such, the EPA as well since that is the first major US city to go in the upcoming WW3.

 

I bought a used MCS recently that had gray-black crud in the cooling system - I think it is remnants of leak sealant additive. It was plugging up all the coolant passages in the block, the water pump, the crossover pipe, etc. Perhaps you are seeing the remnants of something like that put in by a previous owner?

 

I am pretty sure it is rubber from the hoses.

 

What is the source of this item?