Does anyone know what this stuff is that is floating around in my coolant reservoir?

 

Is that same stuff floating around under the rad cap too?

 

It was too hot to open. I'll take a look at lunch.

 

That's what I'd be more concerned with. My overflow bottle is a little dirty on the inside as well but the coolant that actually flows through the cooling system is what really matters

 

They look like little bits of rust particles.

 

I'd say rust doesnt float....like 1996 said have a look at the radiator cap. Oil floats, is more concerning. When in doubt, flush system and check again.

 

maybe some kind of stop-leak

 

Nothing showing in the radiator.

Just did a complete radiator, block, reservoir, and heater core flush a month ago and replaced the thermostat. It wasn't really dirty before the flush, just doing routine maintenance to establish a base line since I bought it last winter.
Since the flush I have been losing a little coolant. I replaced the radiator cap and found my lower hose was leaking at the radiator. Thought I had it but still losing a little somewhere. I pulled the lower splash shield and fan shroud and idled it with the AC on, up to temp, looking for a drip anywhere. Smelled of hot coolant over the engine bay but nothing wet. I accidentally let the reservoir get low but filled it before the run up. When it got nice and hot it burped a little into the reservoir and came up with the floaties.

The head was replaced with aftermarket before I got it. Casting mark on the head is "DD" - 66,000 miles on it now. It runs cool, rarely gets over the 210 mark.

 

It looks like old line debris probably knocked off when you were re-doing everything. If your radiator is clear then I wouldn't worry too much about it. Maybe just keep an eye on it and see if the debris amount increases.

It's a shame there isn't a radiator filter that could be installed somewhere in the cooling system that one could regularly change out like an oil filter. Or even one that you could put in temporarily when doing a system flush. But I don't thing there is enough water pressure to allow for the blockage a filter would create.

 

Oh, I'm keeping and eye on it alright! I'm probably over-paranoid of the cracked-head syndrome. I even took an oil sample to send for analysis - back in 2 weeks.