What is in this radiator?!?!?

It look and feels like black RTV. Could this be some form of stop leak? I changed the radiator and cap flushed cooling system and a week later I pulled the cap off and more of this stuff was stuck to the underside of the new radiator cap. Also the radiator in question is on my 2000 Camaro SS.

 

Looks like rust. Did you put antifreeze back in after the flush or just water?

 

Pre mixed antifreeze

 

wow that looks like shit. try just pull out the whole radiator n the main hoses n flush it all out. stick a hose in the rad when u pull it n flush it.

 

Looks like stop leak to me. Maybe some rust too.

 

I had this problem on my jeep. IMO, you probly have a air leak somewhere causing oxidation. I tightened some hoses, flushed the radiator and got a new cap and it solved the problem.

 

I ordered new upper and lower hoses and im going pull the coolant reservoir and flush it out. I'll double check all hose clamps and see if I can get a loaner cooling system pressure tester. What troubles me is it came back after flushing and installing a new radiator and cap after only a week. Other than that I dunno what else to do. Thanks for the input guys!

 

Electrolosis...?
Just throwing that out there. Happened in my bronco. Aluminum radiator + non dexcool + ground = crap similar to that.

 

Yeah, I think that's what mine was. Similar anyway

 

looks like antiseaze! prob a stop leak. ive never seen oxidation in the radiator but that looks super thick

 

Added to list of possibilities. I'm running dexcool antifreeze.

 

LOL if so I wouldnt be as mad I'd be more like hell yea my car makes free nutella!!

 

That could be the problem.

 

I thought so too but looking at my reservoir on my GMC Sonoma and inside the radiator it looks nothing like this and I havent changed the antifreeze since I bought it with 60,000 miles on it and I dont believe the previous owner did either and now it has almost 120,000. It has some brown sludge in it but nothing like in the pic. The stuff in the pic is black and rubbery like a silicone sealant. I can take pieces of it and stretch it.

 

I think he's saying Toyota recommends their own long-life coolant and not Dexcool which could be causing the problems. Honestly I've seen cars switched from orange to green to premixed prestone and haven't ever seen a problem. Only thing I have seen is dexcool gel up every so often when it's used in extended applications.

Like others have said a complete flush of the radiator. If it's solidifying though I have no idea, sounds like the making of trouble though.

 

Sorry I did not specify, the radiator is in my '00 Camaro SS.