Wow, I thought it was toxic waste all right . . . . I've only had the car for a few days. Doing a lot of maintenance on it, so I'll know where everything stands. some previous owner had already put the green to it, so I have the coolant system is cleaner than that tank was. But as tenacious as that DEXsludge is, what sort of coolant flush will touch it? It seems to be vulnerable to petroleum products, as that engine cleaner would go through it whereas strong alkali and detergent would not.