Inquiring minds want to know so I asked a GM engineer whose speciality is engine cooling. I sort of view what he says as the voice from Olympus. He sees it as OK to do. Here is his reply:


Honestly I do not know the answer to your questions. I would not expect the silicates to be doing anything harmful to the engines...based on the fact that they seem to run OK after doing this to them I assume this is kind of a moot point. I don't know what in the additive package would have a cleaning effect like you observe. I suspect the ethylene-glycol is dissolving the crud and it just becomes saturated with whatever compound the crud is made of and then it will not "clean" anymore....Kind of like trying to clean salt off of something with saturated salt water...it would not dissolve anymore salt but would not necessarily be "worn out". I think that the fresh ethylene-glycol just dissolves more stuff. The family of glycols can be fairly aggressive solvents ... brake fluid is a glycol and you know what it does to some paints. Maybe fresh brake fluid would be a good substitute cleaner. Or, you could try the same experiment with DexCool and see if it cleans the same. If it did then it obviously wouldn't be the silicates as there are none in DexCool and it is still an ethylene-glycol coolant.