Pablo's right.The pellets contain wax,as a lubricant,(hence the name wax pellets)and they contain a filler,similar to Barrsleaks,which will help fill pin holes in the radiator and heater core.But while we're on heater core,it is also a very likely source of sludge.If the heater isn't used frequently,even in summer,then sludge will build up in it and the first time you run the heater it will release the sludge into the rest of the cooling system so make sure that when you flush your system that you have the heater on so that it too can be flushed.Again,as Pablo said,the wax from the pellets feels like just that-,wax not engine oil.Good luck