Casting sand was bill’s tractor. mine is goo from sitting for 50 years. Was metallic mud. First time i ran it,no thermostat. It picked up crud and instantly plugged the rad. Im going to place some sort of filter in the heater hose in an attempt to collect some (if any) remaining junk. Thinking an oil filter will grab the junk,i have a remote filter mount. Just order a filter with no bypass.