Shell Rotella ELC Extender is a patented inhibitor, providing complete cooling system component protection, also help reduce water pump failures, hard water scale deposits, silicate ?green goo? and improve heat transfer. Tests with ROTELLA ELC show that heat transfer is about 8% better with RELC than with conventional heavy duty, silicate-containing coolants. The inhibitors in ROTELLA ELC, due to their special chemistry, are designed to go 600,000 miles on-road or 12,000 hours off-road with only one Shell Rotella ELC Extender addition at 300,000 miles or 6,000 hours. After 600,000 miles or 12,000 hours it is recommended that the coolant be tested for continued use.