Webasto Thermo Top EVO Diesel Coolant Heater Kit 12V w/ SmarTemp (5013379A)Webasto Thermo Top EVO Diesel Coolant Heater Kit 12V w SmarTemp (5013379A) From trucks to buses to off highway equipment, the Thermo Top EVO is the most widely used coolant heater with over a million at work. 17,000 Btu h of heat will bring the engine up to operating temperature so it's running efficiently. That means you save fuel, reduce engine wear, maintenance costs and exhaust emissions by not idling.