I have a circulating tank heater and wonder if it is the right size for my240d. The cooling system is 12 quarts and the heater is 850 watts. Thanks.

 

An 850-watt circulating tank heater is generally adequate for a 12-quart cooling system like your 240D. It should be able to warm the coolant effectively without overloading the heater. Keep in mind that heating time depends on ambient temperature, but for typical cold-start preheating, this wattage is sufficient. Always make sure the heater is fully submerged in coolant while operating and never run it dry.