Block heaters run 24 hours a day, 7 days a week, and periodically, they are going to fail. A block heater usually will not cause the engine not to run. A generator may need to be started up and allowed to run for a few minutes at no load so that the temperature comes up. This is not normally necessary, but will calm uncertainty over whether the generator will start cold or not. Low Coolant Temp Alarms are mainly the result of faulty block heaters.
Why have block heaters? A common misconception is that the engine does not need a block heater in California. A block heater does more than help the engine to start in cold weather. Due to the dissimilar metals that the engines are built with, accelerated wear can occur during start up. The pistons, normally made of aluminum, will expand at a faster rate than the iron cylinder liners. This rapid expansion of the pistons can lead to scuffing of the piston skirt. Block heaters relieve most of this scuffing by maintaining the cooling system temperature and keeping the cylinder liners expanded.
The extreme temperature inside the block heater is what causes the coolant to circulate through the system. (At times you can hear the coolant boiling inside of the block heater.) The block heater's high temperatures flash off the coolant into small amounts of steam, causing the coolant to evaporate in slight amounts. While it takes a long time to show a difference in the coolant level, recording the amount of coolant added to the system will help establish a trend. (The block heater thermostat is located at the cold side of the heater.) If the engine is continuously using coolant with no signs of leakage, oil samples should be taken and analyzed, and further troubleshooting should be done. If the block heater temperature gets excessively high, premature block heater failure or extreme engine damage may occur. You may notice that block heater hoses are cold in these systems. This is normal and is not a problem with the block heater.
Normal walk through inspections should include checking the cylinder head (or engine thermostat housing) for temperature and verifying that the engine or block heater hoses are warm. The temperature setting should be between 90 and 100 degrees, and never more than 120 degrees. The temperature gauge may read a different value than the thermostat setting. Some generators use a control panel to operate their block heater, particularly Onan's Power Command panel.