How to Run a Block Heater Without an Electrical Outlet


A cold automobile engine has a harder time starting in the deep freeze of midwinter than any other time of the year. If the ambient temperature is too cold relative to the battery's effective capacity, the car just might not start at all. Block heaters are devices that combat such circumstances by keeping a portion of the engine warm, enabling it to start much more easily. Some block heaters operate on 120v electrical power; but when the car is, say, in an airport parking lot overnight, you won't have access to a standard wall outlet.

To improvise a block heater that works anywhere, plug the block heater into a 12v power inverter. But don't hook the inverter up to your car battery, as this may drain it beyond its ability to start the car.

Things You'll Need

  • 12v car battery
  • 12v-to-120v power inverter with direct-to-battery cable
  • Electric timer
  • 12v battery recharger
  • Crate, box or straps
  • Secure the battery in your car trunk where you have easy access to it and it won't tip over. You can place it in a small plastic milk crate or a cardboard box, for instance, or strap it with elastic hook straps.

  • Place the battery cables on the battery terminals, black to black and red to red, and hook the other end of the cable into the power inverter. Turn the inverter on and plug the block heater into it as you would a standard outlet. Run the cable from the trunk to the car engine.

  • Place the block heater on the car engine as directed by the instructions. Some heaters replace the dipstick while others are laid across the block or oil pan.

  • Remove the block heater and turn off the inverter before starting your car. When you reach a place that provides access to electricity, recharge the battery so you have full power for the next time you need it.

Tips & Warnings

  • The Hamilton County Air Quality Management Division recommends turning on a block heater two hours before you plan to start the car in frigid weather. If you desire to do this, plug an electric timer into the inverter first, then plug the block heater into the timer.

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