I have found a relevant quote from here that might be related:

Plugged-in engines are already half-warmed when started. Fuel consumption is thus reduced by an average of 15 per cent over the first 20 kilometers driven (after which, the engine will be fully warm) according to the CAA.

I know also that all fluids become more viscous as temperature decreases, and so the engine oil becomes thicker and requires more fuel to pump it around when it is cold. The battery also experiences a higher strain due to the increased current draw from the starter motor when the driver tries to start the car in the cold (they perform a cold start).

What is meant if an engine is "plugged in"?

Note: This question applies to non-electric cars.

1 Answer 1


In very cold climates there are electric heaters that replace the dip stick. They are plugged into an AC outlet and because they reach the oil pan they can apply heat directly to the oil. That way the oil doesn't get cold to the point where it totally looses it's ability to keep your engine protected at start up. It's plugging in that electric heater that "plugging-in" refers to. In places like North Dakota parking lots have electric outlets for each spot just for this.

Hope that helps!

  • Never knew they replaced the dipstick. Is that the way they all work?
    – JPhi1618
    Jan 25, 2016 at 21:07
  • 1
    If you search for engine heaters you'll find both dip stick and whole block heaters. A block heater is better because then all of the oil, not just what's in the sump get's heated. Main thing is "plugged-in" refers to connecting either a dip stick or block heater to an AC outlet to prevent the oil from being to cold to work when you start your car.
    – cdunn
    Jan 25, 2016 at 21:11
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    Heaters come in many different flavors. There are blankets that are glued to the bottom of the oil pan. Some engines have special places that allow screwing in a heater. Some cars have a special freeze plug that is heated. Some vehicles have an adapter in the oil filter housing that has a heater. Further there are battery heater blankets and battery trickle chargers that may also be installed.
    – vini_i
    Jan 25, 2016 at 22:06
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    There are also heaters which are placed inline with one of the two rubber hoses which supply coolant (heated coolant) to your heater core. This is the type I was most familiar with as a kid growing up in Montana. Jan 25, 2016 at 22:08

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