Engine block heater - how long does it take to warm up?

How long do you need to plug in your engine block heater before you can unplug, start your car, and be on your way?

To save energy and money this winter, I plan to put mine on an automatic timer but I need to know how long to set it for.

Is 20 minutes enough?

It depends on the ambient temperature. If it’s only 32 degrees outside, it may take an hour. If it’s -32 degrees it could take four hours. So figure anywhere between 2-3 hours on average.


How many watts is the heater rated for?? A 1200 watt heater will do the job in an hour or a little less…

The block heater will reach the best (optimal) temperature in about 1 1/2 hours. If it is very cold, it will warm the engine block just warm to the touch. If it is 32F, the engine will feel a lot warmer. In any case the timer need not be on longer than 1 1/2 hours. I have used timers for 40 years, and have worn out 4 of them. Block heaters have dual benefits; they allow easy starting with reduced engine, battery and starter wear, and in addition they save gas. The little bit of electricity used has a big payoff. For some people, getting heat in the car quickly is also a major benefit.

It depends on the temp, kind of car/engine and how big a heater you have. If you have a temp gauge you can figure it out by yourself if you can keep a notebook.

If your primary purpose of having a block heater is to have instant heat, it’ll take a while with a traditional magnetic one or freeze-plug one. The kind that install in the coolant stream and have a little pump to circulate the coolant around work great-- you don’t even need to start the engine to get sort of lukewarm air coming out of the heater core.

If you want to get into a warm car, buy an in-car electric warmer. They install under the dash or on the passenger side kick panel. They are about 300-400 watts, and can also be put on the timer with the block heater. The block heater’s function is not to warm the car interior; it just makes it warm up quicker because the engine water jacket is already warm. The aditional benefit of an interior warmer is that it keeps the windows clear since the warm air is circulated by the fan.

I find that mine (about 450W) takes 2-3 hours to reach maximum temperature (about 40C). If it’s really cold, I normally just leave it on all night because it really uses very little energy:

450W * 6 hrs = 2.7 kW-hrs (maybe $.40).

Good return on investment! Right now it is -4F but the temperature in my garage is 24F, so 1 1/2 hours is plenty. If the car is parked outside with a breeze blowing, it might make sense to just leave it on. The very long life of your cars is no doubt partly due to the absence of really cold starts, which each amount to the equivalent of 500 miles of engine wear.

A block heater does save some wear and tear on the engine and starter. It’s also nice to have cabin heat right away. I usually don’t use mine unless it’s expected to be really cold overnight (below about 15F). Some folks do have a heavy duty timer installed in their garage to turn the heater on a couple of hours before they need the car.

you can just plug it in when the temp is going to be below say… 40, but DONT forget to unplug BEFORE you drive away.

driving away with out unplugging it will quickly negate any benefit (both cost and performance) of having a block heater!

most of them have a built in thermostat so they dont overheat the block. (as opposed to wasting electricity needlessly)

what is the best way to heat an engine? i have always thought that a coolant heater is the best way to do vs dipstick heaters.

In Alaska some people use a dipstick heater in addition to the water jacket coolant heater. The dipstick heater only warms the oil, which is Ok for the oil, but the engine will still need a long time to warm up.

Some companies stopped making the dipstick heaters because there have been reports of the heater starting fires in the engine.

Agree; you have to pick the right wattage, and the oil could overheat, since there is only a small amount of fluid to warm up. I don’t normally recommend dipstick or stick-on magnetic crankcase heaters for those reasons.