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Experiment: how long should a block heater be plugged in?
Posted Thursday, April 17/08 in Mods & Tests
OK, so spring may not the best time to be talking about block heaters. Then again, the planet has two hemispheres, after all. So while it may be finally warming up here, somewhere somebody may be plugging in a block heater right now...
Plus, who says block heaters are only for sub-zero use? I use mine three seasons of the year. (And the only reason I don't use it regularly in the summer is because I'm lazy.) Toyota's hybrids (like the Prius) employ their thermos-like tanks to preserve coolant heat for efficiency gains whether January or July.
The question this post addresses is: how long should you plug in a block heater? In other words, what's the shortest time needed for the maximum temperature rise?
Why use a block heater?
I've written about block heaters before, so I won't go into much detail. From an efficiency standpoint, the big reason is because engines use less fuel when they're fully warmed up - as demonstrated in the cold start idling warm up experiment. In addition to efficiency benefits, they also decrease cold start engine wear and deliver heat to the cabin sooner.
Test details: two block heater styles tested...
The purpose of the test was simple: to measure the amount of time it takes to warm up the Firefly's 1.0L / 993cc engine from a cold soak (over night) condition with two different block heaters, separately and then combined. The block heaters in question are:
Both heaters use standard (North American) household power, 120 volts.
Temperature readings were taken from a ScanGauge every 15 minutes.
Note: the engine was started and idled for 30 seconds every 15 minutes to mix and circulate the coolant past the temperature sensor to get an accurate reading. This was necessary with the 800w inline heater due to "localized" (uneven) heating of the coolant. Both "pre" and "post" idling temperature readings are noted on the graph. The same method was used for the 300w heater measurements, even though there was negligible difference between the before/after idling temperatures with that heater.
300 watt warm-up time...
800 watt warm-up time...
1100 watt warm-up time (300w + 800w heaters running simultaneously)...
darin AT metrompg D-O-T com, or here