we all know that it's better to drive a cold engine gently than to let it idle after a cold start. it's generally accepted that driving uses less total fuel than idling to warm up first. driving also warms the motor up faster than idling (not to mention the drivetrain, tires, bearings, etc., which idling alone doesn't help.)
but how much faster? i didn't really know. time to get me some data!
i did a really basic experiment: i timed how long my car took to reach operating temp (195 F) idling, from a cold start.
(have some fun... before you read any further, take a guess at how many minutes it took, from 19 F ambient...)
<b>the test conditions:</b>
- ambient: -7 C / 19 F
- NO electrical accessories on
- cold soak (hadn't driven it since the day before)
- WAI in place
- didn't touch the accelerator at all - left the ECU to do its thing
note: a couple of minutes into the test i dope-slapped myself because i realized this was also a perfect opportunity to monitor changing fuel enrichment as the engine warmed up. so you'll see those figures start part way down the table - "liters per hour" of fuel consumption.
FWT: coolant (water) temp in degrees F
FIA: intake air temp in degrees F
Lph: fuel consumption in liters per hour
- it was shockingly slow to warm up, wasn't it. way off my guess. it only takes 3 or 4 minutes to reach operating temps when driven, though i'll have to wait until the ambient is the same and do a repeat test for a proper comparison.
- a larger engine might warm up quicker than my 993cc alumninum powerhouse, since it will be using more fuel (though it's also a larger heat sink...)
- since doing this, i have watched the Lph figure and have seen <b>2.0 Lph</b> (!!!) immediately after start-up. i'm curious to see how fast it tapers down to 0.8. the plot suggests Lph tapers faster in the beginning, which makes sense. it steps down relative to FWT at 110, 146, 172 F
The general public overwhelmingly believes in the "idle warm up", but as it's mentioned more that this is a bad idea, hopefully more folks will figure out that it's bad not only for the car, but for the environment. That's why I've decided to keep my engine block heater plugged-in all the time. I get to closed-loop almost immediately, and the overdrive kicks right in. Even after the car's parked for 5 hours, it's back down to cold start-up conditions, so the heater is needed even during the day. I'm sure it's sucking up some juice from the electrical grid, but the fuel savings has to even out the electrical use.
For older cars I'd recommend getting the inline block heater. Hell, I'd recommend it for newer cars too. Much easier to install and you don't have to remove the frost plug, which might come in handy one day.
MetroMPG, awesome data. Your experiments put me to shame.
Soon I'll be testing again, once the weather clears up.
the inline *circulating* heater is much more effective than the *non-circulating* kind.
the non-circ. one installed in the lower rad hose isn't very efficient at spreading the heat. i've read several accounts of people using the lower rad hose style - they can feel and hear the coolant boiling away in the hose, but it doesn't transfer past the (closed) thermostat very well.
my pick would be on the recirculating type that installs in the heater hose line.
That's why I've decided to keep my engine block heater plugged-in all the time.
literally all the time?
that may be overkill. 2 hours before driving is the most you should need to get the good effects (closed loop & o.d.). i aim for 1 - 1.5 hrs of plug-in time before i drive.
you know you can also get a block heater timer, eh? if you're on a regular schedule, they work great. and it saves some power & money in the long run.
Maybe a lack of planning on my part, but I don't really know when I'll be driving the car again during the day (I work from home and drive to the airport often, or to the post office). I could probably have it set up on a heavy-duty timer where it shuts-down at night, and comes on 1.5 hours before I leave in the morning for my daily routine (coffee run -- it's psychological -- I love driving, and I drive to the coffee shop before I start work in the morning to get into the work-flow mood).
By the way, I installed the OEM version that I ordered from my dealer. I've been accused of overpaying, but it came with helpful info for installation and it installed right into the drain plug (note: lots of coolant will drain -- get a sizable pan to collect it if you go that route, and follow proper technique for bleeding air from the cooling system).