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Old 02-20-2009, 08:06 PM   #71 (permalink)
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Sort of on topic here, I had an opportunity today to compare fuel economy with the engine cold vs warmed up. Reason: I forgot my keys and phone at home. Anyway, on a cold day my 5.5 mile drive to work usually results in about 22-23 MPG. The engine reaches normal operating temp about halfway through. Before I left for work for the second time (with the car now fully warmed up) I reset the SGII, and then checked it when I got to work. Result: 27 MPG. A rough calculation says that a $33 block heater would pay for itself in two years, at current fuel prices. Although that assumes a fully warmed up car, and from what I've read this only gets the coolant up to around 150*F. But throw in the comfort factor and the reduced CO2 output and it's a no brainer.

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Old 02-21-2009, 03:09 PM   #72 (permalink)
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Quote:
Originally Posted by Formula413 View Post
Sort of on topic here, I had an opportunity today to compare fuel economy with the engine cold vs warmed up. Reason: I forgot my keys and phone at home. Anyway, on a cold day my 5.5 mile drive to work usually results in about 22-23 MPG. The engine reaches normal operating temp about halfway through. Before I left for work for the second time (with the car now fully warmed up) I reset the SGII, and then checked it when I got to work. Result: 27 MPG. A rough calculation says that a $33 block heater would pay for itself in two years, at current fuel prices. Although that assumes a fully warmed up car, and from what I've read this only gets the coolant up to around 150*F. But throw in the comfort factor and the reduced CO2 output and it's a no brainer.
My back-of-napkin calculations show that a block heater will actually cost you money. If you drive to work 5.5 miles @ 23 MPG, and spend $2 for fuel, you will spend 48 cents one way. If you can do it at 27 mpg you will spend 41 cents. I'm assuming that you wouldn't be able to plug your heater in at work, so it looks like you would save about 7 cents per day in fuel costs. My best guess is that it takes about 10 cents of grid electricity to warm your car up in the morning, so you'd be spending 3 cents a day. If you could plug in your car at work you'd be saving 4 cents.

Now you also have to consider the facts that a block heater won't heat your car to operating temps and it will certainly be much less effective in the summer months, so I don't think that there would be any payback at all for your situation if you were allowed to plug it in at work. Besides, if you leave it plugged in all day at work or at home instead of just when you needed it, you'll end up wasting huge amounts of energy, so you'd have to buy a 15 amp timer or just be really good at pluggin it in an hour before you want to drive. If you want one for comfort that's one thing but I doubt you'll really save any money by using one. If you had a longer commute it might pay off.

Does anyone have any real data on reduced wear and tear by using a block heater? That could be the icing on the cake argument to make one of these make sense for most people.
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Old 02-22-2009, 02:17 AM   #73 (permalink)
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Before I even got this reply it occurred to me that I hadn't accounted for the cost of the electricity. Although even without any cost savings there is still the added comfort and reduced emissions. So that's something anyways.

I'm reasonably certain there would still be a FE increase from using a block heater in warm weather as well, since the engine would not run as rich and would enter closed loop more quickly.

Then there's the fact that another surge in fuel prices would change the math on this significantly, and possibly make it profitable to run the block heater.
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Old 12-22-2009, 12:46 PM   #74 (permalink)
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I've been away for a while but I figured I'd respond to my own criticism with some real numbers. I bought a Prius a few months ago and installed a block heater last week. Now my numbers here aren't scientific (yet) but by my observance I can go from about 50 MPG to about 55 MPG by running the block heater for 2 hours in the morning. It has a 400 watt element, and cost $50. I drive right at around 15,000 miles per year. If I assume that fuel costs $2.50 per gallon and electricity costs $0.10 per kWh, I get a daily cost of about $0.08 in electricity to save about $0.18 in gasoline. So it would take about 500 days to pay off the cost of the heater. Not too bad, and I'd much rather pay for Ketucky coal than imported gasoline.
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Old 12-22-2009, 01:45 PM   #75 (permalink)
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i pay for what equates to a carbon offset to the electric company to guarantee my money goes to solar/garbage/wind production rather than coal. I get my electric at $.03/kwh before 7am and there is simply nothing like getting in your car in 5 degree weather and having warm air blowing.
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Old 12-31-2009, 12:34 AM   #76 (permalink)
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Quote:
Originally Posted by MetroMPG View Post
Ask and ye shall receive!



From: Experiment: how long should a block heater be plugged in? - MetroMPG.com

I haven't tried to measure impact on fuel economy because I didn't think I could control enough variables to get meaningful results.
What do you think about letting the car cool to ambient over night, and check the mileage from a cold start over known course? Then do it again once the car is up to running temp. May not be total accurate, but over the course of a couple mornings you should see a pattern.

How consistent is the first 5 to 10 miles of your commute?

One other argument for using a block heater (and or oil pan) is that the oil flows and splashes better when warm this means oil coating your cylinder walls quicker, to your bearings quicker, and bathing your valves quicker. Which means your engine going to last longer. On some mornings it also means your engine will start at all.

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Last edited by bestclimb; 12-31-2009 at 12:40 AM..
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