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Junior Member
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154 Posts
Discussion Starter #1
It's winter time again. Thought I would post this up since the topic will come up again. I did this test a few years ago.

This morning I plugged the block heater in. My Scangauge read 39 degrees.

1 hour later it was 80 degrees.

2 hours later was 94 degrees.

3 hours later it was 103 degrees.

4 hours later it was 110 degrees.

5 hours later it was 116 degrees.

Yes, 39 isn't that cold to start, but was interesting to see that it went from 39 to 80 in an hour.

Currently my oil temp in hour 3 is 77 degrees. It was 40 at starting point.

Oil temp after 4 hours is 91 degrees.
A lot of folks use a timer to control costs and use for when the truck is needed daily.
 

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Senior Member
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1,324 Posts
I set my timer to come on 2 hours before I would need to go out and plow and 2 hours before I may need to plow when I get home. IMHO anything more than 2 hours is a waste of juice.
 

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Great post Sean - thanks.

One idea to throw out there. It just doesn't get cold enough here for me to need the block heater for start-ups, but I wonder if it wouldn't be cost justified to use it for an hour or two each morning - at least when the temps drop below 50 ...... I wonder if I wouldn't get some improvement in fuel economy by burning less diesel just to get block temps up. At 1000 watts and $0.1 / KWh for 2 hours that is $.20 each morning, or $5 - $6 a month. I use apprx 100 gallons of fuel each month, so I probably wouldn't notice it unless the extra heat put the controls in a more efficient mode right off the bat.

Anyway, just thinking out-loud. My fuel economy takes a beating on the lie-o-meter until the engine warms up.
 

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I would think there is a positive correlation by achieving operating temp efficiency sooner. Definitely depend on your drive during warm up.
One reason I plug in even if it's not super cold is so the beast warms up sooner. Mainly to reduce wear and tear on cold engine and tranny to push snow. Last winter was brutal I plow some neighbors for fun/ neighborly and it turned into a full time job just about everyday.
 

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Junior Member
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Discussion Starter #5
Interesting question Mark.

When I plug in for a few hours in the morning, I can pretty much start and go. After work, I need to idle a long time to get the motor warmed up for my 50 yard drive to the first traffic I need to jump into.

My winter mileage really drops, not so much the fuel change, but the darn idle time when leaving work.

We all have different variables we work with. Some of us can drive a few miles with low boost, others may have to boost higher sooner. Seems I recall topics of keeping boost low until the engine is warmed up.(Like under 10) Sometimes that is hard to do, given our circumstances.
 

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Interesting about the boost. My situation is such that I really don't idle it at all, even in the winter. Just doesn't get that cold - rarely below 30 degrees. I do take it easy until the engine is fully warmed up though.
 

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Curmudgeon
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472 Posts
When I used to commute 30 miles to work I played with a study to see if plugging in when 32f and lower would improve my mpg. It does a little with a timer I would set for 2-3 hrs before leaving. Sorry but I did not keep the spreadsheet, but for those of you from TDS may remember I kept a pretty intensive record of fuel mileage and factors.

Here was another thing I found, and maybe this was due more to my driving conditions of highway, flat road, and steady speed environment. A lot of us have noticed fuel mileage drops off during the winter, something that we normally associate with winter blend fuel. The other thing some of us notice is that coolant temp also runs a few degrees lower (commuting, low weight).

A number of years I still had a source of summer blend fuel well into January and would still see a reduction in mpg during the coldest days/weeks. By doing the old truck trick of partially blocking my radiator with a FedEx box I got my ECT back to normal without overheating (removed if heavy load) and my fuel mileage went back up to normal. I still do this but use a plastic sheet rather then cardboard as the cardboard does not like to get wet.

Again, this is with a few miles of local road and up on the parkway for steady state 65mph for 25 miles.
 

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Interesting, looks like two hours would be just about right. I wonder what kind of readings you'd have when the O.S. temps were in the teens or lower.
Does leaving the heater controls in the Defrost setting clear the windshield? I know on older vehicles with cable operated controls it would, was a handy benefit as well.
 
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