Engine Temps - Coasting To a Stop - Fuelly Forums

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Old 04-07-2007, 09:28 AM   #1
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Engine Temps - Coasting To a Stop

Question for the hypermilers. I've been killing my engine as I coast to a stop when I approach a red light (was that a run on sentence?). Do you wait for your engine to warm up before doing this? Or start doing this immediatly?

I personally wait for it to warm up as I suspect that there's a warm up enrichment program and don't need to dump that extra fuel on start up. I was just curious if anyone had some insight on this
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Old 04-07-2007, 09:45 AM   #2
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I wait for it to warm up because I do not want to delay the car from reaching a point where its emissions become the least. If you P&G all the way and never warm the car up you are probably having horrible emissions.
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Old 04-07-2007, 09:52 AM   #3
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I bet the emissions of multiple cold starts are horrible, and it causes a lot of extra engine wear. Supposedly 90 percent of engine wear occurs during cold starts. So I wait at least a few minutes after the coolant is up to temp. Just because the coolant is up to temp doesnt mean the oil is.
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Old 04-07-2007, 10:12 AM   #4
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yeah i wait so that the engine is warm because cold starts use a ton of gas
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Old 04-07-2007, 11:10 AM   #5
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I wait for it to warm up because I do not want to delay the car from reaching a point where its emissions become the least. If you P&G all the way and never warm the car up you are probably having horrible emissions.
That would be interesting to see data on. I think I remember Dan saying that he was engine off over 50% on his commute. So what would the emissions be for that time that the engine off compared to on. At least here my exhaust temps close loop pretty fast usually by 100 yards. Once you're in closed loop is that's all thats required for emissions or is there more to it? Operational temps will give better FE(although the top 10 list is tons of engine off) but on the emissions what is required?
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Old 04-07-2007, 11:21 AM   #6
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It is about heating the cat up for emissions, not really getting to closed loop. I am not sure how long it takes, though.
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Old 04-07-2007, 11:47 AM   #7
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It is about heating the cat up for emissions, not really getting to closed loop. I am not sure how long it takes, though.
I don't know the EPA list cars and the amount of CHG in tons/year when you check the EPA figures. So if you drop the MPG figure by 30-40 % or more then doesn't it stand to reason that the total sum would be better, not necessarily equal, 30-40% might translate into 25-30% but still better. Less fuel has got to be better all the way around with todays modern engines. Just my thoughts I would be interested to here other views.

As far as multiple starts the first one is the only one that is done without previous oil circulation so the remaining ones would not be a problems. If it's a manual transmission you can bumps start. Even if you used the starter when was the last time you replaced one. I've had several cars with over 150k and never replaced a starter.
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Old 04-07-2007, 11:56 AM   #8
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It is listing, primarily, I think, c02 emissions, and not things like sulfurs and nitrogen oxides. But then again, I am not sure of. However, I do believe that a car does more than 30-40% of it's polluting during the warm up phase of a medium sized trip, so that extending that polluting phase to cut fuel use by 30-40% would not have a net benefit.
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Old 04-07-2007, 12:43 PM   #9
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My engine often doesn't even reach it's full operating temperature by the time I get to my destination when it's particularly chilly outside, so I normally EOC right away. My mpg on the SG drops like a stone when the engine is running at a stop.

The only time I leave the engine running 100% of the time is when it's REALLY cold out. Like when I NEED the heater to clear the frost from the inside of the windows. During those times, my FE drops dramatically. I should just install a fireplace with a chimney in my car when it's winter time. Can anyone say emissions?

I also have a general question for GS members: Why does the heat in my car turn cold when the engine is off? The vent still blows, but no heat. Surely the engine block is still hot when it's no running. Is there a way to make the air stay warm?
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Old 04-07-2007, 01:05 PM   #10
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I also have a general question for GS members: Why does the heat in my car turn cold when the engine is off? The vent still blows, but no heat. Surely the engine block is still hot when it's no running. Is there a way to make the air stay warm?
your heater core is like a small radiator. when you shut down the engine the coolant isn't moving anymore
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