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Android Users - Coming Soon! - Migrating from aCar 4.8 to 5.0

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Old 09-30-2007, 07:53 PM   #11
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Originally Posted by rh77 View Post
By the way, welcome to GasSavers...

Nice car! This year, we get the Astra as a "Saturn Astra", but without the diesel option.

I think you may be our first Portuguese member, so a special welcome is in order!

RH77
Thank you very much!
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Old 09-30-2007, 07:55 PM   #12
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Originally Posted by KARR View Post
On a forum about cars it's in discussion if driving in neutral will get 0 L/100 km or "infinite" MPG.
(emphasis mine, not the OP's)

The answer to the question you asked is no, it doesn't happen that way in most cars. However:

Driving in gear can sometimes give you "infinite" MPG (no fuel), if/when you have sufficient forward momentum (to keep your RPMs up), and you have your foot off the gas (i.e. "no throttle"). You will slow down in this arrangement (unless going down a steep enough hill), because you are essentially dragging down your forward wheel motion with the effort to spin your engine and transmission. However, in many cars, the ECU (engine computer) will sense that you don't need gas for your current driving conditions, and cut the fuel entirely.

However, that's not what happens when you are in neutral. In neutral the transmission disconnects the wheels from the engine. Since the wheels are no longer connected to the engine, your forward motion of the wheels can't spin the engine to keep up its RPMs. As a result, your car would "die", if fuel weren't added to maintain "idle". It's true that the fuel to idle often isn't all that great. And its also true that you can sometimes coast sufficiently further in neutral (vs "in gear") to make that extra fuel cost a good bargain. But you still will not have "infinite MPG" when you are in neutral, as you will be paying the fuel to maintain idle.

BTW: I've been known to do both approaches (in gear "infinite MPG" coasting, and neutral "pay for idle" coasting), depending upon the situation. If I'm going to still have enough momentum to get to my goal (for example, the upcoming red light) with "in gear" (zero fuel) coasting, than that is the approach I take. However, if my RPMs are too low for to maintain fuel shutoff and/or I need to go further/faster, I'll often just pay the slight fuel cost for "idle", and coast in neutral (out of gear). And I've even been known to start off coasting in 5th (high gear), and switch to neutral coasting (and thereby lengthen my coasting distance) as soon as I slow down enough for the fuel cutoff to shut off. Because as soon as my RPMs drop enough to lose my "fuel cutoff", I'm using fuel anyway. And if I'm going to pay some fuel cost anyway, I figure I might as well limit the fuel to just "idle" costs, and go for as long of a coast as traffic patterns allow...
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Old 09-30-2007, 08:27 PM   #13
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Quote:
Originally Posted by DracoFelis View Post
(emphasis mine, not the OP's)

The answer to the question you asked is no, it doesn't happen that way in most cars. However:

Driving in gear can sometimes give you "infinite" MPG (no fuel), if/when you have sufficient forward momentum (to keep your RPMs up), and you have your foot off the gas (i.e. "no throttle"). You will slow down in this arrangement (unless going down a steep enough hill), because you are essentially dragging down your forward wheel motion with the effort to spin your engine and transmission. However, in many cars, the ECU (engine computer) will sense that you don't need gas for your current driving conditions, and cut the fuel entirely.

However, that's not what happens when you are in neutral. In neutral the transmission disconnects the wheels from the engine. Since the wheels are no longer connected to the engine, your forward motion of the wheels can't spin the engine to keep up its RPMs. As a result, your car would "die", if fuel weren't added to maintain "idle". It's true that the fuel to idle often isn't all that great. And its also true that you can sometimes coast sufficiently further in neutral (vs "in gear") to make that extra fuel cost a good bargain. But you still will not have "infinite MPG" when you are in neutral, as you will be paying the fuel to maintain idle.

BTW: I've been known to do both approaches (in gear "infinite MPG" coasting, and neutral "pay for idle" coasting), depending upon the situation. If I'm going to still have enough momentum to get to my goal (for example, the upcoming red light) with "in gear" (zero fuel) coasting, than that is the approach I take. However, if my RPMs are too low for to maintain fuel shutoff and/or I need to go further/faster, I'll often just pay the slight fuel cost for "idle", and coast in neutral (out of gear). And I've even been known to start off coasting in 5th (high gear), and switch to neutral coasting (and thereby lengthen my coasting distance) as soon as I slow down enough for the fuel cutoff to shut off. Because as soon as my RPMs drop enough to lose my "fuel cutoff", I'm using fuel anyway. And if I'm going to pay some fuel cost anyway, I figure I might as well limit the fuel to just "idle" costs, and go for as long of a coast as traffic patterns allow...
Amazing explanation! Thanks DracoFelis!
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