downside of ZZZZZZ
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From: LaLaLand
Originally Posted by EddNog
When you're in gear and off the throttle, it does not apply any fuel at all. If you are disengaged from gear (on the clutch) or in neutral, the engine applies fuel to maintain idle. That's why staying in gear when coasting uses less fuel than leaving it in neutral.
It is also illegal in Europe to coast around in neutral, but there are other reasons for that.
As far as what I'm getting, I'm mixed city/highway and get 20.5 MPG and couldn't be happier with it; that's better than we get on my dad's Legacy 2.5GT and better, in fact, than I used to get on my Scion tC that I traded for this car, which is entirely due to gearing (way too short on the 5MT tC). For a 3.5liter motor that cranks out 306 peak horsepower and still gives decent midrange torque, to me, 20 MPG mixed cycle is great!
-Ed
EDIT: PS I agree with the other posters in terms of ways to save fuel; try to drive WOT when accelerating and shift short but do not lug (i.e. shift under 3,000 whenever possible--I generally shift right at 2,000 RPM). Driving WOT at low RPM reduces pumping losses, but obviously going WOT in 1st gear guarantees shifting crazy soon. Also, even though you may be in the interest of saving fuel costs, absolutely do not lug your car by shifting too short--the damaged caused in the long run will cost you more than burning a little extra gas to shift appropriately. An extreme example of lugging is being at street crawling speed, upshifting to 6th gear, putting the engine at the 500rpm level and then flooring it to accelerate--lugging is bad because it causes oil starvation from oil pump velocity.
It is also illegal in Europe to coast around in neutral, but there are other reasons for that.
As far as what I'm getting, I'm mixed city/highway and get 20.5 MPG and couldn't be happier with it; that's better than we get on my dad's Legacy 2.5GT and better, in fact, than I used to get on my Scion tC that I traded for this car, which is entirely due to gearing (way too short on the 5MT tC). For a 3.5liter motor that cranks out 306 peak horsepower and still gives decent midrange torque, to me, 20 MPG mixed cycle is great!
-Ed
EDIT: PS I agree with the other posters in terms of ways to save fuel; try to drive WOT when accelerating and shift short but do not lug (i.e. shift under 3,000 whenever possible--I generally shift right at 2,000 RPM). Driving WOT at low RPM reduces pumping losses, but obviously going WOT in 1st gear guarantees shifting crazy soon. Also, even though you may be in the interest of saving fuel costs, absolutely do not lug your car by shifting too short--the damaged caused in the long run will cost you more than burning a little extra gas to shift appropriately. An extreme example of lugging is being at street crawling speed, upshifting to 6th gear, putting the engine at the 500rpm level and then flooring it to accelerate--lugging is bad because it causes oil starvation from oil pump velocity.
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From: Portland, OR
At BEST the fuel consumption would be the same whether coasting or in gear. But it seems pretty logical to me that coasting in gear would burn more fuel. If your foot is off the throttle the throttle position (idle) is the same whether in gear or coasting. However, if you're in gear the engine will be turning more RPM and burning whatever the idle mixture is at a higher rate. I'm relatively certain my car doesn't just turn off when I'm coasting in gear. If you want to know what it would be like if it did, just coast down a hill somewhere in gear and turn the ignition off. Just be prepared to lose your power assist on steering and brakes!! And don't turn the key so far that you lock your steering. I know I know, that should be obvoius. But then again so should the fuel consumption issue.
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From: Scarsdale, NY
It does not die because the car is in gear and still moving. Idling fuel is not applied until the engine is below a certain RPM. There is a maximum amount of fuel set for idling, so it will not apply more than that to maintain an idle, but it does not apply that fuel unless engine speed is at or below idle. So for example you're cruising on the highway in 6th gear and completely let off the throttle the engine does not die because it's kept in motion by the car being in gear. As soon as you hit the clutch, the engine's rpms drop because throttle is not applied, but as the rpm nears stall, idling fuel is appled and then the engine sustains idle, until you apply fuel again and/or engage gear again at which point RPMs will rise back up to match speed through the drivetrain to the wheels. That is how the idle works.
-Ed
-Ed
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From: Portland, OR
Here's a safer test the turning the engine off while coasting down a hill. Find a nice flat parking lot. Get your car rolling in first gear....make sure the clutch is all the way engaged (I'm assuming MT). Now take your foot off the gas and coast. What happens?
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From: LaLaLand
Originally Posted by EddNog
It does not die because the car is in gear and still moving. Idling fuel is not applied until the engine is below a certain RPM. There is a maximum amount of fuel set for idling, so it will not apply more than that to maintain an idle, but it does not apply that fuel unless engine speed is at or below idle. So for example you're cruising on the highway in 6th gear and completely let off the throttle the engine does not die because it's kept in motion by the car being in gear. As soon as you hit the clutch, the engine's rpms drop because throttle is not applied, but as the rpm nears stall, idling fuel is appled and then the engine sustains idle, until you apply fuel again and/or engage gear again at which point RPMs will rise back up to match speed through the drivetrain to the wheels. That is how the idle works.
-Ed
-Ed
By this logic, you pretty much contradict everybody's statement when they suggest the OP to shift at lower RPM.
Last edited by GonZ; Jul 10, 2007 at 01:31 PM.
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From: Portland, OR
Originally Posted by EddNog
It does not die because the car is in gear and still moving. Idling fuel is not applied until the engine is below a certain RPM. There is a maximum amount of fuel set for idling, so it will not apply more than that to maintain an idle, but it does not apply that fuel unless engine speed is at or below idle. So for example you're cruising on the highway in 6th gear and completely let off the throttle the engine does not die because it's kept in motion by the car being in gear. As soon as you hit the clutch, the engine's rpms drop because throttle is not applied, but as the rpm nears stall, idling fuel is appled and then the engine sustains idle, until you apply fuel again and/or engage gear again at which point RPMs will rise back up to match speed through the drivetrain to the wheels. That is how the idle works.
-Ed
-Ed
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From: The Lou
I get 18 after switching to 10w30. lost about 2-4 mpg by going with the heavier cold weight. I'm sure I'll get better once I switch back to 5w30 next time around. was getting about 20-22 all around driving.
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From: Little Elm, TX
Coasting in gear uses more fuel... we had the same argument on scionlife a while back. Here's the link to the thread. My login name is FlintGauge just like on my350z.
http://www.scionlife.com/forums/view...gear&&start=20
http://www.scionlife.com/forums/view...gear&&start=20
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From: Scarsdale, NY
Originally Posted by noir06
At BEST the fuel consumption would be the same whether coasting or in gear. But it seems pretty logical to me that coasting in gear would burn more fuel. If your foot is off the throttle the throttle position (idle) is the same whether in gear or coasting. However, if you're in gear the engine will be turning more RPM and burning whatever the idle mixture is at a higher rate. I'm relatively certain my car doesn't just turn off when I'm coasting in gear. If you want to know what it would be like if it did, just coast down a hill somewhere in gear and turn the ignition off. Just be prepared to lose your power assist on steering and brakes!! And don't turn the key so far that you lock your steering. I know I know, that should be obvoius. But then again so should the fuel consumption issue.
-Ed
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From: Portland, OR
Originally Posted by EddNog
Coasting in gear does not burn more fuel unless you're on on the throttle, which is an oxymoron because then you're not coasting. The amount of fuel is proportional to the amount of air going in (on the rich side from stoichiometric (SIC) for safety, as per factory standards), and not proportional to the rate of engine rotation. Higher rates of engine rotation allow more fuel and air to be applied, which is why opening the throttle at a higher RPM burns more fuel than applying the same amount of throttle at a lower RPM. The reason why revving higher uses more fuel is because the engine can take more air and thus more fuel in ratio for the same amount of throttle opening compared to lower RPMS. You're also dealing with having to overcome greater amounts of internal engine friction for the same amount of distance traveled at a higher RPM. Coasting at 60mph in 6th gear with no throttle application uses no more fuel than coasting at 60mph in 4th gear, but in 4th gear the car will engine brake harder due to geater friction and vacuum effect--that's also why engine braking is harder in the higher rev range in any gear.
-Ed
-Ed
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From: Little Elm, TX
This is from the other thread I mentioned before. This is Dr Isotope.
paul34 wrote:
Some questions for you, good sir:
Do you know how a bump start works?
Why you can overrev into redline when doing an incorrect downshift?
Why the car will stop moving if the engine is off, and handbrake is down, and you left the car in gear?
Why an engine stalls when the wheels stop moving?
____________________________________________________________ ____________________________
Posted By DrIsotope
None of these have anything to do with better gas mileage in neutral vs. in gear. They just confirm the fact that the engine and the transmission are physically connected. Do they imply greater efficiency? Just the opposite, actually.
A car traveling downhill in neutral has to overcome 2 basic forces: air resistance, and friction between the tires and the road.
A car traveling downhill in gear has to overcome: air resistance, friction between tires and the ground, rotating mass, and the engine's own compression.
The wheels are not moving the pistons. The wheels are spinning at a rate greater than the engine is supporting; their rotational rate is increase by the action of the car's inability to fight gravity: it rolls downhill. This is why the fuel mileage going downhill is better than going uphill. Less load, so the car uses less fuel to move. But it's still using fuel at a rate greater than idle. And to think otherwise is ridiculous.
So no matter how you slice it, you will use less fuel coasting downhill than rolling in gear-- because you've effectively removed the engine from the equation. It is neither trying to speed the car up or slow it down. It's dead weight, consuming only what fuel it needs to run it's own life-support systems (charging and cooling).
_________________
Some questions for you, good sir:
Do you know how a bump start works?
Why you can overrev into redline when doing an incorrect downshift?
Why the car will stop moving if the engine is off, and handbrake is down, and you left the car in gear?
Why an engine stalls when the wheels stop moving?
____________________________________________________________ ____________________________
Posted By DrIsotope
None of these have anything to do with better gas mileage in neutral vs. in gear. They just confirm the fact that the engine and the transmission are physically connected. Do they imply greater efficiency? Just the opposite, actually.
A car traveling downhill in neutral has to overcome 2 basic forces: air resistance, and friction between the tires and the road.
A car traveling downhill in gear has to overcome: air resistance, friction between tires and the ground, rotating mass, and the engine's own compression.
The wheels are not moving the pistons. The wheels are spinning at a rate greater than the engine is supporting; their rotational rate is increase by the action of the car's inability to fight gravity: it rolls downhill. This is why the fuel mileage going downhill is better than going uphill. Less load, so the car uses less fuel to move. But it's still using fuel at a rate greater than idle. And to think otherwise is ridiculous.
So no matter how you slice it, you will use less fuel coasting downhill than rolling in gear-- because you've effectively removed the engine from the equation. It is neither trying to speed the car up or slow it down. It's dead weight, consuming only what fuel it needs to run it's own life-support systems (charging and cooling).
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From: Little Elm, TX
It's absolutely insane to think that engine braking is more effecient than neutral coasting. The tC idles a 800 RPM after finishing it's warm up dance( correct me if i'm wrong on the idle, it's been a while since I drove a tC). So if you're traveling down a hill at 45 MPH, the tC will be running at about 2K RPM, which is 1200RPM more than Idle , which means the engine is demanding that much more fuel to keep going. IF youre theory of the fuel cut off and the wheel powering the engine is correct, go drive down a hill, leave the car in gear, and turn off the car. You're driving wheels will lock up so fast and send you all over the road... why, becuz the engine stops spinning, so the wheels stop spinning. If you don't believe me, go try it, and then tell me how you screwed up your car in the process, cuz it will. Engine braking is hard on the engine and causes excess wear and tear on it. The use of engine braking was introduced when cars still had drumb breaks which quickly overheated and fade out, so the drivers would downshift to slow down the car, to aviod overheating the breaks and crashing into the bushes when the faded. Todays modern cars have advanced disc brakes with vented rotors, Brake force distribution, ABS, and high heat capacity calipers, with pads that are designed to wear out and be replaced. Please, PEOPLE,just use your brakes. It's better for you milage and your engine. To say that you want to save your breaks and use engine breaking is like saying you want to power shift so you don't wear out your clutch...
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From: Portland, OR
LOL!!!! After doing some independent research Ed is right boys. Oh man.....I hate it when I'm wrong. Especially when I've been so emphatic. Kudos to you for sticking to your guns Ed. I can at least say I admit when I'm wrong as painful as it is. It's not the first time and probably won't be the last. Thanks, Ed. I learned something new today.
Although, the more I read.....it looks like it depends on the car. Some do and some don't. I've seen references to some cars where they did that for a while, but did away with it in order to keep the cats up to temp etc.....so maybe yes, maybe no. But some are a definite yes.
Although, the more I read.....it looks like it depends on the car. Some do and some don't. I've seen references to some cars where they did that for a while, but did away with it in order to keep the cats up to temp etc.....so maybe yes, maybe no. But some are a definite yes.
Last edited by noir06; Jul 10, 2007 at 01:50 PM.
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From: Scarsdale, NY
I cannot find my source; as such, I'll admit that I was wrong on this issue. I do not know why I was initially convinced that I had a solid source for this--probably because I've simply read too many arguments on the issue. I thoroughly apologize for any confusion I may have caused.
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From: Scarsdale, NY
Originally Posted by noir06
LOL!!!! After doing some independent research Ed is right boys. Oh man.....I hate it when I'm wrong. Especially when I've been so emphatic. Kudos to you for sticking to your guns Ed. I can at least say I admit when I'm wrong as painful as it is. It's not the first time and probably won't be the last. Thanks, Ed. I learned something new today.
-Ed
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From: Scarsdale, NY
Tell you guys what; I'll just try it for you later today on my way home. I'll find a downhill section I can just stop the car on, pull up the hand brake, turn the key to ACC, and then let off the hand brake slowly. My experience in the past is that it doesn't take much to get a car rolling, even with the engine off, but it will take a concrete test to know for sure. I can also start at the top of the hill, roll to 15mph, get to the straight part of the hill, and turn the key to ACC to see what happens. What I'll be looking for is A) if the drive wheels lock up and B) if the amount of engine brake effect increases or decreases when the engine is deactivated. I will also keep an eye out for deactivated accessories (brake assist, steering assist). I don't mind doing it since I have controlled places to try it. My past experience is that internal friction in the engine isn't sufficient to hold a car still on a particularly steep hill, which the first test will verify. Remember also that the drivetrain is a torque multipler/divider. I can run the first test in first gear. If the car doesn't move, I'll re-engage the hand brake, switch to 6th gear, and then ease off the hand brake again--I'm quote positive the car will roll very easily in 6th. I can also run the second test in various gears to compare, but it'll be hard to do it in 6th gear because I'd have to get the car moving pretty fast and my test hill isn't long enough to do it safely, so I'd have to try it in 2nd gear and perhaps again in 4th gear.
-Ed
-Ed
What your saying doesn't make any sense.
When your coasting in gear regardless if you apply throttle or not, your engine is still running. Meaning there is still combustion being conducted....So i guess by your reasoning, combustion is happening with oxygen only right? cause oxygen likes to self ignite itself.....
When your coasting in gear regardless if you apply throttle or not, your engine is still running. Meaning there is still combustion being conducted....So i guess by your reasoning, combustion is happening with oxygen only right? cause oxygen likes to self ignite itself.....
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From: NYC
Ed is right. When I had my 86 300zx it would constantly monitor mpg, not average it out like today's z. Anyway whenever I would let off the gas, in gear, for at least 5 seconds the monitor would read 99 mpg, in other words no gas being used at that particular time. Gotta love MT.
Last edited by ray427; Jul 10, 2007 at 03:07 PM.