Hypermiling Newbie!

[Flakbadger]

Originally Posted by riva2model64

The argument of the writer seems to be that when a modern car coasts, the fuel injectors are off, so you are only experience engine resistance. When you shift into neutral, the fuel injectors turn back on to keep the engine in idle.

Okay so I drive a manual transmission, which is different... But in-gear coasting is 999MPG (actually infinite), which is just engine resistance. Neutral coasting with the engine idling is somewhere around 200MPG at ~40MPH.
So neutral coasting in an automatic, even with the engine still running, SHOULD give you pretty impressive MPG figures for the length of the coast.

[UltArc]

Originally Posted by Flakbadger

Okay so I drive a manual transmission, which is different... But in-gear coasting is 999MPG (actually infinite), which is just engine resistance. Neutral coasting with the engine idling is somewhere around 200MPG at ~40MPH.
So neutral coasting in an automatic, even with the engine still running, SHOULD give you pretty impressive MPG figures for the length of the coast.

It seems like GPH should be looked at, and compared to the amount of time for the in gear and in neutral.

That is, I imagine being in gear (with injectors off) still uses SOME fuel, and it will take longer to get somewhere (with the added engine resistance).

It makes sense to me- hope I am not mistaken again lol

[riva2model64]

I'm rather new to hypermiling, but what you say makes sense to me as well. I feel like if one truly wanted to know and had the equipment and methodology, they would have to know the gph of their engine in neutral. The only thing slowing down the car in this case is tire rolling resistance which is pretty negligible, and air resistance which is negligible at lower speeds.

When coasting in gear with the injectors off, I don't think it uses any fuel, however you lose speed due to the added drag of the engine being connected to the drive wheels.

Therefore, without recording any test data, I hypothesize that coasting to a red light or stop sign is far more efficient while coasting in gear vs. coasting in neutral.

I also hypothesize that given a situation where one will coast, then step on the gas again, coasting in neutral may potentially be more fuel efficient than coasting in gear because one will have to accelerate less due to a lower loss in MPH coasting in neutral. Though, without knowing the numbers, either form of coasting may be more efficient depending on the situation. One would also need to know when the ECU turns off the fuel injectors.

[Flakbadger]

Originally Posted by UltArc

That is, I imagine being in gear (with injectors off) still uses SOME fuel, and it will take longer to get somewhere (with the added engine resistance).

Actually, it uses 0 fuel. Looking at GPH, once my ultragauge goes into open loop, I'm using no fuel at all... and in my car, the displacement is so small that 5th gear really does not hold you back all that much. It does, but not like my old 4-liter Ranger did. Don't get me wrong, I understand your point and agree with you, I'm just sayin; I can coast pretty damn far in 5th.

Originally Posted by riva2model64

they would have to know the gph of their engine in neutral. The only thing slowing down the car in this case is tire rolling resistance which is pretty negligible, and air resistance which is negligible at lower speeds.

Speaking again about my car, I idle at .13-.15gph, depending on whether my lights are on or not. It only takes a moment for my fuel consumption to drop to that level when shifting from gear to neutral. As for air resistance, if I recall correctly, aero drag still accounts for 30+% of your fuel used at speeds below 40 MPH.

Originally Posted by riva2model64

When coasting in gear with the injectors off, I don't think it uses any fuel, however you lose speed due to the added drag of the engine being connected to the drive wheels.

Therefore, without recording any test data, I hypothesize that coasting to a red light or stop sign is far more efficient while coasting in gear vs. coasting in neutral.

I also hypothesize that given a situation where one will coast, then step on the gas again, coasting in neutral may potentially be more fuel efficient than coasting in gear because one will have to accelerate less due to a lower loss in MPH coasting in neutral. Though, without knowing the numbers, either form of coasting may be more efficient depending on the situation. One would also need to know when the ECU turns off the fuel injectors.

This all sounds pretty good to me

Cheers

~Matt

[UltArc]

Originally Posted by Flakbadger

Actually, it uses 0 fuel. Looking at GPH, once my ultragauge goes into open loop, I'm using no fuel at all... and in my car, the displacement is so small that 5th gear really does not hold you back all that much. It does, but not like my old 4-liter Ranger did. Don't get me wrong, I understand your point and agree with you, I'm just sayin; I can coast pretty damn far in 5th.



Speaking again about my car, I idle at .13-.15gph, depending on whether my lights are on or not. It only takes a moment for my fuel consumption to drop to that level when shifting from gear to neutral. As for air resistance, if I recall correctly, aero drag still accounts for 30+% of your fuel used at speeds below 40 MPH.



This all sounds pretty good to me

Cheers

~Matt

Don't get you wrong? I am rarely offended on this forum! I prefer this one because in my head, I think everyone is being polite and giving info for the better of everyone. I do appreciate your actual data on what was just a thought of mine. I would like to see how common that is, if other vehicles behave the same way.

If I put that clutch in [to coast], the kill switch gets flipped-I try to do as little engine on coasting as possible. And I imagine it is possible standard and auto behave a bit different. I don't know either way, just a thought.

[elhigh]

Originally Posted by mcrews

Help me.........do you tow with 'engine on'?????????

Does this thread talk about driving w/ 'engine off'?????????

Then PLEASE EXPLAIN the relevance.

THis pops up every time some asks about ENGINE ON COASTING IN NEUTRAL

There is NO CONECTION between the two.

There is a connection: the towing they're talking about is towing the car, not using the car to do the towing. Pulling the car with its drive wheels on the ground will cause part of the transmission to turn; some transmissions are safe to be spun by the wheels indefinitely because of how their lubrication systems are set up, others are not.

The best place to look for information on this is on RV sites. Pulling a dinghy vehicle around (also called flat towing) is a pretty quick way to utterly destroy the drivetrain of your dinghy if it can't take it, it's way far back there completely hidden behind the tow vehicle, you'd never see if something went awry. It's also why you often see compact 4x4 dinghy vehicles, just shift the transfer case into neutral and (usually) no further worries about the drivetrain, manual or automatic.

NOTE: the linked article points out that no Toyota automatic tranny is good for flat towing. That includes the OP's Camry, so that's at least one question answered.