NEVER do THIS to your Automatic Transmission Car | The Car Care Nut

**Walter** · November 27th, 2024 10:04 AM

Also thought this was the case before ... but they did a test and fuel consumption is the same when in Neutral or Drive at a stop light ... when you search online, most will advise leaving it in Drive and not shift to Neutral ... trying to understand why this is the case ... just doesn't make sense ... might have something to do with auto brake hold being more available nowadays ... for practical and safety reasons, still shifting to Neutral at a stop light for safety ...

Maybe it's also due to the new generation drivers shifting to Neutral every time the vehicle stops ...

**Motortrend** · November 27th, 2024 10:17 AM

Originally Posted by oj88

Wrong. Neutral is where the A/T is most "relaxed". Everything is free-wheeling, including the torque converter.

When in Drive and with the brakes applied and/or auto-hold activated, the torque converter is engaged, adding load to the system. Specifically, the impeller (engine side) is constantly trying to transfer power by pumping ATF to the turbine (transmission side), which is held stationary due to the brakes being applied. This constant churning of the ATF (stuck between a hard place and a rock) can raise the ATF temp somewhat. And because there's that viscous interface in the torque converter adding load to the engine, it increases fuel consumption.

Notice how the idle sags ever so slightly when you shift from Neutral to Drive? The torque converter is engaging and trying to move the car, but the brakes (or auto-hold) is preventing that from happening. This is like half-engaging the clutch while in 1st gear on an M/T with the brakes applied.

So, feel free to shift to Neutral during long stops. You're doing your A/T, engine, and yourself a favor.

This makes sense.

**Verbl Kint** · November 27th, 2024 10:40 AM

Originally Posted by Walter

Use P only when parking ... not a smart idea to use when at a stop light ... there's a reason it's labeled as P = Park ...

I wonder how much force a parking pawl can take when you get bumped from behind at a traffic light.

**oj88** · November 27th, 2024 10:43 AM

Originally Posted by Walter

Also thought this was the case before ... but they did a test and fuel consumption is the same when in Neutral or Drive at a stop light ...

Oh, but they do. Though not that significant, but they do add up.

I've done this experiment on two vehicles.... my old Civic 1.8 and my Innova 2.8 Diesel.

Civic 1.8 idle fuel consumption (Liters per Hour or LPH) when in Neutral vs Drive and with the A/C compressor engaged and disengaged:

Innova 2.8 Diesel idle fuel consumption when in Neutral vs Drive:
Neutral: 0.7 LPH

Drive: 1.0 LPH

So in both cars, gasoline and Diesel, the added fuel consumption is roughly 30% when you leave it on Drive when idling.

when you search online, most will advise leaving it in Drive and not shift to Neutral ... trying to understand why this is the case ... just doesn't make sense ... might have something to do with auto brake hold being more available nowadays ... for practical and safety reasons, still shifting to Neutral at a stop light for safety ...

Maybe it's also due to the new generation drivers shifting to Neutral every time the vehicle stops ...

The choice to shift to Neutral at a stop depends on the circumstances. Short stops, leave it on Drive. Long stops, put it in Neutral. Whether your stop is to be considered Short vs Long is subjective, but personally, I consider 90 seconds or longer to be "long enough" to warrant a shift to Neutral. It's not a hard rule because, again, it depends on the actual circumstances.

**carxynogen** · November 27th, 2024 10:50 AM

Originally Posted by Walter

Use P only when parking ... not a smart idea to use when at a stop light ... there's a reason it's labeled as P = Park ...

That's why I shift to N first and engage handbrake before going to Park.
So that all the loads are not in the P but on the handbrake.
2-3 mins sa stoplight, medyo ngalay na tapak brake.

I am still contemplating to shift to N, after oj88's explanation make sense.

**dr. d** · November 27th, 2024 11:10 AM

as someones already explained,
idle at D, with the brakes engaged, and the engine crankshaft rotates against a resistance. the brakes are also stressed.
idle in N, and the crankshaft rotates against a significantly lower resistance, and the breaks are not stressed so much.

**Walter** · November 27th, 2024 11:13 AM

Originally Posted by oj88

The choice to shift to Neutral at a stop depends on the circumstances. Short stops, leave it on Drive. Long stops, put it in Neutral. Whether your stop is to be considered Short vs Long is subjective, but personally, I consider 90 seconds or longer to be "long enough" to warrant a shift to Neutral. It's not a hard rule because, again, it depends on the actual circumstances.

This summarizes it well ... to add to this ... if you see the stop light just turn from green to red, then shift to Neutral ... when there is already a long line waiting at a stop light, leave it in Drive since chances are that the light is about to turn green ... unless there's a gridlock ...

From Drive, foot brake then Neutral then parking (hand) brake then release foot brake ... but do not shift to Park ...

**ice15** · November 27th, 2024 11:28 AM

just sharing...

ako din, I will always put the vehicle in neutral (then handbrake) kapag matagal akong maghihintay.

pero with our Zenix...

naka-pila ako to enter the parking (it was full) kaya I decided to put it in "N" tapos handbrake ako... when the engine was about to start, nag notify yung car to put the car in D... personally, di ko maintindihan why that happened... never experienced that before kapag nasa P yung shifter ko

**Motortrend** · November 27th, 2024 11:56 AM

Originally Posted by oj88

Oh, but they do. Though not that significant, but they do add up.

I've done this experiment on two vehicles.... my old Civic 1.8 and my Innova 2.8 Diesel.

So in both cars, gasoline and Diesel, the added fuel consumption is roughly 30% when you leave it on Drive when idling.

The choice to shift to Neutral at a stop depends on the circumstances. Short stops, leave it on Drive. Long stops, put it in Neutral. Whether your stop is to be considered Short vs Long is subjective, but personally, I consider 90 seconds or longer to be "long enough" to warrant a shift to Neutral. It's not a hard rule because, again, it depends on the actual circumstances.

30% is a significant difference. And yes, it adds up.

**labayds** · November 27th, 2024 12:12 PM

Originally Posted by ice15

just sharing...

ako din, I will always put the vehicle in neutral (then handbrake) kapag matagal akong maghihintay.

pero with our Zenix...

naka-pila ako to enter the parking (it was full) kaya I decided to put it in "N" tapos handbrake ako... when the engine was about to start, nag notify yung car to put the car in D... personally, di ko maintindihan why that happened... never experienced that before kapag nasa P yung shifter ko

Hybrid? If so, the hybrid battery cannot charge if the shifter is in N. It has to be in D or P for it to be able to charge.