Overdrive or not

**oj88** · June 23rd, 2018 06:44 PM

Originally Posted by Walter

Most modern vehicles will cut-off fuel when accelerator pedal is not pressed ... regardless of the transmission settings / status ... that is why coasting in neutral actual consume more fuel in modern vehicles ...

It's not a universal feature available in D. Different manufacturers, models, generations, price point etc., have different nuances in shift behavior and programming/intelligence.

Most A/T will just free-wheel (one-way clutch) or shift to the highest gear when the gas pedal is released while the vehicle is at speed with the O/D turned ON (one way or another). This prevents the vehicle from losing momentum while cruising on a highway due to engine braking. With the engine effectively de-coupled from the transmission, fuel is still required to keep the engine running at idle or high idle.

The engine brake effect is actually much preferred on slower roads (ie. City or in less than ideal traffic) for the reasons I already presented. But mainly, typical city driving prevents most vehicles from going faster than 60-80kph before the next traffic stop or bottle neck is reached. With the lock-up clutch still engaged (O/D off), it affords some level of engine braking as soon as you release the gas pedal. The vehicle momentum keeps the engine running while the resulting engine drag makes for less wear on the brakes.

In fairness to your position on this, there are vehicles that may have other sensors or intelligence to detect uphill and downhill driving and adjusts the A/T behavior accordingly without driver intervention. But again, this is not a universal feature and it is still best to follow manufacturer recommendations.

From the Honda user manual, they have this to say:

D3 - This position is similar to D, except only the first three gears are selected. Use D3 when towing a trailer in hilly terrain, or to provide engine braking when going down a steep hill. D3 can also keep the transmission from cycling between third, fourth, and fifth gears in stop-and-go driving.

**Walter** · June 25th, 2018 10:59 AM

Originally Posted by blackmoon06

When shifting from D to 2 do i have to put off my OD? Thanks po mga bro/sis sa sasagot.

No need ... it's really best to just leave overdrive on ... no need to overthink it ... OD is just there if you want to overtake (or going uphill) and need to downshift ... that's all there is to it ...

**Walter** · June 25th, 2018 11:01 AM

That's why I indicated modern vehicles with modern engine designs ... as to what year that is would depend on the brand but mostly 2010 onwards have this fuel cut-off feature already ... doesn't matter what speed you are in ... you release accelerator pedal while vehicle is in gear and in motion, the fuel supply is cut-off ...

**12vdc** · June 25th, 2018 11:30 AM

Originally Posted by Walter

That's why I indicated modern vehicles with modern engine designs ... as to what year that is would depend on the brand but mostly 2010 onwards have this fuel cut-off feature already ... doesn't matter what speed you are in ... you release accelerator pedal while vehicle is in gear and in motion, the fuel supply is cut-off ...

If you cut-off fuel supply, the engine will die and is a very dangerous scenario at cruising speed.

**Walter** · June 26th, 2018 08:29 AM

When the transmission is still engaged – be it an automatic or a manual – the computer will detect acceleration without any throttle being applied, and it will cut fuel to the engine. Yes, the engine is still running but the drive line is turning it over as opposed to ignited air/fuel mixtures in the cylinders. If the car is taken out of gear, the computer will detect there’s no throttle input or gear engagement, and as such will supply enough fuel to the engine so it will idle.

Do You Use Less Fuel Coasting In Gear, Or Shifting To Neutral?

Myth-Busting: Coasting in neutral can save you fuel? | Practical Motoring

**kisshmet** · June 26th, 2018 11:35 AM

Originally Posted by Walter

That's why I indicated modern vehicles with modern engine designs ... as to what year that is would depend on the brand but mostly 2010 onwards have this fuel cut-off feature already ... doesn't matter what speed you are in ... you release accelerator pedal while vehicle is in gear and in motion, the fuel supply is cut-off ...

The system control the amount of fuel fed into the engine

Cutting off fuel is like turning off the engine

Even at neutral the system controls fuel supply to the engine to keep the engine running at 700-800 rpm. More fuel is fed to accelerate, reduced when decelerating.

On automatic systems an excessive engine shudder (sign of stalling) is sensed and more fuel is automaticaly supplied to keep the engine running smoothly even if the foot of the driver is lifted from the accelerator

Gasoline engine need both fuel and electricity to keep running

Diesel engine need electricity only to start, after that, only fuel feed will keep the engine running

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