[ssf556]

Are you guys dis-engaging cruise control when going down a hill? And then re-engaging cruise control at the bottom.

I have noticed that this does significantly increase fuel economy. I guess a form of hyper mileage.

I know there is similar technology in some of the Freightliner trucks that will allow the truck to go to neutral and idle when going down a hill. Their system is more advanced than what I am doing, because it is based on actual GPS location and terrain.

Thoughts!

[thelifeofmikeyy]

Although I rarely road trip my F30, there is one instance where I did this exact thing. I was on my way back to Southern California from Phoenix and while descending from Chiriaco Summit into the Coachella Valley, I disengaged cruise while remaining in ECO-Plus and coasted at 75MPH downhill for roughly 10 miles. It was fantastic!

[lpaulodt]

I do it all the time. I always try to maximize efficiency using the topology when cruising. It also keeps me entertained on boring trips 😄

[Eddamoo]

Yeah i do in situations where i don't need the engine braking. Our G02 X4 does this in Cruise Control so BMW added it as a feature after our cars.

If you set cruise to 65, it auto engages coast mode and allows the car to coast to ~61 and 69mph respectively before accelerating or re-engaging the gear.

[Eaglesview]

Going downhill in cruise the system will apply rear brakes to maintain selected speed. At 92,000 miles on original brake pads.

[ssf556]

Originally Posted by Eaglesview

Going downhill in cruise the system will apply rear brakes to maintain selected speed. At 92,000 miles on original brake pads.

Understood and that is generally how all CC systems works.

Trying disengaging cruise control going down the hill and then reengaging cruise control when you get to the bottom.

The key is to drop the rpms to idle. That helps with FE.

[Eaglesview]

I have been under the impression that when a diesel engine is being driven by the inertia of the vehicle such as decelerating off the accelerator the fuel input is completely cut off.

[Enabled]

Originally Posted by Eaglesview

I have been under the impression that when a diesel engine is being driven by the inertia of the vehicle such as decelerating off the accelerator the fuel input is completely cut off.

This is true, but the engine braking will slow you down faster than if simply coasting while idling with very very little fuel. There is a point where the car will travel much longer and use less fuel overall than engine braking and then having to reaccelerate again. It all depends on the driving situation.

[Eaglesview]

Agree, it does depend on the driving situation. On my X3 the advantage of keeping the engine engages is further battery charging recovery as indicated on the dash by a blue bar. I have read the battery regulator only allows the alternator to charge the battery to 80% full charge.

All being said, very trivial advantage no matter the choice.

[Onizukachan]

Originally Posted by ssf556

Are you guys dis-engaging cruise control when going down a hill? And then re-engaging cruise control at the bottom.

I have noticed that this does significantly increase fuel economy. I guess a form of hyper mileage.

I know there is similar technology in some of the Freightliner trucks that will allow the truck to go to neutral and idle when going down a hill. Their system is more advanced than what I am doing, because it is based on actual GPS location and terrain.

Thoughts!

because of the active braking cruise, You don’t get the benefit of coasting/ sailing if cruise is on even if in eco pro. In hilly terrain or going over the mountain I don’t use cruise instead letting it overspeed by 3-5 downhill and under speed by 2-3 near top of the hill.

[Billfitz]

Originally Posted by Eaglesview

I have been under the impression that when a diesel engine is being driven by the inertia of the vehicle such as decelerating off the accelerator the fuel input is completely cut off.

It's cut off with diesel or gas, so engine braking doesn't cost you fuel economy by using gas. It costs you fuel economy by not letting gravity increase your speed going down hill via free-wheeling. If you're in Eco Pro the car will freewheel downhill if it's in D and you don't pressure either the gas or brake pedal. But if you're using cruise control that will apply the brakes going down hill, so to free-wheel you have to turn the cruise off. The easiest way to do that it to lightly tap the brake. When you get to the bottom of the hill and slow back down to the set cruise speed push the resume button.