Fuel consumption problems

[Craiglxviii]

Or to noise. But some of that helps with coping with the day ahead eh?

 

[JBell]

ANY cruise which maintains a constant speed MUST use energy faster than a skilled driver will manually. This is because cruise will always try to maintain a speed. That means (as Ian and I pointed out) a wider throttle opening going up hill and slowing down (using engine braking - aka pumping losses - or brakes) to control speed going down hill. That slowing down will not be making use of the energy consumed going uphill, whilst a constant throttle opening does (when it can be maintained). Even putting the car in neutral and allowing the potential energy (altitude) to be converted to kinetic energy (speed) as the sole motive force will give better results than automated cruise control. An internal combustion engine is around (lets be generous) 40% efficient. The chemical energy used going up a hill is therefore always going to be greater than the recovered energy downhill. If you allow the vehicle to accelerate down the previous hill on the approach to the next hill then you are exchanging some of that potential energy gained by altitude (and the consumption of chemical energy) into kinetic energy (speed) as opposed to losing it to heat (engine pumping losses/braking). Energy lost to heat does not help our fuel economy.

I always turn the Cruise off when going down hill

 

[Submariner1]

Funny how much prejudice there is against Lexus. Our LS400 was a brilliant car, even at 14 years old.

I have 3 friends who were all long term repeat MB owners, they moved from big Mercedes to big Lexus’s.

Only fault amongst the 3 Lexus cars (over circa 4 years) was one had a slight squeak, just before the passenger door fully opened. (fixed in 15mins whilst he waited ... plus 20 mins for them to wash his car as a courtesy).

They all admit they are not as pretty or as “loveable” as their previous S and SLs, but way, way better built!
Neither will ever return to Mercedes ... ABC and electronic problems!

As one summed it up. With a big Mercedes if you have 9 months trouble free motoring you feel lucky. With a Lexus it doesnt even enter your head that it will break!

 

[John Laidlaw]

It’s a simple summary really:-
Lexus- disengaged and in pocket
Mercedes- engaged and out of pocket....
Simples!

 

[Taffy7hfa]

Surely an idling engine will always return zero mpg ? I don't understand how idling can be turned into an mpg figure.
If you have a diesel leak you can usually smell it before you can see it, even a small leak will cause a strong smell either outside or inside the car.

 

[LostKiwi]

Surely an idling engine will always return zero mpg ? I don't understand how idling can be turned into an mpg figure.
If you have a diesel leak you can usually smell it before you can see it, even a small leak will cause a strong smell either outside or inside the car.

It'll return 0mpg as long as it's not coasting down the road in neutral..

 

[Taffy7hfa]

Used to do that a lot with my old V8 Landy, not recommended with an auto box though !

 

[BClassChris]

Used to do that a lot with my old V8 Landy, not recommended with an auto box though !

Agreed though modern auto boxes now have the intelligence to recognise when they need to coast and when they shouldn’t - hence the development of eco roll


Sent from my iPhone using Tapatalk

Available at: https://zeppelinit.com

Hope you have a great day

 

[LostKiwi]

Used to do that a lot with my old V8 Landy, not recommended with an auto box though !

It's very much dependent on the box. 722.3 it's a no-no but 722.6 it's not an issue.

 

[Paul Goff]

It's very much dependent on the box. 722.3 it's a no-no but 722.6 it's not an issue.

Could you elaborate a little, Kiwi? My car has the 5 speed 722.6 box and I have been an inveterate coaster in neutral for many years! But that was in manual cars, having had a secondhand gearbox and new electroplate fitted recently I am keen not to rock the boat if there is the slightest chance of doing any damage if I coast in the car. So I have not been doing so since I got it.

 

[BClassChris]

Yeah please elaborate as when I’m coming up to lights or a junction and I ease off in enough time I can actually feel the gearbox drop out of gear and roll forward under its own steam so to speak


Sent from my iPhone using Tapatalk

Available at: https://zeppelinit.com

Hope you have a great day

 

[LostKiwi]

Could you elaborate a little, Kiwi? My car has the 5 speed 722.6 box and I have been an inveterate coaster in neutral for many years! But that was in manual cars, having had a secondhand gearbox and new electroplate fitted recently I am keen not to rock the boat if there is the slightest chance of doing any damage if I coast in the car. So I have not been doing so since I got it.

Sure.

The 722.6 has speed sensors internal to the box so knows which gear it should be in when coming back out of 'N'. The electronics will use this information and select the correct gear accordingly.
The oil pump is driven at crankshaft speeds so even in neutral will maintain pressure (there are actually several pressures present in the 722.6 - there is main pressure which is pump output, working pressure which is used to operate valves under solenoid control and lubrication pressure. All of these are present at all times as long as the engine is running.
In terms of the clutches even when in gear some clutches and bands are not engaged and are designed to cope with this. Same goes for bearings and sprag clutches.

Older gearboxes use differential oil pressure (no electronics) to control gear selection and these can get 'upset' and 'confused' if you go from D to neutral and back on the move. The older 722.3 gearbox is a good example of this.

Some older gearboxes have pumps in the output shaft (Borg Warner 35 is an example) which take things one step further and allow not only running in neutral but also allow for roll starting of the car. For older gearboxes it is very much a case of how the box is designed.

 

[BClassChris]

Ah right ok that would explain then why my car when I let it drop out of gear rolling up to lights (whilst still in D) then put my foot back on the gas if they change in the mean time it doesn’t throw a barney. Would I be right their LostKiwi?


Sent from my iPhone using Tapatalk

Available at: https://zeppelinit.com

Hope you have a great day

 

[LostKiwi]

Ah right ok that would explain then why my car when I let it drop out of gear rolling up to lights (whilst still in D) then put my foot back on the gas if they change in the mean time it doesn’t throw a barney. Would I be right their LostKiwi?


Sent from my iPhone using Tapatalk

Available at: https://zeppelinit.com

Hope you have a great day

No idea as I'm not familiar with your gearbox.

 

[BClassChris]

No idea as I'm not familiar with your gearbox.

Fair enough

Not too sure what box is in it just know it’s a pita when it’s cold though


Sent from my iPhone using Tapatalk

Available at: https://zeppelinit.com

Hope you have a great day

 

[LostKiwi]

Fair enough

Not too sure what box is in it just know it’s a pita when it’s cold though


Sent from my iPhone using Tapatalk

Available at: https://zeppelinit.com

Hope you have a great day

I think pre-2011 it will be a CVT so totally different to a traditional automatic gearbox.
Post 2011 it will be a 7 speed DCT (again very different to the traditional automatic) or a CVT.

 

[BClassChris]

Pre 2011 it’s a 2009 CVT


Sent from my iPhone using Tapatalk

Available at: https://zeppelinit.com

Hope you have a great day