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Discussion Starter · #1 ·
Two questions Im hopeful someone here can answer.

2006 2.0L Diesel, 4WD Kia Sportage XS

Does free wheeling (out of gear) down hills save fuel ?

Does anyone know the most fuel efficient speeds in 5th and 6th gears ?
 

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Free wheeling out of gear is not a safe way to drive - suppose you need to accelerate to avoid trouble - but in anycase your fuel consumption drops markedly when in the descent even in gear.

The general advice with diesels is to change up at 2000 RPM for fuel efficiency - this would give you a 'top speed' of 60 MPH if you stuck to 2000 RPM in 6th - aerodynamics means that fuel consumption climbs rapidly as speed increases so driving between 50 & 60 MPH will help your figures. Once the engine is warm and provided you are not going up hill or head on to a hurricane, you should be able to drive in 6th around 50 - 55 MPH and with the torque of the CRDi 1800 RPM is a practical cruising engine speed.

There may be some Diesel Particulate Filter issues if you don't allow the engine to warm-up thoroughly but a 10 mile run at 55 MPH should be adequate in my experience with the Sportage.

Richard
 

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Hi StnDuck,Agree entirely with thunderbird. Coasting in neutral uses MORE fuel. I saw your post this morning and checked my theory whilst out.
According to my scanguage, coasting down a hill in neutral showed about 234mpg, but in drive and foot off throttle it showed 9999mpg (no fuel used).
Its a similar arguement to keeping an auto in "drive" at the lights - mine uses 0.31 galls per hour but if in neutral with brake on shows 0.11 GPH.

OH - thunderbirds safety comments are spot on!
 

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a modern engine uses NO fuel when off the throttle BUT only when in gear. Since the advent of dual mass flywheels and direct injection the ECU (cars brain) only injects fuel then there is a request from the throttle peddle for torque. The road wheels divert power back through the drive train to maintain engine rotation but without the need to burn fuel. This wasnt possiable years ago because oil pumps/water pumps and gearboxes couldnt be all controlled individualy as they can be nowadays. If you free wheel the ECU realises to maintain engine rotation and operation it needsinjects fuel to keep the engine going, or otherwise known as idling.




As for the most fuel efficent speeds, they "should" be at the peak torque point of the rev range but without a power curve chart i cant tell you.Although there are so many variables its hard to just say....."stick to Xmph and you'll save loads of fuel"



traveling up a hill for instance...sticking to 1800rpm where theres lots of torque and letting the engine struggle will use alot more than 2800rpm and using the momentum. As a good guide you want to be as low reving as possable without the engine understress.
Edited by: RichieD76
 

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Discussion Starter · #5 ·
My humble thanks to all who have responded. I guess a drive to driving patterns is now justified for myself !
 

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I once had a mate who had a Opel manta and he used to free wheel all the time ??? until when he needed to put it back into gear??
doing 50mph freewheeling and put it into first gear by mistake!!!!!! lets just say the car had to be scrapped as he shatterd the gearbox and drive shafts.

i have the 6 speed 4WD 06 plate and found it a great drive in 6th at 60mph getting good MPG



Lance
 
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