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Old 05-08-2014, 09:39 AM   #1 (permalink)
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Question Coasting: in gear vs. neutral

Hi,

I was driving a friend's Renault Scenic which has an onboard fuel computer and was surprised to see that when coasting downhill while still in gear (foot off accelerator), the current fuel usage was 0.0ℓ/100 km.

Do cars use less fuel when coasting in gear versus when in neutral? Or does it depend on the vehicle?

I've always coasted down hills in neutral (idle), thinking it was more economical.

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Old 05-08-2014, 10:41 AM   #2 (permalink)
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Even though the engine uses no fuel when coasting in gear, the engine drag slows you down and shortens your coast so quickly that you get better overall fuel economy by coasting in neutral even though the engine is running since you are coasting so much further when in neutral. Of course the best fuel economy can be gotten by engine off coasting in neutral. Coasting in gear has a place in FE driving, mainly for limiting speed on steep down hills, when coming up to a place you have to stop, or for reducing your speed when you are getting too close to the car ahead of you.
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Old 05-08-2014, 11:08 AM   #3 (permalink)
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Ah right, this makes sense.

So even though no fuel is used when coasting in gear, the distance gained by coasting in neutral off sets the fuel that is burnt when idling down the hill?

I drive a 2006 VW Polo which has power steering, I don't think it'll be happy coasting with the engine off.

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Old 05-08-2014, 11:15 AM   #4 (permalink)
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Old 05-08-2014, 11:16 AM   #5 (permalink)
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Quote:
Originally Posted by Bataleon View Post
So even though no fuel is used when coasting in gear, the distance gained by coasting in neutral off sets the fuel that is burnt when idling down the hill?

Unless it's a steep downhill, there's a limit to even how far you can run with the engine drag. Get a long hill in neutral and you go forever.

Best of all is EOC, of course, allied to skillful clutch starting to save wear on the starter motor.
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Old 05-08-2014, 11:32 AM   #6 (permalink)
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How I find it :
If you are on a very long hill using a kill switch or turning off the ignition is useful while in neutral. I have a hill that I coast for 10km on that I use my kill switch on but not for the 200ft long coast as it passes so quickly that little to no gain can be realized.
In short its a lot of work for a little gain. Most small cars use about 1/3 gal. per hour at idle so that much is possible to be saved with continual obsessive engine off in Neutral coasting.
Using a kill switch(or turning off the key) is a distraction that best left for those purposely long coasts in my opinion.
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Old 05-08-2014, 05:37 PM   #7 (permalink)
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Coasting in neutral is only effective in carburettor-fed engines, or in Diesels with all-mechanical injection. But it still wouldn't worth the increased wear on brake pads...
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Old 05-08-2014, 06:31 PM   #8 (permalink)
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Quote:
Originally Posted by cRiPpLe_rOoStEr View Post
Coasting in neutral is only effective in carburettor-fed engines, or in Diesels with all-mechanical injection. But it still wouldn't worth the increased wear on brake pads...
Not sure why you say that...? Coasting in neutral is effective on any vehicle when the conditions call for it... If one needs to use brakes when coasting in neutral, then it's not being done right.
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Old 05-08-2014, 07:21 PM   #9 (permalink)
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That's probably the best guide. If you need to use the brakes, you ought to be coasting in-gear.
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Old 05-08-2014, 08:43 PM   #10 (permalink)
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I coast around in neutral every chance I get , it and low rpm shifting are my favorite and most effective Eco-driving tricks that I employ.

I agree that if you need to hammer on your bakes you should not have chosen neutral at that time or place.
Some trial and errors may be needed but it is easy to master, you can shift between 5th and neutral in order to control your speed..

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