Coasting vs engine braking

I hired a scooter whilst in turkey recently for a little trip along some coastal roads and it was a 2 stroke.

At some points down very long downhill sections I would have been off the throttle for maybe a couple of minutes and technically 'coasting'? But there is no neutral gear because it was just a 'pull and go' type affair of course.

Would I have been damaging the engine? It did cut out the once because I was going downhill for so long and had to stop and restart it :D

Though I don't think it was holding any revs when off throttle so may not have been engine braking. I don't know enough about bikes/scooters/2 strokes to know what is and isn't normal anyway.
 
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Devrij said:
Forgive me for this, but I thought I would venture in here for once to ask this question that's been playing on my mind.

My commute involves driving up one set of hills and then down the other side (with an epic canyon run). That means half of my 45 min journey is downhill, and in rush hour it's usually slower than or at the speed limit. Because I use a fair amount of fuel in the twisties and on the big straight at the top, I try to economise on the boring bits by putting my car in neutral and just using brakes for the second half of the journey.

My assumption being that the engine is still drawing fuel through at a higher rate when engine braking at 2-3k rpm than it is idling at 900rpm. Over the course of 20mins or more every day, do you think there is any significant saving even if it's a quid or two per week? Or is my understanding of idle jets and such flawed?
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If it is a modern car you will be better off ( and safer) just leaving it in gear down the hill. I have a similar part of my journey to you go down it in gear.
 
Any car with a real time fuel usage monitor will show you that it uses no fuel in engine braking situations and some (although very little) while idling. How modern is the car?
 
From looking at instantaneous fuel consumption on petrol cars with trip computers, they often burn some fuel when engine braking during warm up. Once the car's warmed up, they cut off fuel completely during engine braking.

So apart from the first mile or so, you can generally assume that fuel cutoff will happen.

However, saving fuel isn't just down to the cutoff. You can sometimes save more fuel overall by building up more speed on a downhill section and using the extra momentum to carry you some distance.

On hypermiling forums they tend to advocate things like the Forced Auto Stop (FAS) where you coast with the engine off for minimum resistance and maximising the use of momentum. I regard that as pretty dangerous though - not advisable and of dubious legality.
 
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Clarkey said:
Never understood that, can someone explain how the car is any less under control when out of gear? The way I see it, a car is fundamentally more stable without drive forces acting on one of the axles. Even if you disagree, how is it any different to driving an automatic trans, are they all dangerous?
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I guess there's a few factors:

1. Potentially reduced braking force - doesn't really matter anymore as cars can easily brake harder than the tyres can handle in normal conditions, though you are putting unnecessary heat in to the brakes that could cause fade.

2. You can't quickly accelerate - having to go back in to gear to speed up, and possibly having a problem there, creates an unnecessary delay should you need to speed up for some reason

3. The car behaves in a way that's different to normal and so may surprise you

4. An undiscovered engine fault could result in a stall (e.g. some engines with certain sensors that are playing up randomly die at idle) - this won't happen if the wheels are turning it

It's nothing really major, but people get hung up on these things.
 
Modern engines use no fuel when coasting in gear (assuming fuel injection and manual gearbox). The injectors will kick in again somewhere around 1500rpm, so ensure you're coasting in a low enough gear to keep the revs reasonably high (but not too high, or you'll get too much engine braking effect).
 
that thing about the 1400-1500rpm point where the injectors start again is spot on correct.

for additional fuel economy im surprised they dont extend that down to 1200rpm or so
 
My 107 cuts the fuel if you let go of the accelerator above 1600rpm, doesnt kick back in if you go below that though oddly. With 2nd redlining at around 65mph its the perfect gear for those gradual downhills!
 
Django x2 said:
it saddens me that a lot of MPG gauges show OMG 99.999mpg when coasting in neutral :(
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It has to stop somewhere I guess. My 2010 Honda Insight shows a bar graph that maxes out at 100 mpg. It has a separate screen that shows when genuine fuel cut is occurring (but it won't show both at the same time). Alternatively you can change it to metric units and get 0.0 l/100km.

I preferred my old Fabia's "----" on the mpg readout when fuel cut kicked in.
 
When people refer to engine braking, do they mean sequential shifting to brake or the brakes and just the gear that they happen to be in at the time?
 
Burnsy2023 said:
When people refer to engine braking, do they mean sequential shifting to brake or the brakes and just the gear that they happen to be in at the time?
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In this case rolling down hill in a gear that offers resistance to maintain desired speed without throttle (with some brake dabbing).

I thought everyone did this? It was certainly the way I was taught. I also enjoy wailing down a motorway slip sans breaking and going 5th - 3rd - 2nd.. then whatever is needed at the end. Probably not advised I guess :confused:
 
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