coasting vs in gear

[thro]

heh. I coasted down greenmount in the 180 with the wolf, in gear, engine running with the fuel cut active and it dropped about 20-30c in engine temp by the bottom of the hill

[JAFA]

carbourettors in cars return unburned fuel to the tank. carbys on bikes do not.

Really?? 'Cos all the old cars I've ever owned, and still own, have never had fuel returns back to the tank. Some of them have an overflow hose that drains out onto the road, just like my bikes, the others have nothing, just rely on the float needle and seat doing it's job.

Back on topic, driven wheels / tyres have less friction than undriven ones, so if you can work out how much the friction increases when you coast in neutral, it may or may not negate the petrol saving by being at idle. There's a challenge for ya!!

[JAFA]

At the risk of sounding racist - when I was a kid my Dad (in NZ) used to coast downhill all the time to save petrol in his old manual Morris Oxford. He called it "Maori Overdrive".

Haha bro, long time since I've heard that one!! My cars all have that feature too

[ripper1199]

...have never had fuel returns back to the tank....

Usually it is a valve ("idle shut off") operated by vacuum that shuts off air or fuel (depending on carb) in the low idle system. High rpm, foot off the accelarator creates strong vacuum, valve is actuated and no low idle mixture goes in the engine. No fuel consumption. Engine rpm drops far enough or you put foot on pedal vacuum is not strong enough to actuate valve against spring no more and she burns fuel again. Only the second to last (lot of vacuum lines) and last generation (even some electric shit) carbs had that in the late 70ies and ongoing in german cars as far as I am aware.It was then that they started with economy and catalytic converters. The same valve can also be electrically actuated and is then sometimes only used to shut her off and protect the catalytic converter so there is no " run on". But even these days it is common with bikes. My Honda 2009 bike has one of these valves (little diaphragm actuating a little pin on the side of the carb). Hence no cool explosions out of the muffler unless you go to a whole lot of trouble.

[Akzle]

You'll also have to use alot more brake to manage your speed if you coast vs stay in gear as you'll have no engine braking.. So save a few cents but wear out your pads/rotors faster......

brake pads are cheaper than engines ><

Usually it is a valve ("idle shut off") operated by vacuum that shuts off air or fuel (depending on carb) in the low idle system. High rpm, foot off the accelarator creates strong vacuum, valve is actuated and no low idle mixture goes in the engine. No fuel consumption. Engine rpm drops far enough or you put foot on pedal vacuum is not strong enough to actuate valve against spring no more and she burns fuel again. Only the second to last (lot of vacuum lines) and last generation (even some electric shit) carbs had that in the late 70ies and ongoing in german cars as far as I am aware.It was then that they started with economy and catalytic converters. The same valve can also be electrically actuated and is then sometimes only used to shut her off and protect the catalytic converter so there is no " run on". But even these days it is common with bikes. My Honda 2009 bike has one of these valves (little diaphragm actuating a little pin on the side of the carb). Hence no cool explosions out of the muffler unless you go to a whole lot of trouble.

^^what this guy said.

[Cosimo_Zaretti]

When I was 17 I used to turn the engine off on the MK1 Cortina and coast home so my parents wouldn't know how late I was after boning the girlfriend in the Lake Monger car park. When I upgraded to a HQ Monaro disaster almost ensued because of the steering lock.

The "oh shit the steering lock's still on" moment. I remember my dad turning up to tow my first car up a hill, and he was pretty pissed off about having to come and get me, so he took off before I'd been able to release the steering lock. Tow cable snaps taut and I'm headed for the kerb cos I can't correct, I can't remember if I braked but the tow bracket resolved the situation by sheering at the welds and was catapaulted skyward with some force. We never found it the bracket.

[CT90]

The most I have got from keeping my speed down and coasting down hills after the fuel light has come on is 68 k's. I think the least I have got from doing the opposite is about 30k's or less.