Does bump starting damage anything? (Car)

[EazyDuz]

My car fuel economy is piss poor at 35-40mpg.
There is an ongoing debate about which saves more fuel, coasting in neutral down a hill, or coasting in gear (in a modern car the fuel cuts off, using none supposedly).

Well i thought what about scrapping all that, and turning the ignition off down a hill, then, instead of wearing out the starter motor and drawing battery power, just whack it back in the appropriate gear to match your rolling speed and bump start it.

I was rolling with the engine off the other day in traffic, about 8mpg, then when i needed to, i put it in 2nd, and it cranked over and came back to life, seemed quite natural and undamaging...


Also in b4 safety nazi's, i only intend to do it when i deem it safe. Does it do any damage to the car?
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To shreds you say? Tss tss tss

[EazyDuz]

[Islander]

No, as long as you choose a gear appropriate for the road speed you're coasting at.

[carvell]

?! You're mental!

Anyway... I don't believe there is an ongoing debate about which saves more fuel, coasting or going down in gear.

Going down a hill in gear will use no fuel (on pretty much any fuel injected car in 10 years), coasting will use fuel to keep the engine idling.

With your engine off your brakes will lose a lot of their effectiveness, and you could accidently put your steering lock on. A bit of a bonkers idea in my opinion,
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Yamaha TDM 850

[EazyDuz]

[carvell]

If the car is in 5th then there will be almost no engine braking - your car will accelerate if going down a steep hill in 5th (I've managed this on the M5/A38 section of motorway), you'll find that there's no advantage to running it in neutral.

Give it a go!
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Yamaha TDM 850

[EazyDuz]

[Pete.]

Lose your power steering and brake servo to save a quid or two a month?
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[jimspeed]

what car? bumping them can damage the cambelt and cause timing chains to jump teeth both resulting in a lot more expense than you would ever save in fuel. imagine there's your cambelt say nearing the end of its due service life and suddenly its having to go from standstill to >2000rpm in milliseconds when you use the starter it spins the engine at >350rpm so relativly smooth transition to idle speeds.
most timing chain setups run a hydraulic tensioner which is tensioned by the oil pressure so again sudden high speeds from standstill can cause the chain to jump a tooth or 3.
some cars will also log a fault code to say the engine has started without the key being turned (older scoobs do this and will stick the MIL lamp on after a few goes).
basically no your not really going to save anything and the loss of power steering and servo brakes could be a deal breaker one day.
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Hyosung cruise 125(passed test on, sold) Kawasaki el 252 (better than expected but sold on) Kawasaki GPZ500S first "big"bike.(sold) ZZR600 E5..Z750 2007,ER5, currently on a 2008 Enfield bullet electra x and loving it..
,"Alpha-9: Is there any correlation between dyno rod and dyno kits?"

[Kickstart]

Hi

You might gain a bit more momentum coasting in neutral rather than top gear.

However engine off you loose power steering and ABS / brake servo, and if the key slips out likely land up with the steering lock coming on.

Bump starting will likely dump unburnt fuel down the exhaust, which the cat and lamba probe(s) won't appreciate.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[i.p.phrealy]

yep, unburnt fuel will get through and knacker your catalytic convertor and EGR sensor.
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it is impossible to lick your own elbow...
and if you just tried you need professional help.
Finally allowed a big bike 19/03/14!

[covent.gardens]

Most people who meet me think I'm as tight as arseholes and it's true, I don't like to waste money...
but even I draw the line and I would never consider doing that.
It's pretty stupid really, all that effort for a few pence, if you were that bothered you should've got a more economical car in the first place!

[Villers]

[Walloper]

Dump the car if you are not very good at it and buy a pedal bike.
There is nothing wrong with knocking it out of gear on the downhill it will not damage anything.


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W-ireless A-rtificial L-ifeform L-imited to O-bservation P-eacekeeping and E-fficient R-epair

[hellkat]

When I was 22 I used to have an old Austin Maxi that never started unless I parked it on a slope and rolled it down the hill.

But it always started once I did that.

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Not nearly as interesting in real life.

[Kickstart]

[colin1]

You can turn the ignition off, then turn the ignition back on without starting up the engine. This way you have working power steering and brakes. You can then restart the engine when you want with the starter motor, to avoid the problems someone outlined.

I think turning off the engine at traffic lights makes more sense than on downhills. Some cars do this automatically and start again when you press the accelerator.
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colin1 is officially faster than god

[Walloper]

[Villers]

[_Iain_]

Simple realy.

Use bike for MPG

Use car for warmth & comfort.

No need to fuck about & risk damaging anything
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Please be aware that the above post may be full of complete nonsense.
Riding: '07 KTM Duke II, Baotian BT49QT-20 Driving: '88 Volvo 340

[Shaft]

[ashwin2936]

be careful, i was in a car where the driver turned the ignition of while going down a hill, as a result of this the steering lock applied and the abs wasnt working, we skidded into the on coming traffic and were very lucky not to have an accident.
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yq50, nsr-125, bandit-600, cbr-600 f2, zx6r g2, cbr929

[daemonoid]

[el_oso]

[Kickstart]