Why don't people just bump start? You only need enough charge in the battery to excite the alternator field coils-and that's b***** all. I've never liked jump leads-far too much sparking for a 12V device imo!

They just say that to stop people spinning an ailing engine in the hope that it can be forced to start. Bumping is for flat batteries. If it doesn't start during cranking, it is time to start fault finding.

Bumping actually dumps far less fuel into the exhaust because the ECU massively over enriches when the engine is being cranked on the starter.

And the cat doesn't work for about 30 seconds after a cold start, so it couldn't overheat the cat anyway!

When I was really into hypermiling. I always switched off the engine and restarted wherever possible by bumping. Hundreds of bumps later and the cat is fine. The same cannot be said for the torsion springs in the clutch assembly though-which is the only reason I stopped doing it.

Edited by unthrottled on 14/10/2012 at 19:44

This is true! But you can you can often find an obliging passer-by if you haven't got any friends :)

It is amazing how much harder it is to push a cold car than a warm one.

A good friend had a Modus, a terribly built car, difficult to work on BUT great visability.

2 hours to change a head bulb, near impossible to work on the engine without removing lots of stuff and poor build quality all round.

I think it was born during the bad days of renault between 2001 - 2007.

Well, I agree about the headlights (although I learned a short cut which meant I coud change bulbs in 20 minutes tops) but in the 8 years we had one it worked very well and gave us very little to complain about.

I know absolutely nothing about modern cars and their electronics etc. What I can remember from years ago is messing about with a twelve volt wiper motor whilst it was turned on (intermittent). As it 'parked' I must have been touching a live contact, because I got quite a strong electric shock. (Voltage spike ?) No further damage was done, but I suppose the same fiddling about with a new car might result in a serious damage, and with a ten year old - maybe a write off. What I mean to say is that the several thousand volts needed to 'shock' me must have passed through the battery via the earth, and anything connected to the battery must have - bla bla bla.

Electric motors (and other devices with coils) generate a back EMF when the circuit is broken. 12 volts to a wiper motor can momentarily give maybe 120 volts - quite enough to give you a jolt.

Hi. You posted a few years back that you had found a 20 minute shortcut to changing the headlamp bulbs on Renault Modus.

I would really apreciate it if you could share the shortcut with me, as I am a Modus owner and spent 2 hours last time round!

Thanks!

Bump starting is fine... If you are facing down a decent hill or have a handful of people to push you.

.........not if it's automatic gearbox. Bring back the starting handle, as on our old Rover 105S [the poor man's Bentley, for you younger readers!]

I agree with Simons comments.

There is always a risk with jump starting a car and certain precautionary steps should be taken.

If the battery is totally flat ( which if the ign lights were on then it wasnt in this case ) its always best to remove the keys from the car and out of range ( some cars when the keys in range the ECUs become live )

Very good advice about taking the key fob out of the activation range of the vehicle for keyless-starting vehicles, leaving a few minutes for the various ECUs to sleep is a good idea too. Perhaps we should start a line of Faraday cages for workshop use!

To go back to the OP:

If the immobiliser light was flashing, what was the point of trying to jump start the car anyway? That seems like a pretty basic error to me.

As I wasn't there I can only assume that the lack of starter motor activity caused her to think that the battery might have lost power (enough to power a small led but not enough to turn the starter).

Indeed. What I was trying to say was 'why did the rescue service person not realise that an active immobiliser meant there was no point in trying to start the car - it would have been better to try to reset the immobiliser'.

Can't answer that one. It seems obvious with the benefit of hindsight but in the heat of the moment......

This thread has been resurrected because Vwerner wants to know from csgmart how to change is lightbulb!

Edited by Brit_in_Germany on 13/05/2016 at 13:43