Hi,

Just for future reference, is it safe to jump start a V6, or use it as power source to jump start another car? I've read somewhere that some modern computer controled engine managment systems can be terminally buggered by load fluctuations caused by jump starting unless the leads are fitted with some kind of buffer. My car has an automatic gearbox; will this be damaged if it's towed any distance in neutral? Finally, most auto boxes will not take roll starting (freewheeling down a hill in neutral then engaging a low gear to turn the engine over). Is this the case with the box Citroen used on the V6? Again, I've heard that some auto boxes will allow this without being damaged.

Still not got the starter motor off, one of the ramps started to bend when the car was on it and I've not replaced it yet. Still not read most of Norrie's XM cd yet, so I don't know the best route through an incredibly crowded engine bay to get to it. Probably find it's got some bizare sized Torex bolts holding it in...............

Regards,

Jim.

Jim,

To answer your queries in the order asked:

There should be no problem jump starting either way. The electronics are pretty robust. I have never believed previous stories which abound about this. Obviously if you have a dead short, say, in the car which won't start and you connect the good car to the other with jump leads then you may cause damage to the battery or alternator of the good car. But then this is common sense.

Don't know about autoboxes to answer your question fully. I would suspect towing in neutral would be fine since no work is being done by the box. If the fluid inside churns during this process I'm not sure if the heat produced would be dissipated by the oil cooler. Maybe the oil wouldn't be pumped in the right direction? Someone who knows auto boxes would be more qualified to answer.

cheers

noz

Thanks Noz,

I've found the starter motor, it's hidden behind a metal shield that looks at first examination to be part of the gearbox cowling. Must get awfully hot in there, which could indicate where the starter problems lie, and yes, it is just behind and above the flow distributer and its tangle of hydraulic pipework, all of which look like they need to come out to get at the thing. Obviuse route in seems to be take the front of the car off, take out the radiator (maybe find duff wiring for cooling fans), then it looks like there's enough room to work. Alternate could be to take everything off from underneath, but this looks awkward.

One question; how do I get the front valance off? (the painted panel that goes across the front of the car, just below the bonnet) With the three top screws off it's loose, but seems to be fastened to the front inner edge of the front wings. There's a small pop out cover inside the wheel arch in front of the wheel, maybe there's some kind of special tool needed to poke in here ans loosen something off.

Thanks for your help Noz, your cd is excellent but will take a serious weekends browsing.

Jim.

Jim,

Ther are another couple of screws hidden behind the grille where the chevrons are. Get a torch and you'll be able to see them.

Hope the CD helps you to solve the problem.

Cheers

noz

the reason that you can get problem with jumpstarting is that when you initialy start, you have got 24v instead of 12v.this can sometimes blow your alternator or cause a problem with other electrics. thankfully this is rare as most items are fairly robust, however it has happened to me on 4 occasions.

sorry to disagree mach11 but you're reasoning is wrong. You could only get 24v if you connect the batteries in series. This would mean disconnecting one of the battery terminals, linking + to - from one battery to another and finally the spare terminal linked back to the one you disconnected. All in all not an easy job.

If you connect the batteries in parallel ie +ve to +ve and -ve to -ve then you'll still have 12v, maybe a lot of additional power but still only 12v. If you connect an infinite number of batteries in parallel you'd have infinite power but still only 12v.

This is not what causes electrical failure when jump starting cars. It's usually connecting the jump leads the wrong way round or earthing a stray +ve lead against the engine or body.

cheers

noz 8)

Hi Noz,

What you say about series and parrallel wiring is 100% accurate, but are there circumstances where breaking or making a circuit can cause a temporary voltage spike, or rise? If this is so, then could a voltage spike be caused at the moment you make the connections coupling a second battery in parrallel with the first?

Just a thought, late on a Wednesday night..........

Regards,

Jim.

Hi Jim -

For voltage spikes (overvoltage surges) to occur when making/breaking live connections, you must have some inductance (i.e. coiled circuit) in the circuits.

The lenght of the jump wires does in fact cause a minor inductance, but this is so small compared to the very low (ohmic) resistance of the battery cells. In the event the dead car's battery is defective, and hence would have a high internal resistance, you won't get a current surge which would cause a voltage spike anyway.

I think the worst you can do is to directly connect jump start cables on to the startermotor terminals, as the startermotor is a huge inductance in itself.

Another cause of voltage spikes, is the sudden load seen by the helping car's alternator, which will be exposed to a sudden minute voltage drop by the load connecting a dead car's battery. The effect is then the alternator will kick back with a minute overvoltage, trying to immediately compensate the sudden voltage drop.

It's all marginals, since the alternator have a finite reaction time to alter it's charge voltage, and I believe that most fatal events is caused by rescue car drivers connecting directly to startermotor on dead cars.

These modern "electronic" jump start cables contains a lump where a couple of surge arrestors are fitted, exactly to shortcircuit (or limit) voltage spikes. Some cheaper variants simply have coils and a small capacitor, which are not that efficient.

I have never heard of or experienced any events with broken down electronics by jumpstarting a dead car. Only read of it all over.

Hi Anders,

Fair points all of them. A lot of these stories gather speed in the telling; everyone `knows' this happens even though no one (or at least very few people) have first hand experience of a jump start damaging anything. I think the problem is compounded by their being so much electronic `stuff' on modern cars. Just as Doctors tend to say `it's a virus' when they mean `I don't know', so a lot of auto technicians (car mechanics in the old days) will blame a faulty module, then lighten your wallet by a few hundred quid to replace the thing..........

Cheers,

Jim.