Using my D2 to jump start another car

[Adrian E]

Hi all

Been asked to help a friend get a car running in the morning - it's been sat for nearly 2 months in their garage with a flat battery! It's a weedy little Rover so shouldn't be too tricky for my truck battery!

Are there any precautions aside from the usual of not allowing the cars to touch I should be aware of?

I presume I can plug the jump leads straight across from my battery in the boot to theirs without any risk of damage to the electrics on mine?

Can't recall seeing jump start points under the bonnet to use instead?

Cheers all

Adrian

[Nollywood]

I would be cautious using my car to jump-start another car, with a very dead battery. It's one hell of a load, there's the risk of damaging semiconductor components in your car, especially if you're using non surge-protected leads.

I paid dearly with my B6 A4 3,0 Quattro. I needed a new ECU and when that was fitted, it was discovered the instrument cluster had taken a hit as well.

An expensive lesson, one I have no desire to repeat.

[Singh]

Scary stuff, Nollywood. Hope it ain't to late for you to back out Adrian? I'll never jump start again.

[Dezzy]

I have had no issues when using my 8 for jumping and have done a few times now, that said i don't know of the condition of the batterys in the other cars.

The owners manual gives instructions on what terminal to connect to first and for the life of me can't remember, think it was positive first.

You're right Adrian there is no points under the bonnet that i'm aware of

[HPsauce]

I've done it without problems (from the battery in the boot), but I don't have the newer battery management stuff to worry about.
I think the basic rules are:
1. Cars don't touch
2. "donor" car should be running
3. connect +ve first

[Nollywood]

HP, I think you should add to the basics "jump leads must have built-in surge protection." Like the ones used by the AA and RAC.

It doesn't always cause a problem, but it does happen. A very dead battery ideally needs to be charged externally before attempting a jump start. It's like a massive short across your battery terminals otherwise. A car with an electrical short could have catastrophic impact upon the electrical system of the jumper car...

Adrian, I would be really cautious. 2 months is a long time for a car to be sitting with a flat battery. A flat battery can freeze in this weather, and any attempt to jump start such a car could have dire consequences. A frozen battery can burst (I remember the same happened many years ago, in my BMW 1602). Scary stuff. All that was left of my battery was just the base, still held by the clamp. I was splattered by the battery acid, luckily it was too weak to do more than sting a bit.

I have a healthy respect for lead acid batteries now.

[Nollywood]

Adrian, if you really can't get out of jump starting this car (I personally wouldn't) I would suggest, at the very least you connect your leads with your engine idling, and leave it in this state for at least 30 minutes to charge the dead battery.

This way, it will reduce the load on your electrical system when the other engine is cranked. It's really cold out there, and trying to jump start without at least getting some juice into the dead battery will draw a lot of current from your own battery, and place a hell of a load on your electrical system.

Good luck.

[HPsauce]

I have to confess I've never done it with a "really dead" battery, just a "clunker".
(I've always put long- unused ones on charge first)
And yes, batteries are much "weaker" at lower temperatures; it's -2C here at present.

[Adrian E]

Thanks folks - got to the car, which turned out to be a low miler MG ZR, and it appears an interior light was left on when it was last used hence why it was flat as you like. Got the leads on and left it for quite a while, then experimented with the ignition and the fuel pump primed with plenty of enthusiasm. Gave it another 20 minutes with mine idling and then upped the revs - it started 2nd turn of the key and purred away quite happily.

Left them to drive down to Halfords and get a new battery - although it was quite a funny thought that they were all going to have to get in via the drivers door as the passenger one and boot were both still deadlocked! So that's baby into baby seat, pushchair on back seat, and a climb across the seats for one adult lol

[HPsauce]

If it's anything like my father-in-laws old small Rover 400 (sold last year, he no longer drives) the drivers manual tells you how to resync the deadlocking after restoring battery power.
(had to do it a fair few times in the past, takes only seconds)