There was a VERY important line in my list Steve - 'I open the boot and uncover the battery for a few minutes'. Hydrogen floats on air and very quickly disperses. You would not however do it if the battery was inside the car where the roof will keep the gas trapped.

Secondly, all the talk about destroying the car's electronics is obviously wrong. I've misconnected it (by mistake), and the car suffered no damage at all. Nor did the donor car (another Jag). The radio failure is a mystery, but in reality probably isn't related.

I often wonder how many 'facts' are stated as fact when in reality they are just over-cautious statements originally made by manufacturers to protect their backsides in any eventuality. Now, if you have actually destroyed your cars electronics by incorrect connection ........... !

 

The tales of disaster usually stem from someone connecting the jump leads to the battery connections in reverse, maybe you dodged a bullet by going to the fuse box.
Perhaps you would be willing to run a test?

 

There's no doubt that this and many other recommended procedures consist of 'best practices' and may in reality only eliminate a tiny element of potential damage.

The correct way of doing it takes no more time or effort than other methods- so why not use it?

 

Simple reason Mikey - I had no idea that my Jags had a procedure for jumpstarting. I did it the same way as I've done since the 70's. Cars have changed of course, but batteries more so. We no longer have the open vented screw cap type - they are all semi-sealed now.

There are a couple of other points - a battery only gives off hydrogen whilst 'working' or charging. A 'flat' battery shouldn't be doing anything.

Then there is the difference between adding a further battery (in parallel for jumpstarting) and switching something on - such as the starter. Both induce spikes. In fact, every time a relay operates in the car there will be a spike of some kind. How come an 'added battery' spike is any different to a relay? Then there's the hard reset situation - no power at all and suddenly the (fully charged) battery is reconnected.

I can understand someone blowing up a battery if not careful, but I am still not convinced that adding a jump battery damages any electrical circuit.

Forget my reverse connection error - that was stupid beyond belief - but the important thing is that even that didn't destroy the car's electrics.

We need someone with a burnt out car (and a red face) to put his hand up!

 

The recommended sequence for connecting/disconnecting cables has been around for decades. Nothing new or different with it being a Jag.

The only different thing I see is not having the donor car running. I'd always kept it running out of ignorance, but now wonder what benefit that had. Given that an alternator can put system voltage at over 15vdc, perhaps Jag has a concern that this is an unnecessarily high level during a simple jump start and that straight battery voltage of 12.3ish vdc is sufficient.

 

Well - as they say - you live and learn. Hopefully I won't need to jumpstart again so it won't arise. If it does I will try it without running the donor car or perhaps disconnect the earth and let the donor charge the flat battery for 10 mins.

 

I agree with that some guys are saying here, most printed circuits and elec components on PC's, laptops, mobiles have built in surge protection, it doesn't take much to put it on. No idea why car components don't have this.

 

They do, but the spikes can be huge. More importantly the currents etc are a severe fire risk if people make a mess of jump starting - as they do!!

 

Hmm, but the surge protector power pack I got says it can protect against lightning strikes, can't be much more powerful than that surely the battery could be connected to something similar, before it delivers power to any component.

 

Or just make things simple and follow Jag's 'best practice' instructions?

 

Well I don't know about that Mikey. Out of ignorance (of an official Jaguar procedure) I have always jumpstarted my cars in the same way with no ill effects. And Jag's definitive statement that disconnecting the donor car with the engine running WILL damage the electronics just isn't correct. And if that bit is rubbish ................... !

 

My car has been jump started once by a breakdown company with no bad effect either. Though don't know what would happen doing it multiple times over a set number of days.

 

I see all this talk about Jump starting a Jag, So I went to the owners manual to see what the Manufacture says. Here I is what is says when using a jump star vehicle. "2. Do not run the engine of the jump start vehicle when boost starting a Jaguar vehicle. if the jump start vehicle's engine is running and the jump leads are disconnected, damage to the Jaguar vehicle's electrical system will result. It then says to attach positive to positive first, then negative to the earth stud on the left-hand side of the spare wheel well. It does say in bold Caution: Do not connect the negative jump lead directly to the negative terminal of the discharged vehicle.

My point here is read the owners manual first to be sure.

 

You are quite correct Luke (RTFM as they say!) The trouble is ..... it's rubbish! I, and several others, have broken all the rules jumpstarting our cars, and no-one seems to have destroyed their electronics.

I suspect that the procedure was written in the early days of ECU's etc and no-one was too sure about spikes and disconnections.

 

Most amazing to me is the resistance to just doing it the way Jag suggests. It's no more work or more complicated than any other method and in fact simpler than some of the ideas put forward.

The only 'change' I've made to my own procedure is not running the engine on the donor car. I'll save a fortune in gas..............

 

You've hit the point there Mikey - now that I (we) know we may well 'follow the rules'. All I am saying is that out of ignorance I (we) have been doing it the old way and it's not caused any problems.

 

It's akin to people saying "I get static electricity shocks (from crappy carpets or whatever) and have never damaged my computer". Some can genuinely say that. But some would say "yeah, me, too, till last week and now my computer's dead".

It's the same with jumpstarting. Chances are you'll not be unlucky but I don't get why people would rather take a chance when there's no need to.

 

Sort of like playing Russian Roulette with Dirty Harry's 44 Mag for a week, but never landing on the live cylinder, huh?

That day will come........

 

Theres a risk with everything in cars and life, what people are saying is WHAT is the risk vs reward, what value will I get for that risk of damaging the car.

You could change an alloy wheel and damage the tyre valve in the process, is this going to stop people changing wheels?

I doubt we can get percentage/ratios of how many people have jump started vs how many people have damaged their elec components, but from what people are saying and my experience, it looks very unlikely.

 

Good Question. Thanks for the feedback. Great Post.