Hello! Just discovered your channel. I live in the US (California) and have a 1993 850Ci that I love, 3rd owner, 135K miles, had it since 2007 and, as my mechanic says, I will be buried in it - not due to accident but because I will never let it go. I knew that jumping was a bad idea, but since mine is currently dead due to being out of town and not driving it and so happy I saw your video. I will invest in 2 new batteries to be safe. An aside, I watched your vid of getting your car back after accident and you mentioned the headliner sagging. I just got mine done at my local BMW specialist (Coast Motor Werk) and it looks amazing - they did an ultrasuede that matches my gray interior perfectly and apparently will "never" sag. They did an amazing job. I also had the bushings replaced since apparently my engine was resting on my exhaust system. Very different drive after, and I'm not sure I like it since I was not used to a bouncy ride. Mine is silver OG color that is super faded. I am considering Techno Violet (individual color) but love the Maura metallic that you have. Thank you for the videos and the detailed information.

Yes, well said again Timm, another informative video. Just for the sake of informing a lot of your fans commenting, I have several old cars, including the E31 that I try to keep going and batteries are a pain, as you have so perfectly explained on previous videos. I have, for a few years now, two main tools in my arsenal. One is a top quality "intelligent" battery charger (not too expensive really), and a new spare battery that I keep topped up fully charged. If there is no real alternative to jump starting the dead car, such as where it is parked, then jumping from a good battery rather than another car is much safer. Also switch the headlights on before connecting the jump leads, leave them on until you have disconnected the leads, this gives an extra load to absorb any spikes. Keep the vids coming!

My thoughts Tim, rather than opposing opinion as this video will help someone bricking a module which is unrecoverable. I'm using 35 years on the spanners with some electronic experience (to be completely transparent 20 years of that, was corporate IT and cars as a hobby) those connectors under the bonnet are for convenience (as stated by BMW) battery location which helps with the neutral front/rear balance can be a time consuming activity to access (model dependant). The problem is some of these cheaper jump starters is they have burst voltages way above 20 volts (non BMW alternators may have this issue, I can't say) which is enough to corrupt modules whereas most BMW alternators top out at 15 volts which is just within the safety threshold. To summarise briefly and reduce any possibility of module corruption (jumping BMW to BMW which I do for coding sometimes) I'd connect jump leads with the jump car engine off, then try to start the car with the flat battery. The extra 100 amps or so you'll get with the alternator running (assuming you have good jump leads capable of carrying 200amps minimum) isn't going to make a huge difference and most batteries sit between 12.5 to 13 volts which is well below the voltage required to corrupt module memory. Just my opinion only, pinch of salt and all that, keep up the good work! :D [edit never killed a module ever, done a few hundred at least]

I jumped started once my e39 from my battery another car, gladly nothing happened. Thanks for sharing this precious info!

Wow! I've been lucky so far with my E64 then! I've jumped started mine once and jump started another from it once. I won't be doing that again after your advice Timm. Thanks 👍

Your like tiff needel and James may in one. Thanks for learning me something today .

I blew my DME in my E64 after Jump starting it. I wish I knew this info before I jumped it. Thanks Timm.

As always, thanks for the education Tim.

BMW's are jump started in BMW workshops all over the world every day. In 40 years working on BMW's never once had an issue. With the 1 in 10 rule , I should have had about 200 problems. There is a problem with the maths somewhere .

Thats some solid intel. Well done.

Thank you Tim, valuable information ;)

'I'm a little bit weerrrr, a little bit weeeeeey, a little bit dodgy!'

What about using the newer lithium or super capacitor jumper packs ? Maybe you could do some testing for us plebs😉

I think the root cause of jump-starting problems (aside from reverse connection) actually comes from the fact the dead car's battery has sulphated of effectively has a high internal resistance. This means that when the car finally starts and the jump leads are disconnected there is not enough resistance in the battery to buffer the output of the alternator which can surge sky high. I good rule of thumb is if the battery can start the car then its probably safe to run the car. Therefore if the car needs to be jump-started then the battery is probably not good enough to safely run the car. One may think the battery will charge up quickly, this is not true on a battery that's been sitting for a long time. It may only take a few amps of current even at 50 volts so there is effectively nothing to clamp down the alternator voltage.

Interesting discussion. Older electronic components (ICs) can easily latch-up. When this happens they get very hot and will eventually destroy themselves or their power supply. A transient voltage or spark can do this.

Thanks for the very informative video - cheers -

Great information! I will definitely not be jumping my E39 after watching this. But what about a jump/starter pack? The sort the connect to the cars battery/jump points and then gets switched on? Do they create the same high voltage spike when there switched on aft connecting to the car? We use them alot at work on modern BMW/Mini Thanks

Thanks Timm.

Jump leads with surge protection are available which can manage the inductive effects. Better to avoid jump starting altogether, but there is a technical solution for this problem.

Just keep a small lithium jump pack in the boot. Check the charge level a few times during the year. In the winter whenever the temp drops to 0, I will hook up a trickle charger to my car battery for a day to keep it fully topped up. Those trickle chargers only put out about 1.5 amps max. So will not harm anything.

Jumped my 99’ e36 M3 a couple times, WITH NO PROBLEMS, at the battery terminal, before I finally replaced the dead battery.

Is there any difference when you connect and disconnect a battery?

Damn. I keep a pair of jumper in the trunk. Not the cheap crap with the sheet metal pliers, the real deal that pinch grown man style, made of plain thick metal. And I've jumped a few cars in desperate need of juice here and there. Now that I know, thanks to you Timm, that it can pop a random module of my e39, I'll keep them for my old Civic. She hopefully doesn't mind a few spikes of volts. Or perhaps it could damage the alternator' regulator ?

Good Advice

Timm thank you, also the problem is most Bmw owner is just do sth then invest is it right or not. Some of them dont know black, red polar. I saw important mistakes outside. Some Bmw services even dont know how to charge battery. In Turkey is it normal to service destroy your car easily.... 2 days before I cleaned all grounds, checked alternator and its diods, cleaned sockets and got new Varta battery to make all system brand new. I have also battery charger with 3 A to make my battery minimum 12.50 V. )

Do modern intelligent jump start systems such as the NOCO Boost models avoid the issues raised in this video?

Hi Tim you know how many thousands of pounds you have saved people? God bless you! I enjoy watching all your videos thanks again.

I own a E32 740IL 7 series, and my battery out, thanks to you're video I will not jump it, but charge it I will do, but I can only locate the positive under the hood and not the negative. Is there a specific bolt or knot that will suffice for ground coverage? Like one of the bolt/knots that are located right were the shock absorbent is

I'm an electronics engineer and I agree with this advice. I'd add that many jump leads are poor quality and can make a fairly ineffective connection. When you consider how much current is needed to run a starter motor and you look at the way many cheap leads connect it's amazing they work at all! If you're having trouble be sure to turn off lights, stereo, fan, etc. and try again with the minimum electrical load. I've seen it make the difference on a low battery.

How about charging your existing batteries? I noticed you have a charging lead only on the left battery?

My 2008 750li battery does not last long sitting. We drive about once or twice a month. And I need to charge it overnight before. If I try to Crank it over after about a week, it's so weak .I used to charge it from the back directly, then I watched a video saying it will fry the electrical/computer system. Now I charge and " jumpstart " from the front

Hay Timm this is Alvin, your number 1 fan. QUESTION: When I replace my crankcase vent valve, do I need to replace or clean my breather hoses?

My question is my classic E38 only gets driven a few times a month and the way I store it is disconnect the negative terminal at the battery, when I’m ready to take it out for a spin I just reconnect the negative terminal ( there’s always a little spark when touching the terminal with cable), then I have power and it starts. Am I taken a risk by doing this? Thanks in advance.

Does this still hold true for the more recent models, say the 2018 X3 M40i G01 B58 engine?

Does the same apply to an E39 530D ? some context. i jump started a friends car and the next day my battery was completely dead. i did jump start it a few times after but no matter how long i left the engine started i couldnt get the battery to start my engine from cold. side note- my boot/ trunk latch developed a fault around the same time (broken spring) so the light inside the boot wouldnt turn off so i figured thats what had drained my battery over some time. However, i changed the battery for a brand new one as well as getting a new latch fitted and all was fine until a couple weeks later. i did not drive it for between 24-48 hrs and the battery was flat again . dont understamd why its happened can anyone give me any suggestions?

Hello Timm question for you love your info, I’m at a dead end with my car I change the battery and rebuild starter it started 4 times and went beck to making a clicking sound and will not start it’s a E 38, please let know what I’m missing or what’s wrong thank I need your HELP THANK YOU

Why do BMW fit jump points under the Bonnet if its not advisable to utilise them ??

My jumper leads have inbuilt surge protection; are they safe to use?

Hi Timm this is Alvin, your # 1 fan. Thank you for is video. Very informative, I just want to keep my 645ci safe. Say safe. 😀

It is normal for n62 4.4 series 6 to have when i drive hard 103 grades water temperature? Thanks

I’m keeping battery maintainer connected on my E31 terminals, is it OK??

As long as you don't connect the cables backwards and key is out or switch is off, it's ok.

Then why is there jump leads if your not allowed to do it? The factory has them for a reason

Well... my 07 X5 just got a jump as it was the only way to get it off the highway

Your voice is amazing

So how do I get my car started

2012 BMW 750 i Xdrive

I have a BMW I’m going to buy a 6 series next year but all this can’t jump start them because of the electronics just goes to show how crap these cars actually are! BMWs look great so do mercs but we buy with our eyes and worry about power instead of thinking logically and thinking about the mpg and reliability and quality of the car

Oh no Timm! I jumped my 840 yesterday - it ran though and I drove it about 24miles without issue- do you think I’ve got away with it this time? Wont do it again though! Thanks for the tip👍😀

Hi Tim, kind of related but then again maybe not..... my e64 boot has stopped working and I can’t open it at all. It did this a couple of months ago and then over night started working again..... do you think this could be a fuse? The latch? The battery? Any help you could give would be great before I send it in to the mother ship to change me mega money.... Chris.

Hole in hood?

I should really replace my batteries...

Not good

What a useless rust bucket. Thanks for the warning, just another confirmation that only idiots waste their $ on them!