Ground for Jump Start

[ATF]

Hopefully I'll never need to jump start my car, but in the event that I do need to, where is a good source for a ground under the hood? Ideally the engine block/valve cover, but I don't really see a good place to connect the clip. I did a couple of searches on here and bf.c but didn't pull up anything that helped.

[lazoh]

Originally Posted by ATF

Hopefully I'll never need to jump start my car, but in the event that I do need to, where is a good source for a ground under the hood? Ideally the engine block/valve cover, but I don't really see a good place to connect the clip. I did a couple of searches on here and bf.c but didn't pull up anything that helped.

I've personally have used the strut bolts (that is if you do not have a strut bar). Hope this helps.

[zboot]

frame of the car

[aceyx]

At the front of the motor is a loop used to hoist the engine out. I've always used that.

[m3outtanowhere]

i have used all those places. pretty much any large metal surface will do

[mohaughn]

You also know not to jump an older BMW with an american or even a newer BMW? The voltage is slightly different. Our cars run right at 12.2 or so volts. A lot of other cars run at 13.6 or so. They are all considered 12 volt systems but I have heard of people frying electronics in BMWs with the output from an alternator on a different kind of car. If anything, just connect the batteries and then try to start it with the other car not running. I usually try to avoid jump starting a car at all costs.

[pdxmotorhead]

All lead acid "12" volt batteries produce 13.2 volts when fully charged and in good shape.

The older BMW's that got fried were the ones that had two batteries,
they had the normal one in the trunk, and a second "system" battery
under the hood that was for maintaining the ECU when off. Folks would try and jump them and blow the ECU cause the car would try and jump through the alternator wiring and toast the ECU(s) the 7 Series were the usual victims of this....

I believe it was the V12's that got the worst rep due to the multiple computers all of which cost like 4 K each ANd they were difficult ot diagnose as to which unit was really dead.


Dave

[mohaughn]

That could be the case, but I know my e39 produces 13.4 volts off of the alternator when the car is running. Both of my e36s only produce something like 12.2volts off of the alternator.

That is why I recommend jumping with just the battery, don't start the 2nd car as the voltage running through the car when the alternator is providing power is different.

I have seen a few posts over at bfc where people had problems with either the ASC control unit or DME after jump starting the car. I guess it is possible that they did something else wrong but I've always played it safe and try not to jump start my e36s off of a running car.

[aceyx]

Battery to battery is a recipe for disaster (AKA lead-acid explosion).

If you're playing it safe, run the positive off the alternator lead, which will run it through the voltage regulator. Ground is as normal.

In any event, follow the instructions in the owner's manual.

[pdxmotorhead]

So I disagree...

If you crank the starter with the Plus/Red cable from the jumper set connected to the alternator lead you'll likely melt the wire to the battery, that wire on my car is only like 10 gage (IE 1/8 in diameter) Where the battery cables are 1/0 or so to carry the 300 amps the starter can pull during starting. 10ga is good for like 30A continuous.

Proper connections for jumping a car are:
Connect positive to battery terminal on both cars, connect negative on the car with the good battery to good engine ground NOT the chassis,, . Last connection should be the negative/black cable to the engine ground on the dead car.

The only reasons a battery explodes are: Excessive hydrogen gas from being over charged or just used hard, or if the battery has an internal short which causes extreme heat, boils the battery inside and ignites the above mentioned hydrogen.
Yes you should always be careful jump starting a car, best is to use an old beach towel to cover the battery area when your jump starting to catch the shrapnel if it pops.

BTW I used to jump 20 to 30 cars a day as a parking lot guard in college I never had a jump done as described fail or cause damage.

Dave