My freind used his mustang gt 2011 to jump start my friends 06 (approx.) GMC Yukon

Everything went fine at first as we were able to start the yukon

But now my freind (mustang) says his battery is messed up, he says the volts are dropping?? and that it needs to be replaced.

Is this possible, we did need to leave the cars connected about 20min before the yukon started.

Thanks

 

If anything, it may have affected your friends alternator. The alternators and OE batteries in the S197's are marginal and it doesn't take much to degrade the alternator. Have it load tested.

 

Isn't that why you always rev your engine a bit when trying to jump another car? I always assumed doing that would put way less strain on the alternator/battery than just letting it idle...

 

At idle, the alternator's output is a good bit lower than it's rated output. I haven't seen output curves for our alternators but those that I have tend to peak at about 1500-2000 RPM, IIRC, and maintain that output relatively flat with higher revs. But idling the car being used to charge the dead car simply results in the charging vehicles battery supplying more load to the dead car. But considering our alternators being rather fragile IMO, it probably wasn't the best thing for it.

 

Did you simply leave the mustang connected to the Yukon without maintaining a 2000+ RPM in the Stang to actually charge the Yukon Battery?

If you didn't then you could have fried the battery in the STang. Automotive batteries do not do well when their voltage drops below a certain level. At idle the car barely puts out enough to charge one battery let alone a second one.

Leaving the car idle would also explain why it took 20 minutes to get the Yukon to start. A minute or two at 2000+ RPM should do it. If not, time to call it quits and just get another battery for the vehicle needing a jump because it is TOAST anyways.

 

Battery =s bucket
Alternator =s pump

Yukons bucket needed to be filled before trying to jump start it.
Might have killed the stangs marginal pump.

 

this is why i don't jump other peoples cars.

 

Tell me about it, I don't know if you remember but I posted a thread about my check charging system indicator and heat. Well, turns out my alternator was dead, I pulled into my mechanic's garage and my car just shut off. Spent $400 for everything, but I got a lifetime warrranty on the alternator.

 

The wrath o the masses will smite thee if you do not update that thread.

I was wondering what you actually did ultimately.

 

Amen to that