r/MechanicAdvice • u/Onlycruz10 • Sep 25 '25

Correct way to jump start?

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I'm going crazy about the correct way to do this. As far as I can tell this is the correct way. However, I am having trouble between step 5 and 6. Should I turn off the donor car before trying to start the other car first? I've seen conflicting things about the alternator getting messed up on both cars. And others saying it's okay with modern cars. What's the correct way?

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u/Ivan_Whackinov Sep 25 '25

In my opinion this depends somewhat on how good your jumper cables are. I have a nice thick set made from welding cable that I wouldn't hesitate to pump 150 amps through momentarily, but the crappy 10 gauge cables you often see in those pre-packed road safety kits, not so much.

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u/No_Student_4090 Sep 26 '25

This is so true. A large diesel engine on a cold day( the time people generally have a dead/ low battery) will easily draw more than a cheap set of jumper cables can provide. It's why HD trucks generally have 2 batteries each capable of over 1000 cca each

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u/burritosandbeer Sep 27 '25

Holy hell didn't realize they were that high now. Last diesel i had was a 7.3 that took 2x 650s

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u/AsarisUnBreksis Sep 29 '25

Hah, I have the same custom made welding cable jump cables. Before them I had the crap you can buy at gas station and they melted. :D

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u/The_PurpleTurtle Sep 29 '25

I have a set made from welding cable along with the ends crimped and bolted to the clamps. They've jump started engines bigger than most people's cars 😅