Loose starter connection

[80stech]

I know this has been covered before but I just wanted to post a refresher on this. I have been experiencing just the odd time that my starter seemed to lag a bit. I checked the connection nut yesterday and sure enough it was quite loose. Hopefully that was the problem and I seem to have caught it before too much melting or heat induced corrosion has happened. Kinda the same deal with the power distribution box connections but those I tightened as soon as I saw the box was made of plastic. Anyway, just a heads up reminder. Cheers
Also I should add a safety reminder... that connection goes straight to the battery.

[NotAnyoneYouKnow]

I seem to get that lag every so often. I'll take a look. Thanks for the heads up.

[andrewwynn]

Doesn't take much of a bad connection to make a big difference.

The starter pulls 200A. That means every 0.005 Ω resistance will be a loss of a volt.

Considering the contacts on a switch are typically at least that much or double that a loose terminal ring could easily be 0.1 Ω. 0.1 Ω times 200A would be 20V loss starting at 12 it's pretty clear that would be enough to inhibit a start.

If just a little loose and 0.02 Ω:

That means 4v lost on the connector and only 8v left to start.

Also 4v x 200a is 800w which will melt things very quickly

One last example: just a tiny bit loose: 0.01 Ω: that means 2v loss and 400w on the connection.

I had a loose nut on my alternator once and it actually fell off. When I stopped to investigate why my car was giving me odd gremlins I looked down in the engine bay and it was self-coreect illuminated from the alternator bolt GLOWING!

(It's an eight mm nut in case anybody else needs to replace it)

[80stech]

Yes, I wasn't expecting this as much on the starter because the solenoid cap back in my day was usually bakelite, but I guess maybe now it is plastic! It was one of the earlier threads where the guy found this to be the problem that got me thinking!

[80stech]

Now that I think of it this might be why on some rebuilts they leave the first nut just snug. Oh crap, I used to always tighten that up which makes the problem worse when the cap shrinks!

[80stech]

Haha, kinda funny BMW (more us i guess) is probably a victim of thier own German bred OCD just like me!