Of "high performance engines" and jump-starting cars

[Una_Persson]

@Q.E.D.

I’m thinking stress on the vanes. Is it possible for these to break or deform under sufficient fluid stress?

I’ve seen people do the most absolutely horrendous things to automatics (shifting into honest to goodness 1st at 90mph, shifting into reverse at 60 and actually having it try to do it, putting it into Park at near triple-digit speeds, bunny hopping until the bellhousing cracked into tiny pieces, an ATF line wedged up into the flexplate and sawed through at speed…) and it seems more likely that the transmission or driveshafts would give first. But anything’s possible…

[Rick]

@Finagle

Well, there might be something to it, although the fault doesn’t seem to be so much “high performance” as that the BMW electrical system seems unable to cope with potential high voltages.

From here :Tip #3: Due to the varying nature of car electrical systems, never jump start your BMW using another car that is running. Use the other vehicle’s battery power alone to start it because a 14.5 volt running system (i.e., GM) can seriously damage a 12.6 volt system (i.e., BMW) due to the overvoltage.
To me, that sounds like bad engineering, as most cars will be called upon to perform a jump start at some point in their lives.

I’m with Gary T on this one. Lots of half truths, and semi misinformation on that page. I would need to see a more authoritative cite about BMW electrical systems before I would believe that you cannot jump-start a BMW off a Chevy.

[RadioWave]

I’ve got the same engine (5 series) and not only can you jump start another car, it has metal tabs added specifically to help in jump starting other cars (The battery in many BMW’s is in the trunk for weight distribution reasons). I found the following information in my owner’s manual.

@BMW Owner's Manual

When your battery is discharged you can use two jumper cables to start your vehicle with power from the battery in a second vehicle. You can also use the same method to help start another vehicle.Use only jumper cables with fully-insulated clamp
handles.

[danceswithcats]

@Gary T

I’m not an automatic transmission specialist, so I don’t know the details. I doubt it would stress the torque converter, because I can’t think of how there could be damage in a fluid drive coupling. I did start my '64 Galaxie with a C4 automatic once by rolling it down a hill.

I had two different Mercedes sedans-a 1962 220 SEb and a 1963 300 SE, both automatics, and the owners manuals described the procedure to roll start. It only took about 5-10 MPH and when you slid into drive, they would turn and start.