1984 BMW 325 Ignition Coil Exploded

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JASONBERG
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My 1984 325E BMW wasn't starting. I tried all the basic tricks to get it going, jumping it, ensuring snug connections on all wires, making sure the battery was fully charged. After some investigating, I believed the problem was with my Ignition coil, so I replaced that. The battery was weak, so I used a portable jumping battery to try to get the car started. The engine cranked, but wouldn't turn over. So figuring this problem was beyond my skills, I had it taken to the local repair shop. The next day they called me to inform me that my ignition coil had exploded. I went up there, and to my chagrin, it had. There was black goo all over the engine and on the windshield. They claimed that they had only charged the battery and tried to jump it. I have my doubts, cause that's exactly what I had done to it. Anybody know what would cause an ignition coil to explode?
Apr 22, 2006 at 4:20 AM
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LOSONE
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Very typical older model Bosch coil--I have seen them explode on older models with the old style Bosch coil. Kind of reminds me when I have had too much iced tea!
Apr 22, 2006 at 11:56 AM
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JASONBERG
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Glad to hear this isn't a complete anamoly, but could you explain why this occurs? Did it receive a surge, or could it be a human error caused this?[/quote]
May 5, 2006 at 9:56 AM
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LOSONE
  • ✓Experienced Mechanic
  • 1,616 POSTS
The compound they use in the oil Bosch coils and many other brands break down with heat over a period of time. The high voltage , 40-50,000 volts shorts to the insulation and the coil explodes.
May 5, 2006 at 10:06 AM

Suggested Repair

Replace the ruptured oil-filled ignition coil with a suitable replacement. On older Bosch coils, the internal compound can break down from heat so high voltage shorts through the insulation and ruptures the coil; have the ignition and charging circuits checked rather than assuming a jump start caused it.

Conversation Summary

The owner of a 1984 BMW 325E had a no-start, replaced the ignition coil, and later learned the coil had exploded and sprayed residue over the engine. The owner asked whether a voltage surge or jump-start error caused it. The expert said this is typical of older oil-filled Bosch coils: the compound breaks down with heat over time, and 40,000 to 50,000 volts can short through the insulation and explode the coil.

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