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Coil gets hot
Posted by: vacman ()
Date: November 17, 2022 04:06AM

1964 convertible, 2 carbs, not turbo, the car runs great when it is cold, after it warms up, it runs rough and if you shut it off, it will not starter until it cools down. The coil was almost too hot to touch so I had it checked and replaced it. I still had the same problem. A few people suggested I install a ballast resistor to the coil so I did that. I’m still getting 12 volt to the coil so the ballast resistor didn’t change anything. I’m being told that after the car starts the voltage to the coil should be around 9 volts. Any other suggestions I should try? Thank you.

Re: Coil gets hot
Posted by: JimBrandberg ()
Date: November 17, 2022 04:58AM

I think the voltage reading at the coil + terminal changes as the points open and close.
Coils have different resistance values. I think between the resistor wire and the coil you should add up to about 3 ohms. For instance a 1.4 resistance wire and a 1.6 ohm coil are about right.
I've had run ins with coils too hot a few times. Once a new coil fixed it. Once I went round and round with Pertronix modules and coils the customer had in his stash.
Hopefully someone smarter than me will add more, I'm not exactly Mister Electrics.

Jim Brandberg
Isanti, MN

Re: Coil gets hot
Posted by: Lane66m ()
Date: November 17, 2022 06:20AM

Is coil still on engine above the open hole on cooling box? If it is, move it to the rear frame by the latch support beam.


Re: Coil gets hot
Posted by: junkman ()
Date: November 17, 2022 08:55AM

There are 2 small wires on the starter. One feeds 12 Volts to the coil when starting, and the other feeds 12 volts to the resistance wire in the starter wiring harness to the coil once the car is started and you release the ignition switch from the cranking position. Coming out the other end of the resistance wire should be about 6 volts. The coil starts the car at 12 volts and then runs on 6 volts at the coil. You should also check your points to see if they are burned, and possibly the condenser might also be going bad due to the constant over-current moving through the points. The condenser is to help keep the points from arcing.

Woodstock CT... Located on the Connecticut / Massachusetts border, approximately 6 miles from the center of Southbridge MA. About 45 minutes from Hartford CT. 1 1/2 hours West of Boston MA. Woodstock CT to Los Angeles CA 2,937.1 miles. 1 Mile as the crow flies to Big Bird's nest.

Re: Coil gets hot
Posted by: RexJohnson ()
Date: November 17, 2022 10:11AM

When it won't start hot what is missing? Does it have a good start or none at all. Is there fuel? It should be fairly easy to find what is missing when it won't start.

RJ tools

Re: Coil gets hot
Posted by: azdave ()
Date: November 17, 2022 11:16AM

JimBrandberg Wrote:
> I think the voltage reading at the coil + terminal changes as the points open and close.

It most certainly does because the reading you get there is very dependent upon if the feed wire is under a load or not.

Also note that when you measure the voltage at the coil +terminal while the engine is running, what you are actually reading is blend of the readings between the the highest reading (when the points are open) and the lowest reading (when the points first close). Some meters do better than others when reading quickly fluctuating DC voltages so don't be too concerned about seeing exact numbers when checking voltages there.

Dave W. / Gilbert Arizona
65 Corsa 140/4
66 Corsa 140/4
66 Corsa 140/4 w/factory A/C
66 Corsa 455 Toro V8
65 Monza Convertible 110/4
66 Monza Convertible 140/4 A/C
65 Monza 4DR 140/PG w/factory A/C
65 Monza 4DR EJ20T/5

Re: Coil gets hot
Posted by: keitho64 ()
Date: November 17, 2022 12:20PM

Here is a link to how I resolved the same issue. I installed an old Chrysler ballast resistor. I did this a long time ago and has worked like a charm.


Are you using the stock distributor and coil?

64 Monza Convert
00 911 C2
"Horizontally Opposed"
05 GTO 6-speed (Gotta have a V8)
Chicago Burbs; the Anti-Dragon... 11 turns in 318 miles

Re: Coil gets hot
Posted by: JimBrandberg ()
Date: November 19, 2022 07:10AM

I worked on a Rampside 110 where it would start cold fine and continue running but if you shut it off hot you would have to let it cool before it would start again.
I pulled the coil wire and put to ground to observe the spark when cold, drove it around some and then observed the spark again. It was visually weaker.
I changed the coil to a different used one and it was fine.

I worked on a 140 where it would not start even though it seemed to have spark although maybe faint. Changed the coil and it was the same. Changed the condenser and it was fine, started right up.

I went round and round with a 140 with a Pertronix 2. It was wired wrong but worked fine for years until it gave up the ghost on a trip several states away on the way home.

All these were jobs for someone else so I don't know anything about symptoms beforehand.

Jim Brandberg
Isanti, MN

Re: Coil gets hot
Posted by: vacman ()
Date: November 20, 2022 05:06AM

Thanks for all the responses, I’m still trying to figure it out,

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