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Overheating coil?
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local2Ed
Posted 2018-09-24 8:36 PM (#570723)
Subject: Overheating coil?


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1958 Dodge Coronet, 6cyl., automatic.

I was having a intermittent no-start problem that I believe I traced to the coil. It was an AutoLite coil that may or may not been original but it was the old style.
One of the other problems I was having was when warn, there was an irregular miss at idle That I could see in the engine movement and hear in the exhaust.
The car does not have a ballast resistor on the coil I replaced and don't believe one is called for.
Anyway, I put a new Intermotor, part # E40 ( supposed to be a BWD) coil that says "external resistor not needed"

The car starts fine and when I took it for a drive the miss at idle seemed to be gone. I drove it for a while and got home and left it idling in the driveway, the miss had returned and the coil was very hot to the touch just like the coil I had replaced. The coil is mounted on the side of the cylinder head on the 6 cyl. so I don't know if the coil is overheating from heat transfer from the engine or from over-voltage.

I am measuring full battery voltage to the coil, 12v to 14v depending on rpm's.
I've had this car for 5~6 years and don't remember if the original coil always was hot but it was in the car when I bought it and it never gave me a problem before and when removed there was no markings about using an external resistor with it and one doesn't show up in the wiring diagrams.

Would putting a ballast resistor on the new coil help if it is over-voltage causing it to become hot?
With the new parts today being what they are I don't know if I should trust the "external resistor not needed" on the coil.
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56D500boy
Posted 2018-09-24 8:45 PM (#570724 - in reply to #570723)
Subject: RE: Overheating coil?



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Location: Lower Mainland BC
Not sure if these diagrams help or not but they do show that the 6 cylinder didn't call for a ballast resistor. That said, it sounds like your coil *IS* getting too much voltage.

1956 Dodge:



1957 Dodge (I don't have one for a 58):





(57Dodge6CylinderIgnitionWiringDiagram.jpg)



Attachments
----------------
Attachments 57Dodge6CylinderIgnitionWiringDiagram.jpg (114KB - 13 downloads)
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Shep
Posted 2018-09-24 8:56 PM (#570728 - in reply to #570723)
Subject: Re: Overheating coil?



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Location: Chestertown, NY ( near Lake George)
Ive never seen a 12 v point ignition without some sort of resistor to drop the coil input voltage to maybe 7v in the run position, this will save the points. Coils normally get fairly warm. Some resistors are in the wiring, inline or internally resisted in the coil. Don't think this is your root problem. You could find out what the primary resistance is listed as for that coil and check it with a ohmmeter.
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local2Ed
Posted 2018-09-25 12:31 PM (#570750 - in reply to #570723)
Subject: RE: Overheating coil?


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Coil is working properly, battery voltage in, about 5.9v out to distributor so it is stepping down the volts correctly.
The temperature of the coil was 180* while the head it is mounted to was running 200*

I forgot that with this carburetor that is on there I could not get the pedal to go as far as the carb linkage toward idle. I have my idle set to spec when you let off the gas peddle but if you're under the hood and you push the linkage toward idle it will idle lower than spec and stumble.

I know the original coil was giving me trouble because when stopped at a light it would stumble/miss and more recently sometimes die out.
That is no longer the case.

Thanks for the reply's.
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Powerflite
Posted 2018-09-25 6:17 PM (#570770 - in reply to #570723)
Subject: RE: Overheating coil?



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Location: So. California
Yes, the original coil you had, should have been about 0.5 ohm primary resistance and would require an external ballast to work. I am amazed that it worked as long as it did though. When I ran an original coil on my V8 without an external ballast, it shut off the motor within 5-10 minutes of driving. Dead, nothing until it cooled down enough to work again. So you probably had a higher primary resistance version than that.

Your "no external ballast required" coil has some resistance built into it. Here's the rub. 4cyl motors require 3 ohms primary resistance, 8 cylinders require 1.5 ohms, and 6 cylinders require.....you guessed it, 2.2 ohms. So my guess is that you have a coil made for an 8 cylinder with no ballast, and it is working on your 6 cylinder, but is *marginal*. You could add an extra .5 to .7 ohm external resistor to it to make it work better, mount the coil on your fender or firewall to allow it to heat sink better, or get a coil made for a 6 cylinder motor with the proper external ballast. An E-core coil is not subject to heating issues like the canister type coil is, so a higher (1.5 ohm or more) primary resistance version that won't burn up your points is another option. A coil made for a 4 cylinder will work too, but won't provide as much power. In fact, it may be true that there isn't a 6 cylinder version with internal resistance available because the factory just adjusted the external ballast to make it work well. Aftermarket companies came up with these internal ballast coils, and they may not have expected to sell any to 6 cylinder motors with points. So I suspect that if you ask at the counter what you should use, they will likely sell you one made for a 4 cylinder motor with 3 ohms resistance.

I hope this helps.
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local2Ed
Posted 2018-09-26 8:22 AM (#570780 - in reply to #570723)
Subject: RE: Overheating coil?


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There are different numbers for 6cyl. coil and 8cyl. coil. I have the 6cyl. number. This application uses a internal resistor coil I suppose because there is full battery voltage from the original wire leading to the coil and about 1/2 that voltage going to the distributor when hot. I haven't checked the voltage to distributor when cold but I am interested to see what it is. I may do that this morning.

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