Ignition coil overheating?

[dorsett5965]

Hello again,
Took the boat out on the river today for a couple of hours and it stalled when brought down to neutral.
And would not fire again
After digging around for a half hour, I noticed the coil was burning hot.
I cooled it down in a bucket of ice and was able to get started, and ran back to the marina.
anyway, last year my tach or wireing shorted out my dist coil and I disconnected the tach wire. Just two days ago, I found that replacing the wire to the tach brought things back to normal ( so I thought)
So would anyone know if I have a bad tach or bad coil or bad wireing that would cause my coil to heat up to the point of not functioning ?
1965 mercruiser (150) 230ci chevy IL6.
tha is, Jim

 

[achris]

Check the coil is getting reduced voltage, not full power. With the points closed, measure the voltage at the coil positive... Should be around 7 volts. If it's close to battery voltage (12v), then the resistance wire has been removed from circuit...

Chris........

 

[dorsett5965]

Great thanks,
I will check today. I only have one wire to the coil and two on the dist side (one being tach)
so assuming the resistor is inline somewhere before the coil ?
I will get back with readings.
thanks again,
Jim

 

[dorsett5965]

Hi,
points closed 10.55
points open 11.99
with tach wire removed.
also does the case of the coil need to be grounded?
clamp is loose and the threaded set screw that would only push on the coil is missing.
and also in this 5 minute test reading, my coil was heating up ? No running or cranking of the motor.
thanks, Jim

 

[Bt Doctur]

Being that old it may have had a white ceramic ballast resistor , no actual resistance wire . If the voltage is not what is specified get a dual ballast resistor for a Chrysler auto using points ignition

 

[dorsett5965]

Great,
I assume I need to locate that ceramic resistor, get it out of the line and put the new resistor In line ?
BTW I have been running this boat (1965 Dorsett ElRey) for 5 years now so this is something that just has happened Maybe added load of tach ?
thanks again I will replace the resistor and get back.
probably in a week.
Jim

 

[Bt Doctur]

start by measuring the voltage first, you may have a alt issue

 

[dorsett5965]

Ok,
So I should run the motor and then read the voltage coming into the coil while the motor is running?
Will it be fluctuating with the points opening and closing ?
Or should I be reading the altinator output while charging?
Thanks

 

[dorsett5965]

Hi,
Would my coil be getting hot just with ignition key on (in run) without engine running if it was an alt problem ? And cold (off for 12 hrs+)
The coil was getting hot just testing voltage at coil without starting engine.
Thanks

 

[achris]

If the points are closed, then power is running through the coil. Yes it will get hot.

 

[dorsett5965]

Thanks, Chris.
So heating up is normal ?
I was wondering if that would eliminate the alt question that Boat Dr. had, if alt was not running.
What did you think about my readings at the coil?
Thank You for being patient !
Jim

 

[achris]

I think, I agree with bt. Your resistance wire is not a resistance wire anymore. The fact that you only have one wire on coil positive is another clue.. Should be 2, one is the resistance wire the other is the feed from the starter motor (to give the coil full power during cranking )... Once you reinstate the resistance, you're going to need to also reinstate that wire too.

 

[dorsett5965]

Great info thanks,
I have been running this boat for 5 years and not messed with the coil wires except last year taking off the tach wire from the neg (dist) side of the coil.
Is that possible ? Or I will dig up the picture I took before I removed the tach wire it's always possible I am not remembering what I took off. And maybe short runs with the boat since then did not heat up the coil to malfunctioning.
Thanks you all for your valuable experience.
Jim

 

[achris]

Just looked in the manual at the wiring diagrams. It looks like I'm going to have to take back all I said.. There is no resistance wire on the diagram for your engine. It's straight 12 to the coil... ok, that said. You'll need to check the coil. It will need to be 3Ω not 1.5Ω (as is a coil used with a ballast resistor). If it's 1.5Ω, that will explain it getting too hot.. And as there's no ballast resistor, that's no cranking bypass wire form the starter motor. One wire on the coil is correct....

Very sorry for the misunderstanding. Don't see many engines this old these days..

Here's the engine wiring diagram for you if you don't have it...



Chris.......

 

[dorsett5965]

Hi,
I only have two wires coming to my coil, one yellow from the ignition switch and one brown from the tach. Which is how it's been since I started running this boat years ago. I have taken off the tach wire which leaves only the yellow wire. The yellow wire from the ignition switch passes through the shift control, which is the only part of the wire I have not visually seen (inside the control box)
I did not locate any resistor ceramic or inline.
the only other wire at the coil is from the -side to the dist.
I will try reading through my selog manual, but often times I don't find what I need for this 1965 mercruiser.
Thanks again Jim

 

[dorsett5965]

Looks like we sent posts together.
Thank you for the diagram so much !
I will check the coil.
Thanks again, really appreciate you guys sticking with it and digging up info for me!
Jim

 

[dorsett5965]

Also, no need to apologize, I'm the one with a boat older than myself.
And I might need to apologize, I'm thinking that when my tach wire shorted out my coil last year, In my trouble shooting mistakes, I did swap out the coil with one off my 59 ElCamino.
maybe I left it in the boat ? It is a coil needing an exterior resistor.
I will look at both coils tomorrow and see what I did.
Looks like it's the bottom of the 9th at any rate.
Thanks, Jim

 

[achris]

..I will try reading through my selog manual, ....

Let's see if we can get you a proper manual, not a knee rest....

... It is a coil needing an exterior resistor....

"External resistor required"

Putting full 12v on that coil will definitely overheat it....

Chris............

 

[dorsett5965]

That would be very helpfull.
I did buy on ebay a couple years ago 4 or 5 used shop mercruiser (in thick binder form) manuals to cover the year of this boat. Obviously I need to sort through them.
BTW, I did put the coil back in the truck last year, so the coil in the boat is the one I got it with. And the more I think of it, I have on occasion had hard starts after running. But usually I am running to fish and spending hours on an electric motor. My coil would probably cool down before start again.
Things are adding up !
Thanks again and let me know when you have time what's available in manuals.
thanks, Jim

 

[achris]

That would be very helpfull.
I did buy on ebay a couple years ago 4 or 5 used shop mercruiser (in thick binder form) manuals to cover the year of this boat. Obviously I need to sort through them.
BTW, I did put the coil back in the truck last year, so the coil in the boat is the one I got it with. And the more I think of it, I have on occasion had hard starts after running. But usually I am running to fish and spending hours on an electric motor. My coil would probably cool down before start again.
Things are adding up !
Thanks again and let me know when you have time what's available in manuals.
thanks, Jim

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