66 c10 with a 250ci and bone stock quit on me the other day after about 20 miles, just like somebody shut the key off as it was going down the road. Had lots of fuel. After it sat for a couple hours it fired right up and worked perfect again. Will a faulty coil do that when hot?
Absolutely they can, although they are more likely to misfire a bit first. A bad condenser can also cause similar issues.
A likely reason relates to the fact that copper's resistance increases about 0.4% per degree Celsius. Taking into account that the coil's interior will be significantly hotter than the outer housing, the temperature could increase the coil's resistance to rise 60% -100 %. One can see that the resistance could easily be nearly double, reducing the coil's primary current by nearly half, resulting in an identical reduction in stored magnetic field in the core. An ignition system belongs to the "flyback" family of DC voltage conversion circuits. This coil does not act like a true transformer. Current flowing in the primary (when the points are closed) causes energy, in the form of a magnetic field, to build up in the core. When the points open and the primary current is suddenly cut off, the magnetic field starts to collapse, "dumping" its energy into the secondary. If the primary current were reduced nearly by half, the result would be a much lower amount of magnetic energy stored in the core, and a weakened spark; perhaps too weak to reliably start the engine.
My 59 Healey 100 6 quit on the Newport Blvd bridge over Coast Hwy going onto the peninsula about 35 years ago. Stopped dead, dead center of the bridge. Dead coil. Lucas, the Prince of Dead. Started later after a VERY expensive tow off the bridge. Joe H
Hoop you sure come up with some good tech explanations. So why would the OP's coil suddenly overheat after 20 miles? I have had a coil crack and leak oil out by leaving the key on. Would it be possible to have the dwell so high that the increased saturation time overheated the coil? How about bypassing the ballast resistor?
I think you nailed the 3 most likely causes of coil overheating. A damaged coil can short some windings, causing high current but low inductance, so low energy. As it gets hot the energy falloff weakens the spark until the engine quits making noises. Electronically switched circuits fail like this because the silicon stops switching around 100 C.
I bought a car once that the previous owner couldn't figure out. It would run down the road just fine for about 20 miles and then just die. Let it cool down 5 minutes and it would fire up and go another 20 miles. Turned out the wires were crossed on the coil.
make sure a ballast resistor is in place...should run at 7-9 Volts...you have to check it RUNNING......resistors don't work,unless current is flowing....ie Points working or breakerless ect.........
I has an Accel "super stock" coil that drove me nuts for quite awhile, acted like carb problems. Open the throttle and it had a hole...."lean out"....but it was the spark going out....
The only condenser problem I've ever had was in an off-topic car. The car would run for 15-20 minutes and just die with no warning. I'd wait 10 minutes or so and she'd start right up, only to die again in another 15 minutes. Changed the condenser and all was well. I had a coil in a '37 Chevy go bad. Once it was heated up and you'd stop for gas, it wouldn't re-start until it was left to cool with the hood up. Only happened in the real hot weather. The car would start by pushing and popping the clutch right after stopping. Got a new coil and everything was good.
When we first got my Son's rpu on the road it would run for about 10 miles and then shut down. We were thinking vapor lock and were chasing that issue, but he happened to touch the coil and it was really hot. While I ran to the shop in my car to get a new coil he put a wet rag on the coil and the car fired back up and he was able to drive to the shop. We originally had the coil mounted horizontally so we changed that to vertically, and we put a new coil on it. The car now has thousands of miles on it and has never shut down again, so yes, a coil can stop working when it gets hot. Don
I had a condenser go bad slowly in an old Ford van, on a trip. Started in Canada with a slight miss on the highway, then became worse to the point it would only go 60, then 50, then 40... Took me a long time to figure it out, thought I was having fuel starvation. Finally started playing with the points and noticed it made a difference but not a cure. Replaced only the condenser, in Washington, and all was well. The $2 fix was welcomed, but not the aggravation leading up to it.
I had a bought a brand new off road motorcycle that would quit after 5 miles. I took it back under warranty. Picked it up the new day, drove 5 miles and it quit again. I took it back and spoke to the head mechanic. He said it was bad gas. I told him the recommended Mobil so he pulled the gas cap, looked at it and said, the vent hole was plugged. I asked him if he had a motorcycle. He said yes, so I told him to bring it to work because if they didn't fix mine, I would take his on vacation. I told him the coils were bad and needed to be replaced. Guess what? They replaced the coils and it never had a problem again. I my case, it never misfired, it just quit. I've had condensors go bad but it never stopped running. I could limp the car home on half the cylinders.
Condenser failure usually has a fuzzy yellow instead of a sharp blue spark. Cars (Pre HEI /Current Limiting/Variable dwell) were built with carefully chosen combinations of primary resistance, coil current, and secondary loads. As we mix and match components we are much less likely to get it right. Throw in cheaply specced primarily off shore components and the margins for error shrink to non-existent. I have heard that GMC Bubba has a good source of high quality coils. Name brand quality components properly matched will minimize these bad experiences. As far as vertical coil mounting of oil filled coils, the factories mounted millions horizontally, but if it makes you feel better why not.
Had same problem. Thought I had an internal resistor on coil but did not. Run for twenty minutes and just die. Let it set for about 30 minutes or so and cranked right up. You need a ballast resistor or a coil that has a internal resistor.
Reminds me of when I was about 20 years old, I had bought a '58 Mercury that was about 200 miles away, and drove it away after buying it. After about 30 miles of driving, the engine would die. There was no spark when I checked it. I noticed there was a dent in the coil, and an oily residue below it, so I picked up a handful of snow, and used it to cool the coil down. The car fired right up, but again, would die after about a half hour of driving. Of course this was on a Sunday, and no parts stores were open, but I eventually made it home and changed the coil out the next Monday, solving the problem for good. ---John
I hear the "internal resistor" description quite a bit. All coils have one primary resistor. All the designing engineers do is vary the amount of windings of the primary for a different resistance factor if to be used on 12-volts or some other voltage. Ballast resistors on the outside actually do a better job of controlling the input current to the coil. A coil with a higher resistance factor in the primary winding simplifies the system but may also increase the internal temperature of the coil. The modern epoxy resin coils seem to take the heat better than the old oil filled ones but they aren't made for every application either.
The Jalopy Journal
