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Old 06-04-2019   #1
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0verheating coil

Hi I have had a problem with the car ( 1972 500 L ) cutting out after about 6 or 7 miles . I have gone through all the other things like tappets, fuel pump, filter in tank etc. Then I felt the coil which was red hot. It has a 650cc engine and I have one of the exhausts that bring both downpipes to the front to get away from the starter. I tried leaving the engine cover open and hey presto it was fine .I have now moved the coil behind the grill above the engine cover with some protection from the elements quite an easy fix. Has anybody else had this problem. It is a new coil of the correct voltage and it is wired the correct way round with contactless ignition .
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Old 06-04-2019   #2
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Re: 0verheating coil

Sometimes I think it's down to the quality of some of the new ignition components. I've had cars that are still using 50 year old ignition coils and condensers that are trouble free. I've had other cars where I've replaced the coil and condenser with newly manufactured ones and have had problems. At one time you could buy new components and never have to worry about quality issues! There have been lots of complaints about newly manufactured Lucas components. I had problems with a new Lucas coil on another car and ended up replacing it with a blue Bosch coil that works perfectly. My 500F is running with a battered coil that's probably as old as the car. I've not had any issues with it overheating, but it's mounted on the left side of the engine compartment so is unaffected by exhaust heat.
If the coil overheats again, and you've got a meter, you could check the resistances of the primary and secondary coils (while it's still hot) to see if it's still within spec.
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Old 06-04-2019   #3
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Re: 0verheating coil

Iíve replaced mine with a Viper dry resin ( not oil filled ) coil. Along with all new components for the ignition. Coil is placed in original location. So far, so good. Still bloody too hot to touch thou. So my advice, donít touch it

Rob
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Old 06-04-2019   #4
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Re: 0verheating coil

I have replaced mine with as you say a viper and it got about twice as far before breaking down .After leaving the engine cover open I did about 30 miles some of it on the motorway with no problem.
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Old 06-04-2019   #5
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Re: 0verheating coil

totally agree with HOBO1960, we had the same problem with another classic car, fitted a new coil and after 6 or7 miles the coil was red hot and if the engine was switched off the car wouldn't start again till it had cooled down. We fitted an old coil, (very old) and had no more problems, I have had similar problems when fitting a new condenser to my fiat 500, re fitted the very old condenser and had no more problems for 4 years. If I am at an autojumble and see any new old stock coils or condensers I will buy them
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Old 07-04-2019   #6
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Re: 0verheating coil

Quote Originally Posted by phoenix1 View Post
Hi I have had a problem with the car ( 1972 500 L ) cutting out after about 6 or 7 miles . I have gone through all the other things like tappets, fuel pump, filter in tank etc. Then I felt the coil which was red hot. It has a 650cc engine and I have one of the exhausts that bring both downpipes to the front to get away from the starter. I tried leaving the engine cover open and hey presto it was fine .I have now moved the coil behind the grill above the engine cover with some protection from the elements quite an easy fix. Has anybody else had this problem. It is a new coil of the correct voltage and it is wired the correct way round with contactless ignition .
Mine is also getting red hot, or hotter than the sun as someone else mention here before!! can you please post a pic about your coil new location? It is one of the ''must solve'' problems in my list.
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Last edited by gordinir8; 07-04-2019 at 18:53.
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Old 08-04-2019   #7
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Re: 0verheating coil

I will upload some pics as soon as I get to the bottom of this problem. While I was out driving today my coil packet up. This was a new Viper dry coil which I thought would be better at withstanding the heat but no.There is no over voltage ( I have a small voltmeter fitted ) I have checked voltage at the coil but all ok . Its a mystery .
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Old 09-04-2019   #8
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Re: 0verheating coil

Today ( Tuesday ) I thought I would try to get to the bottom of this problem. When I bought this car (500 L ) it was completely disassembled I bought new plugs leads cap and converted to contactless ignition as well as a new rotor arm . I thought about the overheating and came to the conclusion the coil must be working a lot harder to get this hot. I decided to meter all the ignition from the tip of the plug to the end of the lead that pushes into the cap. I found that one of the only parts I didn't renew the plug extenders had a much higher resistance than the other. Therefore this would load the coil more . I have ordered two new ones and I will let you know the outcome.
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Last edited by phoenix1; 09-04-2019 at 15:36.
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Old 13-04-2019   #9
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Re: 0verheating coil

Hi I also have an overheating coil. on mine I have a 123 electronic ignition and I'm worried I might burn it out. I'm looking at the voltage regulator but have found its the newer electronic version off a 126 so I think it's unlikely to be that. What next I'm not sure but breaking down after 10 mins driving is not a pleasant experience. Anybody with ideas ?
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Old 13-04-2019   #10
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Re: 0verheating coil

I also read somewhere that an owner had placed two coils next to each other to see how hot it gets from the engine heat. The answer was that only the coil being used got hot which surely means in can't be caused by engine heat but from to much current passing through the coil .
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Old 14-04-2019   #11
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Re: 0verheating coil

So, this is bugging me somewhat. Iíve not had a failure or breakdown due to the hot coil. But I would like to get to the bottom of it.

If you have a coil at 3ohms then 12 volts means the draw will be 4amps. 48 watts.

I measured my coil primary resistance and observed reading of 2.7 ohms.
Ay 12v, this equates to 4.4 amp and 53 watt draw. Or an approx 10% increase.

The coil is designed to dissipate heat within its design parameters. But in my case the current draw is higher so will generate additional heat which maybe cannot be dissipated and builds up over engine run time. Iíve used 12v as an example but of course the generator and voltage reg will provide more depending upon RPM.

Iíll get a meter on the plus feed to the coil when the engine is on full choke to see what the V supply is. I suspect it will be around 13.

Rob
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Old 14-04-2019   #12
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Re: 0verheating coil

OK so some more info. The meter reading on full choke and maximum seen with high revs post a 20 min drive on the coil plus is 14.4v

Mmm, this seems too high. I have an electronic voltage reg fitted. But when I refer to my rare ( maybe?) English version of the Fiat workshop manual. It does mention regulator output at 14.2 +- 0.3 volts. So possible up to 14.5 is within design limits. See picture as below.

The other interesting point is that the manual states that the coil should be 3.2 ohm minimum Also as per picture enclosed.

So new calcs based updates on the voltage output of 14.4:

3.2ohm fiat spec = 4.5 amps / 64.8 watts
2.7ohm, my coil = 5.33 amps / 76.8 watts

I think the only option is to find a coil that is rated at 3.2 ohm or whack on a 0.5 ohm ballast resistor.

I would be indebted if any of you could measure the plus coil side at high RPM to confirm readings?

Opinions ??

Rob
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Old 14-04-2019   #13
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Re: 0verheating coil

More research. Bosch blue coil 0221119027 is circa 3.4 ish ohms. I will order and fit one soon. Boschís on line selection tool gives this coil for the 500. This coil is vacuum filled. I looked at Beru coils which also are around 3.3 ohm but these are oil coolled. Lot of people fitting the blue coil for older classic cars and report good findings. Maybe the more modern cars have better voltage control and regulation?

I also suspect that people who have a very old coil, will find the resistance higher on the primary. Maybe even higher post years of use? I should have never replaced the coil in the first place

Anyway, Iím going this route. Will report back the findings.

Rob
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Old 14-04-2019   #14
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Re: 0verheating coil

This thread explains a lot of what youíre looking for. https://www.fiatforum.com/500-classi...0=#post4183980

Both myself and Peter have been running Bosch Blues for a while. Well I donít anymore as I donít have a distributor on my 650 engine and it now has a dry twin coil. But when I had the 500 lump in the car the coil was fine. Itís what 123 recommend to use with their electronic ignition.
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Old 14-04-2019   #15
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Re: 0verheating coil

Ha! if only we had tried the search function first

Still, good learning curve for myself and others. Looks like my conclusions are drawing a parallel with the other thread. Iíve got new Bosch blue arriving tomorrow. Look forward to getting the meter on it.

Cherrs
Rob
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