Hello brains trust. I see lots of articles where it is mentioned that a coil performs worse as it gets hotter but are there situations where a coil performs worse when its cold and gradually improves as it gets warmer? TIA

 

I don't think so, laws of physics, resistance goes up in the windings as things heat up.
Never had a coil stop working even in the coldest winter. It's not a piece of electronic equipment with micro processors that may be susceptible to cold, it's just a simple transformer.
Even microprocessors don't like heat.
Other bad things happen too, when a coil gets too hot, it breaks down the varnish on the windings and causes complete failure by causing internal shorting.

The big Lucas coil which was around 4 to 5 ohms achieves this by adding more windings of heavy copper wire, "expensive".

New coils achieve this by using thinner gauge wire, less wire to raise the resistance because it's thinner, but because the wire is thinner, they get very hot.

I've used a 3 ohm coil and have a 1.5 ohm resistor in a series in the primary windings to keep the current flow down and that in turn creates less heat.
Still plenty of point dwell to fire the plugs even at highway speeds.

Also, if it doesn't bother you, mount the coil on the inside fender-well, not at the top of the head where all the rad heat collects.
One of the worst places that Jaguar could put it, I think the thinking was that it would be cooled from the cars fan, but the problem is the shroud defeats that purpose.

Avoid Chinese coils.

 

Jeff is spot on. The coil failure modes are due to deterioration of insulation on the wiring & the cooling oil in the coil slowly oxidises over time until it becomes so thick that it ceases to circulate & cool and things get really hot leading to deteriorating performance & ultimately failure.

 

well that's it, I am relocating the coil to the inner wing. I never liked it mounted to the cylinder head anyway.

 

At least, it stays dry!

Jose, If you move the coil, are you also re-routing the spark plug cables around the back of the engine?

 

no Peter I would not do that. It is simple to move the coil, but rerouting all the cables towards the back of engine would require very long cables to then come back forward to reach the distributor and coil. I have new cables and sleeves, will leave them as normal.

What I am trying to decide is if to use the original "LUCAS" spark plug connectors or if to use the new "CHAMPION" connectors. The LUCAS connectors make more sense to me.

 

Why would one want to re-route the cables to the back of the engine ?
It will stay quite dry moving the coil near the front inner wing.
There is a thread somewhere where this has been discussed, I think the Mark 10 or some late model car had moved it there.

 

A few people have rearranged the air cleaner and the plug cables just for the aesthetics.

 

Ian Callum's car with HT leads routed to the rear & coil to inner wheel arch.

 

Makes for a nice clean engine bay.

 

I was playing with the coil to find a spot on the inner wheel housing to move it to.

I looked at the Lucas coil and it is dated 5/64. I don't know if it is good or bad.

I do have another known good coil from my1984 XJ-6 dated 6/83. I know it is good because it was fine when I replaced it with a XJ-12 coil after I learned that a 12 cylinder coil made the 4.2 engine run better. ( it does ).

The Question:
can I use the XJ-6 coil in the 3.8 engine ? Thanks.

 

Measure the resistance across the + and - terminals, if it's 3 ohms or above, then you may.
This assumes that you're not using a 1.5 ohm ballast resistor on your 3.8 engine.

If it measures 1.5 ohms then you must use a 1.5 ohm ballast resistor.

 

Thanks Jeff, no ballast. will check it for ohms and report.

 

Jose ~ I'm running a debranded Flamethrower 3 ohm 40,000 volt coil without ballast resistor. Starts on the button & performs faultlessly.

Now has a correctly positioned & correct Lucas sticker/decal on it. (for SA CKD cars anyway)

 

Glyn, Very nice, detailing. I told the machine shop to paint the 3.8 block in bright yelliow so I can easily see leaks They had a feast laughing, but I pointed at the painted red and green and gold V8 blocks they have there. Black absorbs heat I told them.
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Quagmire:
the XJ-6 coil cable is a push-on connector at the coil and I am replacing all HT cables with screw-on connectors at the dist. cap.

so I need a push-on cable to cut the end and adapt the screw-on end.

 

Thanks ~ as you can see we were still working on her at that time. Yes HA12 coils were 30KV and only supposed to have push on connectors from 68. My car originally had acorn nuts everywhere but I went to push on for the coil. That said a friend has an unmolested 66 with push on coil & acorn nut distributor cap so who knows. My original Lucas Coil had done 90K miles so I tossed it.

 

Lucas coils

LA12 = 20Kv standard coil (6" long)
HA12 = 30Kv high energy coil (7" long)
SA12 = 40Kv sports coil (1/8" thicker than HA12)

Note: MA12 were motorcycle coils, BA12 were internally ballasted coils (not correct ~ see below)

 

Where is this BA12 internally ballasted coil, as far as I know, there is no such thing ? Please give me a link.
Manufacturers don't put the ballast resister inside the coils, it would get too hot, in order to increase the resistance they add more windings to the primary circuit, or use thinner copper wire.

 

Jeff. I pulled this info years ago from the UK E Type forum into a Word document. I will research whether they are talking BS. Alan Wiede & I were doing research on correct S Type decals & positioning for the Register.

 

Here's one for sale. I will do more research. I believe the decal says Use with Ballast Resistor.

https://en.todocoleccion.net/spare-c...-12~x130765556