Hot Coil Causes

[plasticpig1972]

Went for a drive yesterday with the car club and when i stopped the Engine several times it did not want to restart.
The Coil Bosche Blue was very very hot and impossible to touch. After cooling for a few minutes the Engine started no problem.
So the question WHAT CAN CAUSE THE COIL TO OVERHEAT ?
I have fitted it away from the Engine in a cool place so not heat from Engine.
Do i need to fit a Resin filled Coil, could it be the Condensor is not doing it's job and causing the Coil to overheat.
Thanks in advance i'm all ears to listen to ideas.
Alan

[xtruss]

Some cars / coils need a ballest resistor to limit the current flow to the coil when the engine is running. It's found in the +12v feed to the coil.

[Penelope Stopit]

Thought all Bosch Blue were epoxy filled coils?

Measure primary winding resistance

Bosch Blue should be 3 to 3.5 Ohms. Bosch Blue is a 12 volt coil and no ballast resistor is needed

Have 4 thoughts on the problem

1) Coil is faulty

2) The coil isn't getting too hot, it's often hard to tell what too hot is without being able to compare with a substitute and also measure with a temperature probe

3) Coil is getting too hot due to an over-charging problem, coil supply voltage would be too high

4) Something else is failing when hot

Suggest that you go for a good run and quickly replace the coil with a cold one when the problem shows and see if she starts straight away, at least you will then know that it's definitely a coil problem or not

Also check charging voltage when hot with fault showing

[plasticpig1972]

Hi Penelope,
good idea, i just fitted a second Coil next to the existing one.
So when start problem arrives i will get out the car quickly and cahnge Cables to second Coil. Then see what happens.
Alan

[Penelope Stopit]

plasticpig1972 said:

i just fitted a second Coil next to the existing one

Great idea, good to have even when the problem's solved

[O mage]

Because this is an essential part of the tank system and you have up rated your coil you may need to re tune the ignition timing off spec to achieve the best results of it and for Your engine. This is best done by not going by the book which doesn't relate with an unknown quantity.(the only way to test the coil's inductance is with an lcr meter to measure the core under ac voltage. The best way tune this circuit is on the road, not with a strobe, drive the car at 30 put it in fifth and load it then advance till you just hear it pink then back it off just a tad until you cannot hear it start to pink, don't worry if your book timing mark is now off if Your engine is going pink it will do under load first. you should be looking for advancement with the higher spec Kv. (it will be off if you check it with a worn damper pully for instance). This way will tune your new coil to your existing capacitor/amp and improve the Q factor and if its resonating in epoxy instead of oil then it will overheat. Also make sure the coil body is earthed properly in it's new location as this temper's the field through the oil.