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Ignition coils go bad every other winter?

4K views 5 replies 3 participants last post by  voxmagna 
#1 ·
I have had my 2007 Eos 2.0T for 7 years now, and it seems every other winter as soon as we have a few 20 deg or colder nights I have one or more ignition coils fail. Nothing worse on a cold morning then for your car to all of a sudden run terrible or not start at all. At least I am a pro at changing them now. I have tried replacing them with OEM VW parts from the stealership, Bosch, Denso, and now just the cheapest ones on Rock Auto because it seems like a sure bet that I will get a failure as soon as it gets cold in 2 years. Does anyone else have this problem? Am I doing something wrong?
 
#2 · (Edited)
I have a 2007 Eos owned since new with a 121,000 miles. Never had that issue. There was a recall for the coils early on and I had mine done, even though it didn't seem to be needed. Either you have been victim to a string of bad coils or have some type of installation issue or an electrical issue or some type of spark plug over heating issue or problematic spark plugs. Are they properly gapped? See if someplace like Advance Auto can loan you the use of an Infra Red thermometer. Check and see if any of the cylinders are running hot. Maybe the heat is killing the coils. May seem like a wild idea but seems worth investigating.
 
#3 ·
Agree, What seems to kill these coils is extreme changes in heat. The high voltage winding uses very fine insulated wire and the whole assembly is dipped in some kind of plastic to keep it all sealed. With extreme changes of heat the copper windings and plastic can expand and contract at different rates causing the HT winding to break. In really bad cases I have seen fine cracks visible in the molded plastic (check yours).

The damage was probably done during a hot Summer when the insulation breaks, but you only see the first faults when dampness penetrates in Winter? MY07 diesel doesn't have this but later VAG vehicles have an engine bay temperature sensor. When they park after being run hot, the engine fans can come on for 5 minutes or so to reduce the engine bay temperature. Although this is important for diesels with a hot dpf, it also give protection to sensitive parts (or coils) reducing thermal shock. It may be something V.W can do with an ECU software update so worth checking if there is one for your VIN. I don't know if they have actually added a thermal sensor, but my suspicion (for diesels) is they might use the temperature output already there from the exhaust sensors to put fans on when the ignition goes off.
 
#5 ·
Yes, the fan does run when I shut the engine off in the summer heat, but only for a few seconds at most. It has operated like that since purchased (with 50k miles). I replaced the plugs the first time I changed the coil packs with VW OEM plugs. Have not changed them since. I will definitely have to check the heat on warmer days. Do any of you have a feel for what the temperature at the coil packs should be?
 
#6 ·
A good start. I would attach a 'K' type bead probe and digital thermometer to a coil. Heat is generated inside the coil when it's working, so you could first do some surface temperature measurements idling with the hood open. Then comes the local 'ambient' which is the temperature in the engine bay and any hot parts underneath like the cyl. head or worst the exhaust manifold which will push up the coil temperatures considerably. Your first port of call is to try and find out why others with a similar car don't seem to have the same problem, although coil failures seem very frequent across the VAG models.

If you draw a blank for the easy things or the coil temperatures run too high with the hood open, you then start improving the design if that's possible and become the only one never having the coil thermal issue which causes it to fail again. Waiting for a redesigned/improved coil from VW would be like forever. IMHO a coil surface temperature exceeding 70C would worry me? It might sit around 60C operating with good free air circulation (hood open) but depending on how air circulates in the engine bay and when stopped, that surface temperature might rise to 100C +. The way HT coils (aka transformer) is designed is it will have a 'core' as most cores heat up inside fully enclosed encapsulation, the coil becomes less efficient at higher revs and will take more power causing more heating. You may remember that HT coils used to be larger and oil filled, or in a mower their core is exposed and can cool.

Redesigning the Bad Boy coils: I don't have your engine but if measurements show heat is coming up from hot parts underneath, consider a sheet of ali fitted underneath to act as a heat deflector. If there's sufficient space around and between each coil, consider a wrap around sheet of 22AWG aluminium with a wide 'tab' formed like a large 'P' clip. use some heatsink compound under the wrap around and paint it black. Confirm its effectiveness with surface temperature measurements. If you pass the redesign test you can pass Go and apply to V.W for a Job! Finally, the coils probably have quite a power overhead producing the heat and may work just as well with a small series resistor. Reducing their power by even 10% would have a big effect on the amount of internal heat they generate. Let us know if you get the V.W job!
 
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