30.000 km OEM-B-coils with heatprotection..
04-30-2014, 03:06 PM
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30.000 km OEM-B-coils with heatprotection..
Inspected my 30k km B-coils (changed the OEM ones for OEM-B-type at 10k km; odometer total 40k km.) equipped with protection against heat from the engine; protection made from 2x2mm layer ceramic tape 8 inch wide.
Bottom looked as new!
Decided to apply an extra double layer, total thickness 8mm; compressed 6 mm.
Bottom looked as new!
Decided to apply an extra double layer, total thickness 8mm; compressed 6 mm.
04-30-2014, 03:09 PM
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How are the igniters doing inside the coils? Did you test those too?
White spots don't mean failure, and coils can fail without white spots.
I agree that protecting them from heat is probably going to result in longer lasting coils, however you aren't really showing any evidence of how well your shielding worked.
White spots don't mean failure, and coils can fail without white spots.
I agree that protecting them from heat is probably going to result in longer lasting coils, however you aren't really showing any evidence of how well your shielding worked.
04-30-2014, 03:33 PM
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No, I did not inspect the coils further; only measured the resistance between the different pins of each coil as a matter of interest; cannot remember exact value's, however data from all 4 coils were more or less the same.
Indeed, lacking of white spots are not a sign of 100% coils.
No, I can not show any evidence in relation to the heatinsulation, however I have seen pictures in the past of coilbottoms from (non-heatinsulated) coils that failed, which all showed white spots at low mileage {plus maybe other (inner)/causes of failure}.
Anyway I will replace my coils every 20-30.000 mls incl. cabels and sparkplugs; have 3 cpl OEM-spare sets in my garage.
I was only interested to see how the coilbottoms were with the heatinsulation and wanted to share this.
In Germany some specialist supply the heatinsulation now free with coilorders; generally a number of Rex-drivers tend to pay more attention to the heatexposure of the coils.
My 231 hp runs still wonderfull.
Indeed, lacking of white spots are not a sign of 100% coils.
No, I can not show any evidence in relation to the heatinsulation, however I have seen pictures in the past of coilbottoms from (non-heatinsulated) coils that failed, which all showed white spots at low mileage {plus maybe other (inner)/causes of failure}.
Anyway I will replace my coils every 20-30.000 mls incl. cabels and sparkplugs; have 3 cpl OEM-spare sets in my garage.
I was only interested to see how the coilbottoms were with the heatinsulation and wanted to share this.
In Germany some specialist supply the heatinsulation now free with coilorders; generally a number of Rex-drivers tend to pay more attention to the heatexposure of the coils.
My 231 hp runs still wonderfull.
04-30-2014, 03:37 PM
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The pin resistance specs in Mazda's test will pass a coil that is misfiring a lot, so hard to put any weight on that either.
But yes, it looks like the heat shielding is doing it's job as far as reducing the heat saturation. Maybe someone else will eventually determine the actual impact on the coil ignitors.
But yes, it looks like the heat shielding is doing it's job as far as reducing the heat saturation. Maybe someone else will eventually determine the actual impact on the coil ignitors.
04-30-2014, 05:42 PM
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04-30-2014, 06:49 PM
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1) Well, imho this solution will not work sufficiently since the mounting plate is heavily heated by heat radiation from the hot engine.
Furthermore the mounting plate being fixed on the engine itself is receiving additional heat via the mounting bolts.
Summarized, in that situation the heated mounting plate still can radiate additional heat to the bottom of the coil; eventually at higher temperatures than the average inner temperature of the coil (100-150 degr. F.) which is already struggling to get rid of its own (inner developed) heat. The only advantage is an air gap with some circulation of fresh air, which however is not enough since this radiation is overriding the cooling effect of the air stream in the gap.
2) The twin (or double twin) layer of ceramic tape (heat resistant up to 2900 degr. F.) insulates the bottom of the coil effectively from the mounting plate which enables the coil to cool itself via the rest of the upper/sided surfaces (excl. bottom). In this set-up the bottom of the coil is relatively "cool" due to the low temperature of the upper side of the ceramic tape. The final result is a considerable lower temperature of the coil compared with the situation as per 1).
Furthermore the mounting plate being fixed on the engine itself is receiving additional heat via the mounting bolts.
Summarized, in that situation the heated mounting plate still can radiate additional heat to the bottom of the coil; eventually at higher temperatures than the average inner temperature of the coil (100-150 degr. F.) which is already struggling to get rid of its own (inner developed) heat. The only advantage is an air gap with some circulation of fresh air, which however is not enough since this radiation is overriding the cooling effect of the air stream in the gap.
2) The twin (or double twin) layer of ceramic tape (heat resistant up to 2900 degr. F.) insulates the bottom of the coil effectively from the mounting plate which enables the coil to cool itself via the rest of the upper/sided surfaces (excl. bottom). In this set-up the bottom of the coil is relatively "cool" due to the low temperature of the upper side of the ceramic tape. The final result is a considerable lower temperature of the coil compared with the situation as per 1).
Last edited by Rudolph; 04-30-2014 at 06:59 PM.
05-01-2014, 07:01 AM
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Information from the UK-forum:
The issue here is that the output of the coil produces voltages well into the kV range, that have to be electrically insulated from anything that is close to ground potential (i.e. the mounting plate). This is why they are encapsulated in the black potting resin. If the manufacturing processes are correct and tightly controlled, this resin should be vacuum sealed and free of any voids (air pockets provide an easier breakdown path for the high-voltage produced).
It will also get hot from it's own operation, and without effective heat dissipation, the impedance of the coil will increase over time, as well as degrading the dielectric properties of the potting resin. There will become a point where the coil impedance is high enough that the high-potential breaks down to the grounded mounting plate, rather than across the spark plug (causing the cut in ignition that can happen with high-mileage coils, the severe pitting on the bottom is high-voltage erosion).
This solution provides heat dissipation and provides greater voltage stand-off. I'd be interested to see what they are like after 25k-30k miles.
RX8 Owners Club • View topic - 30.000 km OEM-B-coils with heatprotection....
The issue here is that the output of the coil produces voltages well into the kV range, that have to be electrically insulated from anything that is close to ground potential (i.e. the mounting plate). This is why they are encapsulated in the black potting resin. If the manufacturing processes are correct and tightly controlled, this resin should be vacuum sealed and free of any voids (air pockets provide an easier breakdown path for the high-voltage produced).
It will also get hot from it's own operation, and without effective heat dissipation, the impedance of the coil will increase over time, as well as degrading the dielectric properties of the potting resin. There will become a point where the coil impedance is high enough that the high-potential breaks down to the grounded mounting plate, rather than across the spark plug (causing the cut in ignition that can happen with high-mileage coils, the severe pitting on the bottom is high-voltage erosion).
This solution provides heat dissipation and provides greater voltage stand-off. I'd be interested to see what they are like after 25k-30k miles.
RX8 Owners Club • View topic - 30.000 km OEM-B-coils with heatprotection....
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