Cooling coils

[manuRx8]

Has anyone measured the temperature that the coils reach in normal use?

I bought the Versatuner and started to change parameters and adjust some maps. When it was the turn of the coil permanence map (DWell), before touching anything, I decided to look at the temperature reached by the coils and thus control possible overloads when the loading time began to increase.

I have taken an unpleasant surprise: in normal conditions the coils were always above 80 ° C, exceeding even at times the 100 ° C soon after you squeeze the engine or catch a jam.

I have also observed that these temperatures go hand in hand with the temperature of the oil, which has a certain logic to be located very low, which receives the heat that rises from the Carter, which adds to the internally generated by the coils.

That is why I decided that before modifying the permanence I had to do something that would allow the coils to "cool" something.

First, I modified the support so that the coils are separated and so that some air can circulate below them.


I have also put a fiberboard under the support, to reduce somewhat the heat it receives by radiation from below.



Finally, I have put a flexible tube from the front to bring fresh air to the coils.




With these modifications I have achieved that the temperature in the coils drops between 20 and 30ºC with respect to that of the oil.

It only approaches that of oil when I'm in traffic jams or very slow traffic, but as soon as you get some speed the temperature drops.

Circulating above 90 km / h the temperature is always maintained between 50 and 60ºC

[warpc0il]

You're not the first to go down this route, which was popular 10 years or so ago, before the Mazda C-spec coils were released.

Unfortunately there's no evidence that local cooling helps longevity or performance.
There was some circumstantial evidence that directed air cooling can reduce coil life, which was put down to the "thermal shock" or at least the changes in core temperatures. The coils are designed to run at high temperatures and not to be heated and cooled while running.

The earlier coils suffered from a breakdown of the internal insulation but the trigger was most likely either a high resistance (bad connection) or low resistance (tracking) of the poor quality HT leads, especially the plug end caps. This would result in excess energy within the coils causing insulation breakdown. The visible heat damage was a secondary effect, not the primary cause.

The C-spec coils are significantly more robust and, in combination with quality aftermarket HT leads, are as (or more) reliable than any other system, without any changes to the mounts etc.

[350matt]

Modern coils can cope with very hot temps
our limit at work is 120 degC and more for some of the more specialised stuff

[manuRx8]

The sudden changes in temperature I had already considered and therefore the jet of air is not directed towards the coils, but towards the space that I created between the support and the coils themselves, seeking to reduce the heat that reaches them from the oil sump and that contributes to increase its temperature.
So you think it is not necessary or even counterproductive to refrigerate them?

[warpc0il]

The coils will have a design optimal working temperature, which will be defined at some point within the core and higher than measured at various parts of the outer casing.

Mazda, well aware of the excess engine bay temperatures and resultant issues created in the later RX7s, with their twin-turbos and everything squeezed-in so tight, initially designed the RX8 engine bay to be cooled by an opening below the front number plate, within the "mouth grill".

However, during pre-production testing, even in high-ambient, they discovered that the excess cool air chilling the intake side of the engine was causing thermal stress to the engine block and, at lower ambient, creating condensation within the oil system.

If you look through the diamond-shaped holes below the front numberplate you'll see they're blocked-off, and if you remove the bumper you'll find the rubber blanking panel they had to add for production, to stop cool air directly entering the engine bay.

One of the design team was quoted as saying "This panel could be removed if you were running full power for long periods, with less foreword motion" - which is engineer's speak for "Drifting"

[Rudolph]

I once measured the coil temp. and that from the coil base plate with engine in full operation........
The coils in operation are up to max. about 50-70 gr. C. .......
The coil base plate, due to heat radiation from the engine block is up to 90 Gr. C.
(engine block = 90-100 Gr. C outside case wall temp. / measured)
So any insulation does result in elimination of additional heating up by the hotter coil base plate to the coils ..........

[Rudolph]

*****

[warpc0il]

That insulation won't cause any harm and may (or may not) do some good.

[manuRx8]

The coils will have a design optimal working temperature, which will be defined at some point within the core and higher than measured at various parts of the outer casing.

Mazda, well aware of the excess engine bay temperatures and resultant issues created in the later RX7s, with their twin-turbos and everything squeezed-in so tight, initially designed the RX8 engine bay to be cooled by an opening below the front number plate, within the "mouth grill".

However, during pre-production testing, even in high-ambient, they discovered that the excess cool air chilling the intake side of the engine was causing thermal stress to the engine block and, at lower ambient, creating condensation within the oil system.

If you look through the diamond-shaped holes below the front numberplate you'll see they're blocked-off, and if you remove the bumper you'll find the rubber blanking panel they had to add for production, to stop cool air directly entering the engine bay.

One of the design team was quoted as saying "This panel could be removed if you were running full power for long periods, with less foreword motion" - which is engineer's speak for "Drifting"

I have read in multiple forums that same statement about the reasons why the upper grid is covered, but I really have to ask, has anyone seen it reflected in any technical note of Mazda? or simply "we have heard someone who says he has heard someone who said ...".

In addition, I have always been surprised that some of the defenders of that theory and advise not to remove that cover then, in their cars, change the front defense by other aftermarket with huge front openings.

In my opinion, that is not the cause, because:

At the rear of the radiator, its upper half is covered by the battery and admission boxes; therefore, all the air that passes through the radiator, both the one that can enter through that cover and the one that passes through the lower opening, has no choice but to exit through the lower part of the transverse bar in which support the battery and filter box, that is: both if we open the grid and if we do not open it, the air will come together in the lower part and will affect the same areas of the engine block and in no case in the intake area that is almost all higher than the crossbar . In any case, I insist, the air that can enter through that grid, must always pass through the radiator and therefore never send "fresh air directly to the engine block"

My theory about that cover is another:

As the radiator is so inclined, if we open the upper grille, the air that hits the top and does not get through the radiator will move downwards, pushing and deflecting the air that reaches the lower areas, so the flow of Lower air will be greatly impaired (especially at high speeds).

With the grid covered, the air entering through the lower mouth, will form inside the nose an "air bag" that will go through the radiator, even in the upper area and without altering the inflow in the lower area.

Hence the importance of keeping the foam seals around the radiator in good condition so as not to leak in "that air bag".

In my case, almost 3 years ago I decided to bet on the maximum air flow:

• I removed that front cover

• I have modified the battery holders and air filter box to remove the blockage of the air in the upper part of the radiator (orienting the flow downwards anyway)

• I have placed some baffles in front of the radiator, to direct the air flow of the 2 frontal entrances and to have them incline perpendicularly to the radiate.

I already have more than 20000km with these modifications: I think it has greatly improved the cooling in summers and in the winters I have never seen condensation in the oil.

[manuRx8]

I once measured the coil temp. and that from the coil base plate with engine in full operation........
The coils in operation are up to max. about 50-70 gr. C. .......
The coil base plate, due to heat radiation from the engine block is up to 90 Gr. C.
(engine block = 90-100 Gr. C outside wall temp. / measured)
So insulation does result in elimination of additional heating / loading of the coils ..........

Rudolph,
I am happy to see that we agree on our conclusions and we have even agreed on how we approached the problem and its possible solution.
From the beginning I had attached a temperature sensor on the back of the 2nd coil, with which I can see the temperature of that central coil, continuously, on a gauge in the cockpit.

I also started by inserting a ceramic blanket between the bobbins and the support, but sorry it noticed improvement, so I went to separate something coils (1 cm approx.); but as I still did not get a significant improvement, I decided to go for it and try the solution I described at the beginning of the topic.

As in the end I have greatly increased the separation from the support, I replaced the ceramic blanket with a fiberglass plate (recovered from an old electronic project). In addition, to facilitate the cooling of the rear coils by the air flow, I chose to mount them step by step.

The insulation alone, without the air flow, hardly has any effect since the heat that accumulates inside the engine compartment is very high. This is well appreciated when you are standing in a traffic jam, as the coils quickly rise to the same oil temperature. However, once you start the march and start to get air through the tube, the temperature drops little by little to stay between 20 and 30ºC below the oil.

I agree with you that at least it is convenient to isolate and separate the coils from the support, to avoid adding to the internal heat the irradiated by the motor.

[warpc0il]

I have read in multiple forums that same statement about the reasons why the upper grid is covered, but I really have to ask, has anyone seen it reflected in any technical note of Mazda? or simply "we have heard someone who says he has heard someone who said ...".

I was an Systems Solution Architect for Ford of Europe and providing internal consultancy for many activities with the Ford group worldwide, including Mazda and the team performing the pre-production testing of the RX8.

The results of the testing and the subsequent decision to fit the blanking panel was shared with me, first-hand.

[manuRx8]

I have read in multiple forums that same statement about the reasons why the upper grid is covered, but I really have to ask, has anyone seen it reflected in any technical note of Mazda? or simply "we have heard someone who says he has heard someone who said ...".

I was an Systems Solution Architect for Ford of Europe and providing internal consultancy for many activities with the Ford group worldwide, including Mazda and the team performing the pre-production testing of the RX8.

The results of the testing and the subsequent decision to fit the blanking panel was shared with me, first-hand.

Thanks for your answers warpcOil,

Finally someone who has obtained first-hand information about that covered grid. If as you say you have discussed the issue with Mazda engineers in the pre-production stage of the Rx8, you can certainly clarify the doubts that have led me to think about the falsity of those claims.

As I mentioned before, I think that all the air that goes through the radiator, both the one coming from the lower opening and the one coming from the upper rack uncovered, should come out "mixed and hot" by the bottom of the crossbar (I think it has no other possibility since the upper part is covered by battery boxes and air filter). According to this, the only effect that the upper opening could make would be to increase the volume of circulating air (approximately 20% or 30%). Am I wrong or is there some other effect that I have not appreciated?

According to the appointment of the design team, which you mentioned in the last show, only the panel should be opened to improve the cooling when used to Drifting.

One of the design team was quoted as saying "This panel could be removed if you were running full power for long periods, with less foreword motion" - which is engineer's speak for "Drifting"

This leads me to think about the problems of refrigeration that has the Rx8 in normal use and we discussed a thousand times in this and other forums. If we pay attention to the comment of the member of the design team, the Rx8 has no heating problems, in fact it has an excess of cooling and therefore it has had to close part of the front air intake.

I do not know where those tests were made, but in warm areas, with temperatures close to or even higher than 40ºC, I can assure you that the air that comes out of the back of the radiator is not exactly "cold air".

I repeat, I am sure I am wrong and there is some other effect that I have not appreciated and that you, with your experience in Systems Solutions, could explain to us ...

[warpc0il]

I think you're getting confused about a couple of fundamental items.

With everything correctly in place, only air entering through the lower opening is ducted to and through the radiator.
The radiator surround should be sealed to ensure that none of this air can escape outside the core - these seals are often missing, which significantly reduces the efficiency.
The air-conditioning heat exchanger is sandwiched in front of the radiator, so it gets the initial cooling chill.
The air exiting the radiator should be hot, sometimes very hot, as that's what the radiator is meant to do, when the thermostat is open.
Separation of the engine bay air and incoming cooling air is critical and any air entering the engine bay has no route to the radiator, unless a panel has been removed and not replaced.
The two variable-speed cooling fans are controlled by the PCM, which runs a complex algorithm to manage the cooling effect, noise and alternator load. These fans even have a different number of blades to ensure that there's no acoustic beat when they're both running at the same speed.

The tests were made in real world locations down to -20C and over +40C, plus many hours in climate chambers where temperature, humidity and wind chill can be controlled to replicate extremes beyond those found in even the wildest locations.

[manuRx8]

I think you're getting confused about a couple of fundamental items.

With everything correctly in place, only air entering through the lower opening is ducted to and through the radiator.
The radiator surround should be sealed to ensure that none of this air can escape outside the core - these seals are often missing, which significantly reduces the efficiency.
The air-conditioning heat exchanger is sandwiched in front of the radiator, so it gets the initial cooling chill.
The air exiting the radiator should be hot, sometimes very hot, as that's what the radiator is meant to do, when the thermostat is open.
Separation of the engine bay air and incoming cooling air is critical and any air entering the engine bay has no route to the radiator, unless a panel has been removed and not replaced.
The two variable-speed cooling fans are controlled by the PCM, which runs a complex algorithm to manage the cooling effect, noise and alternator load. These fans even have a different number of blades to ensure that there's no acoustic beat when they're both running at the same speed.

The tests were made in real world locations down to -20C and over +40C, plus many hours in climate chambers where temperature, humidity and wind chill can be controlled to replicate extremes beyond those found in even the wildest locations.

Thank you very much for all that information about the elements associated with refrigeration, I already knew it, but surely there are many colleagues who did not know it and it always comes in handy.

I do not understand very well what you mean by this: "the air that enters the engine compartment has no route to the radiator, unless a panel has been removed and has not been replaced."

And you forgot to say that in the complex algorithm is also included the Air Conditioning, starting the fans in slow mode when the compressor is activated; but in general almost everything you indicate is correct.

In any case, the key question remains in the air:

If we remove the lid of the grid, how and where does the "cold air" coming through the grid reach the block to cause those effects of thermal shock and condensation in the oil that you mention? since the only route that I see is the same route that uses the air that enters through the lower mouth and in my opinion they would arrive mixed to the motor bay

[Phil Bate]

I was fiddling away removing my coil bracket earlier, wondering why it was taking so long to undo the bolts when I suddenly remembered that many moons ago I had drilled out the bolt holes and fitted grommets to isolate it from the engine and A/C compressor -

IMG_20190511_235827 (Large).jpg

This was more related to electrical conductance experiment reasons than heat transfer at the time, but I thought of this thread as soon as I saw it and thought it might be of interest.