Last year at the track we had a great time. It was the first year with the fans located behind the radiator as "pullers" which seemed to completely cool the car down on the street even with the AC on. The hood vents helped even further and even seemed to pull the car down o the track a bit more at speed. We added a set of side air dams and door bars, both of which changed the cars feel and appearance dramatically. We even upgraded to Evan's waterless coolant.
We really hoped this would be the year that the car would be "unlimited" and that we would both find our driving to be the limiting factor, not the car. Keeping the thing cool had been a continual battle the two years before that it had been tracked but now it seemed to be fine on the street so the track should have been a piece of cake, right?
The car was great for about 10 laps until we started to see the temps rise. I had installed an electronic AutoMeter gauge (much more accurate than the Miata dash gauge) and noticed it climbing up past 220 degrees. I kept at the throttle and it kept climbing up past 250, the limit of the gauge. I found that if I throttled it back a bit, threw the car in 5th and took a "rest lap" the temps would come back down and I could jump back in the fray. Needless to say, this is not ideal.
I took the winter to try and figure out what went wrong. I figured the shroud I had made for the radiator was too restrictive at speed. The ironic part is that with the fans in front of the radiator as "pushers" (the original configuration) the stock gauge would never show an issue on the track. On the street the car would overheat the moment you put the AC on. With the shroud the situation was reversed, fine on the street, hot on the track.
So I set about redesigning the shroud. I purchased two new TriPac fans from Monster Miata (the original ones were almost seized-maybe contributed a little to my overheating issue...) and a set of "Pressure Relief Flaps" from Spal that should let the air pass through the shroud at speed but still seal it up when the fans are on. I also integrated two new high-amperage relays into the shroud itself and built a small harness and plug for it so that everything would be easy to remove.
Earlier this year I removed the original unmodified or chipped A9L ECU and swapped in a MegaSquirt II PNP unit from DIYAutotune. Originally I had my fans running of a Miata thermoswitch that was placed in the Ford thermostat housing neck.. One of the reasons I went with the MSII was it's ability to run fans via the ECU's coolant temp sensor. To hook it up I made this small adapter harness on the left. The harness goes between the MSII and the Ford harness adapter and breaks the four unused idle wires out so I can use them.
It's just amazing the freedom a programmable ECU gives you over a stock unit. Using TunersStudio I configured the MSII to turn the fans on at 200 and off at 195. Set up like this I get a consistent 198-210 degree running temp even with the AC on. We'll see if it keeps those temps at the track.
Oh, and on a side note regarding the 250+ temps on the track last year via my Autometer gauge and the "normal" readings on the stock gauge the year before: Currently Tuners Studio is showing that my Autometer gauge is running consistently 15 to 20 degrees higher than what it is showing. I'm not sure if this is a problem with the gauge or the ground to it but chances are my temps last year were more like 230, not 250. As far as the stock gauge is concerned, I read at a few different sources on the web that the stock gauge is set to show "normal" at anything between 150 and 210 degrees. The first half of the gauge is the 0 to 150 section, the needle hardly moves at the center between 150 and 210 and the last half of the movement covers 210 to 240. Knowing this it's highly possible my actual temps the year before were possibly in line with what I saw last year as well.