FC Thermoswitch in 108 degree weather
 

I have a fairly stock FD with only reliability upgrades and modifications, and today reached 108 degrees here in Sacramento and I must say that I am impressed at my engine temps.

Everything is stock : radiator, intercooler, engine, stock converters, only cooling mod is the fc thermoswitch and aluminum ast. I didn't even realize that it was that hot outside, but I realized in traffic my coolant temps reached 220 max which was a little warmer then my usual but still considered normal, but when I realized it was about 108 degrees outside, I realized that's not bad!
I ran the car hard for several hours in the extreme heat testing my boost not realizing how hot it was and the coolant temps on average stayed at about 190-205 degrees with hard driving, then the cooling fan stays on for 10 minutes to cool the engine while the car is shut off.

I would strongly recommend every FD owner with a fairly stock FD who wants to slightly upgrade the cooling system without performing extensive and expensive modifications, get a FC Thermoswitch. Totally worth it :)

BTW it was so hot today my temp gauge was reading 140 degrees after the car had been sitting for 8 hours :shocking:

The fan speeds are increased in steps.

On a stock ECU, the FC thermoswitch will turn the fans on at 207F/97C and keep them on until they drop down to 194F/90C. Then the ECU will speed the fans up at 105C/221F. The A/C will also increase fan speeds independent of coolant temperature. These are pretty much the same trigger temperatures that the Rx-8 uses from the factory.

If you had a stock FD thermoswitch, the ECU would first turn the fans on at 105C/220F. Then the FD thermoswitch will speed them up at 108C/227F. The A/C will also increase fan speeds independent of coolant temperature.

If you have a Power FC you can change the temperature at which the ECU triggers the fans. But that only controls one "step" of fan speed. The other two "steps" are independent of the computer. So the FC thermoswitch is a valuable mod on both the stock computer and the Power FC. The thermoswitch is also used to trigger the aftercool function in the cooling fan control module, so with the FC thermoswitch your fans may be more likely to stay on for a 10 minute period after you shut the car down.

Good to know.

When I first found out the FD fans didn't come on till 221 F I was shocked. That is ridiculous!

Hmmm that might explain why the temps didnt go any higher then 220. Thanks, I learn something new everyday!

Some domestics run that hot, you'd be surprised. A lot of BMW's do too.

Yea, Mercedes V12's definitely do. Used to work as a Benz tech. And they're just as problematic as FD's and cost 4 times as much to fix!

I agree, the FD stock cooling system is not THAT bad.

I have a stock radiator with a FMIC and i have never seen outrageous temps.

Just recently was i caught in a one hour DEAD stop traffic jam in 95 degree weather. It literally took me 1 hour to travel 2 miles. They completely blocked off the turnpike and everyone had to make the same exit lol

I was very surprised at how my temps steadied.

Of course i had my fans running the entire time but still, it never went past 205F. And i had already been driving 45 minutes prior to that. So almost 2 hours total in 95 degree weather and my temps never went above 205F, with the stock rad and a FMIC.

And yeah there are times when my car has sat for days and i go start it up in this hot weather and temp shows like 120F already lol. But i still warm it up though lol.

So...was this with the A/C on or off? My car is currently in pieces 'cause I'm installing the FC thermoswitch and a new thermostat. I'm hoping the thermoswitch will keep my temperatures under 100C when I'm running the A/C. Currently, with the A/C on, my temperatures will ever so slowly creep up to 100 and beyond...and I already have a PowerFC which is set to add a speed at 95C.

The FC thermoswitch is one of the best 'reliability' mods you can do for your FD.
Everyone should do it.

Recently (at ~102 K miles) took the forum advice and installed the FC thermoswitch. Most noticeable effect on this near-stock '94 is the increased frequency of fans running after shutoff. Wife is worried about shortened battery life. I checked battery voltage just after the fans shut down; measured 12.45 volts across battery terminals. Fully charged, the battery sits at about 12.6 volts; I can't see the fan current drain as a future battery problem. Any opinions on this?

The heat from the engine bay will likely do the battery in before a little bit of extra fan runtime here and there. Also, keep in mind that the fans are running on low speed....not much amp draw.

For anyone in NZ - I just bought a FC Thermoswitch PN41-18-840 from John Andrew Ford/Mazda yesterday for $70NZD. Easy to get, but needs to be shipped in from Japan.

I too have the FC switch. One additional thing that I did during installation was to splice in an additional length of wire--a loop up to the air pump area--with a switch in series. The purpose of this is to be able to defeat the thermoswitch and allow the temps to come up to higher levels to assist in passing emissions tests (and/or for cold weather operation, if you need more heat).

Our '94 passed emissions easily this year, with the FC switch installed.

I covered this in my thread: https://www.rx7club.com/3rd-generation-specific-1993-2002-16/why-engine-so-damn-complicated-part-3-cooling-fan-controls-876767/ On the FD it works like this:

https://www.rx7club.com/attachment.p...1&d=1260067160

Here is where the fan control module and the multi-speed fan control system are truly advantegous. The fans run for 10 minutes max due to a timer in the cooling fan control module. The fans are also throttled down in speed. When aftercool begins, the fans run at medium speed. Once the thermoswitch cuts off (temps drop enough) the fans slow down to low speed until the 10 minute timer expires. The system was engineered well enough to prevent a major battery drain on a car with a healthy electrical system. That being said, running the fans after shutdown certainly doesn't do the battery any favors. But one of the reasons Mazda put the fan control module in was to keep the engine bay from getting so hot that hoses would start to bake. FYI the Rx-8 also has an aftercool system that can be triggered by an engine bay temperature sensor:

https://www.rx7club.com/attachment.p...1&d=1260111471

Anecdotally, some 2nd gen cars with electric fan conversions run off a thermoswitch only and have no timer circuit. So the fan will run continuously (usually a single speed fan) until the temps drop without any throttling or timer circuit. I haven't heard of any battery drain problems occuring even in those kinds of setups.

For anyone that has a garage:

Always open the hood when you park the car. This will allow the engine to cool much faster, and will limit the amount of "cooking" that you will do to all of the under hood plastics and other components. ALWAYS!!!!

I performed the same test myself. I turned my car off and the fans continued to run for 10 minutes. After the fans shut off, I checked my battery voltage: 12.75 volts The FC Thermoswitch will NOT drain your battery.

I dont have a/c LOL! However I had the interior fan running on full blast to try and stay cool.

I found a thread a while back that AdamC mentioned that he passed smog with his engine running at only 180 degrees, and a good catalytic converter, so I don't believe the FC Thermoswitch will affect emissions.

Oh yea it can [affect emissions].

If you are right at the limit, like I am, building all the heat you can will generally improve your chances of passing the tests. Even with a good cat, airpump, ignition, tune and all the emissions controls, etc., my large ported /high overlap motor just squeeked by the CA emissions tests--but only after getting the temps way up.

I grant you this will be less of a concern for a stocker or near-stocker and those with less aggressive porting setups, etc..

i am going to FC thermoswitch, this mod sounds great but.. have you any manual for this switiching? or some photo document.
iam greener with this... :blush:

Metan, DaleClark has already made a thread about that.

I'm about to get a FC-switch and do this mod. I also have a stock ECU. But looking at the wiring diagram makes me wounder if the fans really will come on at 97C.
https://www.rx7club.com/attachment.p...1&d=1282925729
The thermoswitch just adds another grounding point to the fans, there will be no voltage at the fans, thereby no rotation. So an FC-switch with stock ECU should give the following operation,
https://www.rx7club.com/attachment.p...1&d=1282925729
Those who tried, am I right?

I'm thinking about rewiring the relays to recover the stock way of operation. But I don't understand why the ECU needs to control TWO relays??

No pics, but see post #54 in this forum thread.

Also regarding emissions tests with FC thermoswitch installed, here is one data point from our '94:

Post #29 in this thread. :icon_tup:

The "Fan Thermoswitch" as referred to in these posts is not the "Thermoswitch" in your diagram (that's for the A/C system); it is the "Engine Coolant Temperature Switch." Closing that switch grounds the return path for the control coil of the #3 cooling fan relay, enabling the terminal "D" ground returns for the two cooling fan motor coils, and also grounds terminal "C" of the Cooling Fan Control Module, which was added by the fuel recall. The result is that terminal "E" of the control module now controls the "B" terminals of Cooling Fan Relays #2 and #4, and if it pulls them low, this will power up the terminals "B" of the fan motors. Unfortunately I don't know what's inside the fan control module, but before it was added, the fans could not run after the ignition was off, and after adding it the fans can and frequently do run with ignition off. Whether for a certain time, or whether until the "Engine Coolant Temperature Switch opens, I don't know.

After installing the FC switch on our '94, the after-switch-off fan running time has not changed much, but the fans operate in that mode much more frequently than during the previous mileage (102K miles) on the FD switch.

The reason why I know for a fact that the fans do come on at 207F or 97C, is because I put an aftermarket temp gauge and I let the car idle for about 30-45 minutes and watched my engine temp keep rising slowly, until the needle stopped rising around 205ishF and it didn't increase anymore. At that point I did hear the fans kick on.

I do that EVERY time I park in the garage! Good advice!

I also meant the "Engine Coolant Temperature Switch" when I said "thermoswitch".
Exactly, it just adds ground to the fan motor and two grounds shouldn't make the motor run.

But it seems to run for Ernesto13B, have to short my relay and observe.

Well damn!
I was about to call a tow truck when my temps got up to 226* after I swapped my (fc) thermo switch which comes on @ 207* w/ a subaru switch with a shorter element that supposedly comes on at 194 and off at 185. But apparently its ok to run that hot...

After installing the thermoswitch, the most drastic improvement was how much less flashburn you get on your face when you open the hood after a long drive ;)

The e-fans certainly do come on more frequently, especially the aftercool function. It happens everytime is shut down th car.

I'll take lower batter life for prolonged harness and plastic component life!

Yea what's harder to fix? Broken vacuum lines, crispy wires, blown engine OR a battery lol

The provision of ground to the return side of the fan motors' windings enables, i.e. allows the motor to run when its "B" terminal gets power. The fan motors' "B" terminals get power from the Fan Control Module via the relays #2 and #4 when the FCM's terminal "E" goes low, which is (probably) caused by its terminal "C" going low, which is what happens when the switch closes.

In other words, closing the switch turns on the fans. (This would not happen if the Fan Control Module was not present.)

Good info

I always pop the hood. I practiced this religiously since i first owned the car.

There has never been a time where i just shut the car off and left. Either i had the fans running for nearly 5 minutes after shutdown or the hood was popped. Sometimes even both depending on the driving and/or ambient temp.

You'd be amazed at how fast the temps rise when you shut down.

I once parked at a rest stop on the turnpike. It was about 85 degrees outside. Pretty warm but not bad. After i shutdown, i ran the fans for 2 minutes, just to bring temps down a bit to buy me time so when i come back, the temps arent insanely high lol

Ran fans til temp gauge read 185F. Shut car down, went inside rest stop and went to ATM. Got some cash and walked right out to the car. I'd say i literally took 3-4 minutes TOPS.

Got back in the car, turn key to ACC and temp gauge showed 215F LOL

I was like wtf? A 30 degree increase in like 4 minutes? Thats insane. I was driving for about 30 minutes prior to the rest stop with some boosting but still. I think thats still crazy.

So for the people who think popping the hood after each drive is a waste and stupid, think again.

Too bad there isn't a supplementary electric coolant pump at the water pump inlet that would run when ignition is off and fans are running.

Maybe we could mimic other manufacturers and incorporate it to work with the FD system.

When i had my audi tt, the water pump would run when the car was off. I dont remember how long, i think 5 minutes?

Id say this would be useful for people who daily drive the car and dont have the luxury and time to just sit in the car with the fans on or with the hood up. But even if they did that, they still have hot coolant just sitting anyway so...

I had the same idea after seeing the same electric pump on my TT...problem is, you'd need an extra nipple somewhere on the radiator to put the pump in an effective flow path. It would probably be easier to just ditch the stock belt driven pump and go to a large electric water pump.

Just FWI.. with my stock cooling system minus ast, fresh coolant, and fans set to turn on at 84c. My car would not pass 90c even in the hottest weather with normal driving.

Now with a V-mount, it dosent really pass 90c on the track during 95f weather. 104c or 220f seems kinda high for non-spirited driving conditions even at 108degrees ambient.

ArmenMAxx,

Why and how set the fans to come on at 84°C, when the thermostat is not even fully open at that temperature? Fully-open on the stock thermostat is 95°C. Why not let the water pump do the work until its capability is fully maxed out at 95°C, then set fans to come on just above that temperature. The FC fan thermoswitch closes at 97°C, which makes sense... to me, anyway.

I dont know when the thermostat is fully open, but I do know that the cooler the car runs the better and if my car holds 84c during track days with cooler ~80degree farenheit ambient temps, im happy. Setting the fans to 84c helped a lot and I recommend it to everyone (dosent have to be 84, I would recommend between 84-88c).

FYI, from the "Mazda RX-7 1994 Workshop Manual," page TD-4:

Opening temperature 80.5 - 83.5°C (177 - 182°F)
Full-open temperature 95°C (203°F)
Minimum full-open lift 8 - 10 mm (0.31 - 0.39")

Holding temps to 84°C by any means will severely restrict coolant flow, unless a lower temperature thermostat has been installed. (Maybe that's OK, but maybe not.)

Ah now I understand why the fans turn off at 203f.

Thanks!

Thermostats don't need to fully open in normal operation. They are intended to restrict the coolant flow through the radiator in order to hold the coolant temperature at or near the thermostat's opening temp. If you have proper--i.e., enough airflow and heat rejection capacity--then you temps should sit just above the opening temp and increase only slightly with additional load. (And based on my own experience, this is pretty much what happens with a properly ducted v-mount setup.)

Accordingly, the thermostat will regulate temps while the car is moving (with sufficient velocity to establish airflow) and the fan switch is intended to provide airflow while the vehicle is moving slowly or at rest.

The stock thermostat (and many normal temp stats) start to open at about 82 deg C. So, ArmenMaxx, you car at 84 deg is doing just what I would expect it to do.

Agreed, in fact I agree with all you wrote. My point was that firing up the fans at 84°C pretty much overrides the thermostatically-controlled coolant system. As you wrote, if the system is working properly, when the car is moving the coolant temps should not go above that set by some intermediate value of thermostat opening. (The Miata normally runs with its thermostat open about halfway.) Additional cooling from the fans is not needed unless coolant temp goes above 95°C.

I have a question. What does the FC thermoswitch trigger normally, since it does not come equipped with electronic fans?

Not familiar with the FC, but would guess that the signal from the FC's thermoswitch is sent to a fan relay coil, which responds by switching on the FC's fan(s?). Anyway, that's how it worked on the '90 - '93 Miata.

turbo and automatic FC's had a small auxiliary electric fan and a simple fan control module which relied on the thermoswitch. These engines have the thermostat housing tapped for the thermoswitch. Most cooling was still done by the clutch fan. 5 speed non turbo models didn't even have a thermoswitch or auxiliary fan and the thermostat housings were not tapped for the thermoswitch.

Thanks for the info boss. Very informative.

pffft, it hits 108 regularly here in the valley.. :)

Ok, I put the FC Thermoswitch to the ultimate test... SevenStock!!! My temps stayed around 180-190 during the entire 7 hour trip to Irvine, CA. On the Grapevine, with 90 degrees outside, my temps started slowly creeping to about 200's and I saw 210F, but I watched the gauge carefully, then temps started decreasing again rapidly back down to 180F, I'm very pleased with the thermoswitch!!

Ernesto13B, did your fans come on? If not, the FC thermoswitch did not affect your temps. My turbo'ed Miata's temperature did pretty much the same thing going southbound up the Grapevine, but I was doing an indicated 95 mph at the time. The Miata's fan also comes on at 207°F, but the drop in temp to 180°F was probably because of the lightened load on the engine once at the top, rather than the fan doing anything. If your fans did come on, then the FC thermoswitch definitely helped.

the thermoswitch will activate at 207F but stay on until temperatures drop below about 195F