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.