I've got an 04 rx8.
Recently noticed that when idling, the cooling fans don't work(i'm assuming they dont work at any other time either) and i get some vapor under the hood. The dash temp never moves from just below halfway-but if it's anything like my rx7, it prob doesn't budge until just b4 the engine's about to burn up.

Did a little research, tried moving the fans manually-they both turn ok.
Then tried jumpering the middle fan relay--1 of the fans turns on. Then I tried jumpering the left fan relay(while the middle relay is jumpered)--the 2nd fan comes on also.
So, it seems the fans are good and I assumed the relays were bad and replaced all 3 fan relays.
Still no fan at idle.
I'm assuming the fan relays get a signal from the ecu. Where does the ecu get signal from?
My coolant reservoir level sensor is shot, but that doesnt have anything to do with coolant temp, right?

Given the above, I would have to assume that maybe whatever sensor feeds temp to the ecu may be shot.

Am I on the right track?

For now, I setup an aftermarket relay to turn on 1 of the fans whenever the ignition is on.

 

I'm not sure my fans turn on in the winter either. The threshold is north of 190F. They could be unnecessary.

If you have an OBD2 reader, see what coolant temperature the ECU thinks it's getting. See of it's reasonable. There's 1 ECT sensor, its sort of under and to the outside of the thermostat.

 

Given where you are located, my guess is they haven't been needed in your current climate.

Stock mapping the fans don't start turning on until past 200 F.

 

Y, that's what I'd think too, but, for eg, on a 50 deg day, after a 30 minute drive to work on the hiway, I'll stop at a light on the offramp exit and after about 15 seconds, I'll notice a bit of steam coming from under the hood.
That prompted me to check the coolant overflow, which is losing coolant.

..but I'll see if I can find an obd2 reader that'll show engine temp.

 

Have the cooling system AND THE CAP pressure tested, and go from there.

 

Get an OBD2 scanner and check the temps. The stock fans turn on low speed at 206F and high speed at 213.8F. Turning on the AC will also force the fans on. That's a good way to check them.

 

Well, 1.5 months later..I've rebuilt the engine with new coolant seals, replaced the thermo sensor, coolant overflow bottle, radiator cap, and am using a cooling fan control kit along with an obd scanner to monitor the temps in real time.
Everything seems to be working fine now.
EZ fix!! :-(