Radiator fan not on automatically

:
03 p5 92 miata
Recently noticed my cooling fan does not come on once the car gets up the running temperatures. If I hit the air conditioner button, both fans will come right on, but push the button again and they both go back off.

Is this simple as a faulty temperature sender switch? The temperature gauge needle still works appropriately, just won't kick the fan on when need be.
 

pcb

The Diagram Dude
:
2002 MP5
Your car may not have been hot enough to kick the fan on.

The temperature gauge on the dash is a dummy gauge and is kinda useless.

Some code readers will tell you the actual temperature that the ECU is reading.

There are two codes that you could throw if the ECU detects a problem with the ECT.





You can unplug the ECT and take a resistance reading of the sensor, without removing it.







There is a temperature test for the ECT if you remove it.









I remember one guy who's car wouldn't start when it was hot.

He removed and cleaned the sensor with sandpaper.
The sensor was coated with crap and giving inaccurate readings so the ECU wouldn't kick in the fuel pump for extra pressure for a hot start.
 

pcb

The Diagram Dude
:
2002 MP5
The fan isn't supposed to turn on until the car is quite hot.

You could just idle your car until the dash temperature gauge starts to rise above the halfway mark to see if the fan kicks in, but that's risky because, by the time your factory gauge starts rising above half, you're dangerously close to a warped head.
 
:
03 p5 92 miata
Nah the car was quite hot enough to trigger the fan. I plug my bluedriver obd2 in and monitor the temps and they will get into the 200s, fan still not kicking on.

This whole issue started when I parked my car after driving and heard some bubbling. Popped the hood and the reservior overflow was bubbling over. Got it hope and noticed the radiator cap had fallen apart. Replaced it and thermostat and I dont have that issue anymore, but the fan still not triggering itself even after a 30 minute drive bothers me.

I may rewire that single fan to turn on with the ignition and also throw a separate switch on it so I can turn it on right after the car starts.

Ill pull the sensor out though and give it a test like you linked in the photo. Thanks!
 
:
03 p5 92 miata
The fan isn't supposed to turn on until the car is quite hot.

You could just idle your car until the dash temperature gauge starts to rise above the halfway mark to see if the fan kicks in, but that's risky because, by the time your factory gauge starts rising above half, you're dangerously close to a warped head.
I checked the resistance of the sensor with it still in the car with coolant temps cooler and at running temp. Both values were within the range in the manual you posted
 

pcb

The Diagram Dude
:
2002 MP5
I may rewire that single fan to turn on with the ignition and also throw a separate switch on it so I can turn it on right after the car starts.

If it were me, I would wire the fan to be on whenever the car is running.

Other than wearing out your fan, I see no problem with it.

You could wire in a switch but you wouldn't want to forget to turn it on.
 

pcb

The Diagram Dude
:
2002 MP5
The only other thing that comes to mind is an airlock...

Make sure you bleed the system of any air.

Turn your heater on full.

 
:
03 p5 92 miata
If it were me, I would wire the fan to be on whenever the car is running.

Other than wearing out your fan, I see no problem with it.

You could wire in a switch but you wouldn't want to forget to turn it on.
This is my current plan. At the moment I am driving with the ac on most of the time to trigger both fans. I will wire up a switch to the fuse box to run one fan all the time when I am driving. Likely an illumnated switch which will remind me more easily when its on or off.

There is def no airlock. It is bled just the way it needs to be. Maybe for ha'has Ill order a new thermal switch to just throw in there since they are only a few dollars from rock auto.
 
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