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Discussion Starter #1
Hello. Have a somewhat odd problem with my 1990 C900.


After not using it these ppast few months, started it today and the radiator cooling fan came on after just a couple of minutes although the engine was still cold.


Then it remained on after I switched the engine off - still cold - and took key out.


After a few minutes I pulled one of the the radiator temp sensor connection to make it stop—which it did—only for it to come right back to life when I reconnected the temp sensor.


Switched the relay in the fuse box but no change.


The only way to have the radiator cooling fan off is to break the circuit either by disconnecting the fan engine or the radiator temp sensor.


Did a pin continuity test on the disconnected radiator temp sensor with multimeter and it comes back as open circuit when cold—which is as it should be, I believe. Yet, the radiator fan starts again the moment it is reconnected.


Any idea/advice would be much appreciated.
 

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Do you have AC?
If yes, your issue lies with AC.
 

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I recall some bad A/C relays did that, feeding back through the auxiliary fan or timer. Don't recall exactly.
 

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Check continuity on the fan switch... it is has continuity when the engine is cold, it has failed. It's a weird failure condition, but I have seen it before. Usually it's the AC relay, as noted.
 

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Discussion Starter #6
Well—what do you know—all of a sudden the thing has decided to behave.
The fan comes on once the temp neeedle is about a quarter of the way up from cold and then switches itself on and off as the car is left idling. It carried on going for about 90secs after I switched the ignition off and then stopped as it used to.


No idea what's going on, but guess I better get a new radiator temp sensor as this one may just have given a warning that it may be going south.


Will check things again latter or tomorrow. Thanks.
 

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You might check the gauge sender and thermostat... sounds like the car is running pretty cold, which isn't healthy for the engine.
 

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Discussion Starter #8
Had another go and the the radiator temperature fan switch still operates as described above.


Not sure what to make of «sounds like the car is running pretty cold» in relation to faulty/temperamental radiator fan switch, though?
 
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