What turns on the auxiliary fan?
 

1987 740 n/a

What turns on the auxiliary fan, the one at the very front of the car (in front of the condensor)? Is it solely the fan switch in the upper passenger corner of the radiator? If so, at what temp should it come on?

If that fan does not come on when the temp gauge climbs, should the switch then be suspect?

Thanks.

RE: What turns on the auxiliary fan?
 

I have a 91 740 turbo, and my aux fan comes on when it is very hot out and the car has been running for a while. Im not sure about your 87, but that my guess.

RE: What turns on the auxiliary fan?
 

The thermoswitch does control the fan. The temperature at which it does this is stamped on the body of the thermoswitch.

If it is suspect, partially drain the cooling system (to just below the level of the thermoswitch), disconnect the leads and unscrew it.

To test the switch connect a battery and test light across the terminals. Heat the switch in a pan of hot water. The switch should close (light on) at approximately the temperature stamped on it (thermometer required). As the switch cools the light should go out. If not, renew it.

When replacing the thermoswitch use sealant on the threads.

RE: What turns on the auxiliary fan?
 

The A/C mainly Works the Fan.

RE: What turns on the auxiliary fan?
 

Hmmm, but if the A/C works the fan, why is the thermoswitch in the radiator?

RE: What turns on the auxiliary fan?
 

That is there as a Back up for the coolant.

You also have a Manual clutch fan on the engine as well correct?

If that one goes bad the electric one will come on so the Car doesn't overheat.

I know this is an old thread..... however when removing auxiliary fan switch thermoswitch? is unit screwed into radiator or held in place by the rubber gasket that surrounds it, ie can it be pried out?
1991 740 n/a

Depends on which radiator you have.

fair enough. any identifying feature? safe to say there is (on some volvo rads )a switch that does not screw in and is pried out when doing rad replacement?