Electric fan - radiator cooling

[sideshowbob]

I have an '88 635 CSi. In normal running it has no cooling issues at all with the temperature guage running slightly to the left of the mid point on the temperature guage.
However if caught in a queue , particularly on a hot day the guage moves over to the right as the engine temperature increases, at this point I tend to loose my nerve and open windows, sunroof and turn the heater and electric fan on. This is an attempt to prevent any potential boiling over.

My question is, normal engine cooling at slow speeds is via the viscous fan and additional cooling is via the electric fan, however I am not sure whetherv or not my electric fan is working. How can I test the functionality and when working what is its operational temperature range ?

[Brucey]

if you unplug the wires from the sensor (which I think is on the RHS of the radiator and has three wires on your car; earlier ones are different) you can connect the wires using a jumper and the fan should work at both speeds. Alternatively you can put a jumper in place of the relay (s) and test the fan that way. It is not uncommon for the later style of fan (non-Bosch) to fail. I've had at least two clap out on me and I have sourced the earlier Bosch fan (which is noisier) instead. The electric fan should also operate at low speed when the AC is engaged. Sometimes the fan fails on low speed only (e.g. because the ballast resistor fails).

However testing the sensor itself is more difficult; probably the best test is to remove it and sit it in a pan of hot water; IIRC the high fan speed cuts in at 99C. These sensors are not very reliable; I think the one in my car is not working properly.

The viscous fan is only just adequate to cool the engine if you have been cruising and have to pull up on a hot day. Often the viscous fan goes bad and it isn't noticed for a long time. Running the AC and the PAS pump uses quite a lot of fuel and makes quite a lot of heat, so sitting in traffic risks overheating anyway. If you are caught out and think the cooling system isn't working properly, it is OK to drive slowly with the bonnet unlatched/propped open and the extra airflow through the engine bay helps cool the engine. It does however risk engine fume from entering the cabin via the air intakes.

A good modification is to fit a manual override switch to the electric fan controls; this allows you to nip any overheating in the bud.

cheers

[sideshowbob]

Thanks Brucey....I like the idea of the manual over-ride switch, gives s bit of reassurance if you are stuck in traffic on a hot summers day. Thanks.