mr brightside
New member
A while ago now there was a thread about the cooling fan on a blokes car running of its own accord and i don't know if a cause was ever found. Yesterday i woke up to a flat battery due to the fan thing and i've found the cause if anyone's interested.
The fan circuit is enabled by a relay which closes a contact when the ignition is on, the same contact is also in parallel with a resistor which enables the fan to run slowly and silently with the ingition off. In the case of an intermittent fault with the fan temp switch like i had when the contacts fail to open after running the fan, you turn off the engine and think the fan's off too due to the loss of sound but it keeps turning away quietly and flattens your battery. After fitting a charged battery the fan did not start up again which was curious and made the problem all the more undetectable.
After having my arm devoured by the timing belt cover fitting the new switch [why did they stash it away under there] i'm supremely confident it won't happen again and thought i'd share the knowledge, which is power of course, to those who didn't know.
The fan circuit is enabled by a relay which closes a contact when the ignition is on, the same contact is also in parallel with a resistor which enables the fan to run slowly and silently with the ingition off. In the case of an intermittent fault with the fan temp switch like i had when the contacts fail to open after running the fan, you turn off the engine and think the fan's off too due to the loss of sound but it keeps turning away quietly and flattens your battery. After fitting a charged battery the fan did not start up again which was curious and made the problem all the more undetectable.
After having my arm devoured by the timing belt cover fitting the new switch [why did they stash it away under there] i'm supremely confident it won't happen again and thought i'd share the knowledge, which is power of course, to those who didn't know.
