pinkbike Posted June 6, 2008 Report Share Posted June 6, 2008 (edited) I have just started to have my radiator fan on all of the time. As soon as I start from cold it comes on and does not switch off. It has never happened before, but the only thing I have done since is top up the radiator. Do you think the rad sender has gone? Any ideas please? Edited June 6, 2008 by pinkbike Quote Link to comment Share on other sites More sharing options...
sectionone Posted June 6, 2008 Report Share Posted June 6, 2008 Cheapest solution is to put a toggle switch on the wire and turn the fan on after it warms up. During the summer in hot climates you can leave it on all the time. Quote Link to comment Share on other sites More sharing options...
pinkbike Posted June 6, 2008 Author Report Share Posted June 6, 2008 Thanks for the advice. But I would like to get to the cause of the problem. What if I was to let the bike get to normal running temperature then just unscrew the bleed screw a little to let some air/coolant out to try and take out any possible air locks, would that help do you think? I am just not sure if the recent top up has any coincidence. Quote Link to comment Share on other sites More sharing options...
betabonkers Posted June 6, 2008 Report Share Posted June 6, 2008 It happened to me, it was only the switch. Quote Link to comment Share on other sites More sharing options...
pinkbike Posted June 6, 2008 Author Report Share Posted June 6, 2008 The switch? Do you mean the sender in the radiator? Quote Link to comment Share on other sites More sharing options...
stevel Posted June 6, 2008 Report Share Posted June 6, 2008 From the symptoms you outline, it is almost certainly the thermostatic switch in the rad. It is obviously permanently closed or it wouldn't start the fan when the coolant is cold. nor would it close if it was operating in an air lock. One other possibility is that the switch terminals have been shorted together effectively by-passing the thermo switch hence causing the fan to run permanently. (Riders often do this when the switch fails in the open condition) If the terminals have been shorted, then the likelyhood is that the switch has failed previously and someone has shorted them out to avoid buying a new one Unless the terminals are shorted together, for what they cost I would suggest that you get a new switch & don't mess about with bodges- you can bet your life if you rely on a manual switch in the circuit, one day you will forget about it and at least spoil your day's riding or at worst cause an expensive (or possibly painful) problem Quote Link to comment Share on other sites More sharing options...
pinkbike Posted June 7, 2008 Author Report Share Posted June 7, 2008 The terminals have never been shorted before, and since the bikes last clean and coolant top up it has just started to stay on all of the time. I haven't ridden the bike since I have noticed this and this is why I suspected an air lock. It just seems odd that the switch has failed during a bike clean or coolant top up? Quote Link to comment Share on other sites More sharing options...
pinkbike Posted June 7, 2008 Author Report Share Posted June 7, 2008 I think I have narrowed it down to the radiator temperature sender. If I remove both wires the fan stops. If I short them then the fan starts. I measured continuity across the contacts of the sender and it is a closed circuit. This leads me to believe that the sender is not open and therefore not functioning. Thanks for your help guys. If anybody can confirm or has had the same problem, please feel free to reply. Quote Link to comment Share on other sites More sharing options...
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