Hmmm, another issue :-( My cooling fan isn't working and it's causing the coolant to overheat. I've had a good practice in the woods this morning and It's steaming and spitting out coolant from the overflow. Does anyone have any tips for fault diagnosis by any chance? Thanks in Advance...

Woops, sorry; I just found another thread but I had previously searched and didn't get a result:

Put the two thermostat wires together then start it up. If the fan spins it'll be the thermostat. If it doesn't it may be the fan, but try a test bulb to the thermostat supply wire first (better than a meter as it'll show if the supply has enough guts to run the fan).

 

I'll try this first

What a top tip! Such an easy test and it turns out it is the thermostat. Thanks to Sirdabalot for the tip :-)

Oh, just tested the thermostat with multimeter with a pan of heating water and it seems to be working perfectly. Water pump? Airlock?

Glad I didn't just buy a new one!

Well, tested pump and reassembled and it's working perfectly. Strange one, must have been an airlock I guess.

 Keep it hot wired until you figure it out. When the fan starts going bad it can be intermittent. Give it a push start with a finger.

Well to be honest it's always possible that it was the connection at the junction of the wires and pulling it and replugging it sorted it.It's working a treat now and I've just done an hour on it. Thanks for the advice though.

 

Glad you got yours fixed, for anyone else looking for advice,

 I recently had a similar problem, bike started steaming and spitting out coolant, fan wasn’t coming on, when I wiggled wires connecting to thermoswitch it woud work for a while then stop again, dirty spade connectors I thought so took them of and cleaned them up, no different. I then as you did put wires together, fan worked no problem.

Next I thought it must be the thermoswitch so I put it in pan of  hot water,  connected multimeter and it worked fine.

Must be wiring, I then tested wiring and plenty juice through that, I then did a lot of head scratching, Wiring’s fine, fan’s fine, thermoswich is fine, spade connectors are gleaming but when all together it’s not working properly, what next?    Try everything again  

This time when I was trying the thermoswich I noticed there was a wee bit of movement in one of the terminals, I put thermoswich in pan of water it clicked and I got a reading on multimeter, with multimeter still attached I moved the terminal the wee bit it would move (only about .5 of a mm) and got a much lower reading (I’m not exactly sure how ohms work but new the reading shouldn’t change). This must be why it worked when I wiggled wire connectors at first.

Based on this I bought a new thermoswitch of Ebay and problem solved, so check for movement on your thermoswitch pins

Hope this helps somebody

  Ricky

Edited April 24, 20179 yr by holamb

Hmm well, I may have spoken too soon actually. It stopped working again at the weekend. I too thought it must be either the connection at the thermostat end or the junction of the wires further back so I first wiggled and messed with the wires going into the thermostat but that didn't help. Luckily I'd taken a few tools with me including the allen key for the plastic cover over the wire connectors. I tried wiggling the wires there too but to no avail. So I pulled the connector and bridged the wires and sure enough it worked, as soon as I  then replugged the connector block it worked and continued to work perfectly. Like with yours, the connections seem absolutely fine; no dirt or corrosion at all, it's almost as though it needed a reboot! But surely this can't be the case, it's just a connection...or not a connection! I was thinking I might use a different connector block of a higher quality (or just solder and heat shrink!!).

Next time it stops working could you borrow a known working Thermoswitch from another beta owner just to rule it out or buy a new one (not the best or cheapest way to solve mechanical issues), mine was only £18.50 from ebay, if you're in the uk

 Ricky

One thing to consider is the current required to start the fan going is considerably more than the current required to keep it going. When the switch first closes you can get an inrush current to the fan above ten amps as the motor builds up a magnetic field in the windings. After the initial demand the operating current usually drops to less than an amp.

I know this because I worked on motor control chips for a bit but mostly because I was troubleshooting a fan and put it on a current limited power supply and it wouldn't start up until I cranked the amperage. The problem is usually the thermoswitch. If it is operating normally it will have resistance in the milliohms. As the switch ages the contacts can build up oxides and carbon and pits on the surfaces due to the initial arc when the switch closes. This can cause the switch to gradually start degrading so even when closed it can read several ohms. Doesn't seem like a problem except it will degrade to a point where the required inrush current can't be provided reliably. So maybe you're cranking along and the lighting coils are putting out full voltage, enough to overcome the contact resistance, and the fan starts. Or you're sitting in line at a section with the engine idling and the fan just can't get enough current to start.

Comes down to when is an on/off switch not an on/off switch. So yeah you may read the switch as turning on and off but check the on resistance and you may find it's sufficiently higher than a new switch. Just back of the envelope type of calculation, say your switch has got 5 Ohms of contact resistance and your lighting coil puts out 12 Volts. E = I x R (Volts = Current x Resistance) Assuming the inrush current looks like a dead short across the fan motor, which is pretty close to reality when starting, then I = E/R (Current = Volts / Resistance) Current = 12/5 or 2.4 Amps. If the motor needs an instantaneous 10 Amps to start then the lighting coils can't push enough current through the switch to get the fan spinning. Or there might be almost enough current and you end up with an intermittent failure like you have. Keep in mind that resistance in a connector or ground will cause the same symptoms.

So the practical takeaway is those few ohms that you normally just ignore on a meter are actually pretty significant when large currents are involved. Even for a very short period of time.

That's really interesting Dan and it could well be the problem. I did think I saw the fan attempting to start on one occasion but giving up. I'll take it out again and measure the resistance when it's switched. Unfortunately there are aren't any on ebay so it's the full price of over £40 to replace so I might as well make sure that it is faulty before I replace it.

Harry, Give this a try, I've got a problem with my fan coming on as well, and can reproduce it, but haven't dug in far enough to find the cause. Here's the scenario:

with the headlight switch in the on position, fan will not work. as soon as the headlight switch is pushed off, fan will come on as normal. lighting circuit interfering with the fan circuit, but how and why? try this with yours and see if there's an issue. And if anyone has any ideas as to my problem, I'm all ears.

I know guys in the IT business who have used computer cooling fan motors as (cheap) replacements in vehicle applications.