Losing coolant in very hot conditions.

[robbo]

On my recent trip to the Spa Classic and the Black Forest, there were two occasions when some coolant was lost via the header tank overflow. Both times on hot sunny days stuck in traffic and limited to low speeds. I'm hoping the culprit is the radiator cap which has been ordered. However, although the fan operates within a few minutes on tick over from start up, as it should, is there a way of easily proving it would come on via the thermo switch in high heat conditions.
I know the manual suggests testing the resistance of the thermo switch  in a pan of water at various temperatures, but wondered if there's a simpler way.

[tex]

Take it for a ride so it' warm , then pull over leave the engine running the fan should come on at 99 degrees. 

[robbo]

Hi Tex,
Thanks for your reply. Is there some documentation that would list the operating temp to switch on/off the fan as well as illuminate the high temp warning light. On the US forum someone quoted 230f to turn it on 215f to switch it off and 260f to illuminate the warning light.
99°c does seem more like it. The downside if it fails to come on is melted fan blades or worse .

[tex]

Not sure about the light robbo , I'll have a look at the haynes later, I have the multi gauge fitted which displays the temperature and the fan always kicks in at 99 .you can fit a manual switch I think , on the yank site

[robbo]

Does the fan come on quite regularly in hot conditions. I get the impression it doesn't much on the 600's.  Without doubt a temperature gauge beats a light all day long, that's for sure.

[tex]

Hi robbo, yes in slow traffic the fan does come on a fair bit, especially when stationery

[robbo]

Tex,
Should get the new rad cap tomorrow. The weather will obviously be hot enough to give it a work out. If  the fan doesn't come on and it starts dropping coolant, then the thermo switch is the problem. Thinking about it, the last time I changed the coolant I was surprised it started to drain as soon as I removed the drain bolt. Normally very little comes out until the rad cap has been released, which does point to the rad cap not holding pressure.
Thanks for your replies.  [size=78%]I'll keep you posted.[/size]

[Hugh Mungus]

Unless you have an air bubble in the system.
I changed the coolant on my FJR and it seemed fine. Got stuck in traffic and it spat coolant out via the expansion bottle cos the fan didn't kick in. I suspected the fan but it was an air lock in the system. When you re-fill the radiator rock the bike side to side to help get air bubbles out.
Yes it could still be the fan so don't rule it out completely.

[robbo]

Fitted the replacement rad cap and went for a ride this afternoon. Deliberately stayed in heavy traffic in quite warm temperatures and after leaving on tickover in a carpark, saw the fan kick in and no loss of coolant.
Looks as though the rad cap was the culprit although couldn't see the hallmark for my £30.25. I could have got a copy for around a tenner, but glad the problem is sorted. Should get a proper workout on Friday as off to Cornwall for a music/beer/camping weekend. Thanks for all your suggestions. Hopefully all sorted.