My new bought used Montesa starts fan after few minutes of use even in cold weather, and fun works almost all the time. Could it be wrong thermo switch or something more serious? Previous owner has been riding her for two years but did not think of it as a problem.

Have you checked the fluid level ?

Yes, it's normal that the fan runs often.

 

Have you checked the fluid level ?

It seems OK. May be one of those special fluid, Engine Ice could help. Lean mixture can be the reason but I have no experience with EFI.

Yes, it's normal that the fan runs often.

I wonder how often it will be in summer.

Even more often. The time it's not running will be very short.

But I guess as long as it's not spitting out coolant, you're ok.

 

Maybe you could measure the time it's not running and compare it with someone else's 250 4RT, to put you at ease.

 

There's a reason why one recommends to install a larger radiator when using 280 or 300cc big bore kits. I've got one on my 300RR just to be sure.

Edited November 16, 20169 yr by guys

It seems OK. May be one of those special fluid, Engine Ice could help. Lean mixture can be the reason but I have no experience with EFI.

I run the Engine Ice and it seems to work well for me in summer time out near Boise Idaho.  My fan runs a bit more than my wife's Gas Gas, but not a lot more...

 

As for lean with the EFI... If your running one setup for the street with the O2 sensor or if you have a programmable TB with a custom map you could be running lean.  If that isn't the case then the likely hood your lean is slim.  

 

Even more often. The time it's not running will be very short.

But I guess as long as it's not spitting out coolant, you're ok.

 

Maybe you could measure the time it's not running and compare it with someone else's 250 4RT, to put you at ease.

 

There's a reason why one recommends to install a larger radiator when using 280 or 300cc big bore kits. I've got one on my 300RR just to be sure.

 

Well, my next question is predictable: where to by lager radiator? I saw it on www.Montesa4RT.nl but no details.

 

I run the Engine Ice and it seems to work well for me in summer time out near Boise Idaho.  My fan runs a bit more than my wife's Gas Gas, but not a lot more...

 

As for lean with the EFI... If your running one setup for the street with the O2 sensor or if you have a programmable TB with a custom map you could be running lean.  If that isn't the case  then the likely hood your lean is slim.  

It is Full Power Kit. I'll try with Engine Ice first, hoping for the best. Many thanks for both of you guys, I'm a little bit less worried now.

I bought mine here:

(scroll about 1/3 of the page down)

 

http://www.handdracing.co.uk/userimages/procart2.htm

 

But I've never heard of a 250 or 260 4RT with cooling problems, so the standard radiator should be fine when everything else is ok. .

Well, my next question is predictable: where to by lager radiator? I saw it on www.Montesa4RT.nl but no details.

 

It is Full Power Kit. I'll try with Engine Ice first, hoping for the best. Many thanks for both of you guys, I'm a little bit less worried now.

Thats what I figured. 

 

So it sounds like a flush and refill with the Engin Ice might help.  You might also run a tank of injector cleaner, double check the tea bag filter, and double check how clean the TB is, maybe fuel systems a bit restricted or your getting an inacuret air volume mesurement because of some build up in the TB?  (I doubt it but maybe?)

 

Good luck. 

Edited November 18, 20169 yr by jonnyc21

Thats what I figured. 

 

So it sounds like a flush and refill with the Engin Ice might help.  You might also run a tank of injector cleaner, double check the tea bag filter, and double check how clean the TB is, maybe fuel systems a bit restricted or your getting an inacuret air volume mesurement because of some build up in the TB?  (I doubt it but maybe?)

 

Good luck. 

Engine Ice did the job, fan is not running all the time any more which is acceptable for the time beeing (+15 Celsius outside).  Next step is tea bag filter, fortunately I've found out the meaning of it.   Hope you won't hear of me until next summer

I use Evans Waterless Coolant in all my bikes (http://www.evanscoolants.co.uk/Coolants/Performance/powersports). Don't think that it makes the fan run any less than normal coolant (don't know about Engine Ice) but it does have a much higher boiling point, so means if you overheat it won't boil over so loosing all the coolant.

 

Although not a problem with the Montesa, it won't corrode magnesium because it doesn't contain any water.