Bike boiling over . . perhaps ?? (350 excf)

newbuild100

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Folks.
Towards the end of last year, I had real problems with my bike cooking itself. Having thrown money (and testing/checking) rad cap/therrmostat/thermoswitch etc I eventually traced the problem to a minute hole in one of the hoses. The bike has been great since.
However, today in a 3 hour (and very sticky) race, Im pretty sure the bike boiled itself again (Bit of steam and that sickly smell !!). I coaxed the bike back to the pits riding if for a few minutes at a time, and then pulling off the track (Fan running at this point so at least i know the fan switch/fuse is ok etc)

Having got home tonight, I undid the rad cap expecting to see a drop in coolant level but its to the correct level !!

Hows thats then. ? Either it didnt actually boil (and I just ran thru something. There was a lot of crap/water/slop about) . . or something else is happening with the bike.
Any clues anyone ?
Can these things be pressure tested at all ??
Thanks in advance
 
You leave us shooting in the dark somewhat; after all you were there.

If you are certain the engine overheated, I can only think the thermostat stuck closed for a while, so the engine temp rose rapidly until you intervened. You don't mention it but, presumably, the coolant pump impeller checked out last time, the whole system was flushed thoroughly & new coolant used, including careful burping to avoid any airlocks. Of course the system can be pressure tested, if you have access to the appropriate kit, but I think it would have simply blown it's coolant if there was a leak or failing head gasket..
 
Yes,last time,I went thru the system with a fine tooth comb.
No I’m not certain it overheated, but it did give signs of doing just that. What’s thrown me is the correct level of coolant now it’s cooled down. I’d have thought even if I’d shut the engine down immediately after seeing/smelling the signs, I would have lost at least some fluid ???!!!!!
 
My 450exc boiled on me during a race two weeks ago. I was stuck in a very boggy wooded section. This was the second time I’d encountered the issue in 5 years. Both times I had been in sticky mud and have put it down to overworking the engine and it’s limited cooling ability,combined with excessive mud around the engine and rad’s.

Keep it moving and all should be fine. I’ve never lost coolant much like you.


Sent from my iPhone using Tapatalk
 
Have you bled the air out of the bleed valve?
 
The cooling system is good for its job 95% of the time. The other 5%, when you are stuck in a bog, rads all clogged with mud, and you aren't moving fast enough to produce an airflow where the fan isn't blowing, it will overheat. Let it cool, clean as much crap from the rad guards as possible, and get it moving. Shouldn't cause a problem.
Mark
 
They overheat very quickly.

They are designed to be kept moving or if your stopped then stop and restart (that’s why they have a leccy start)

Remember they don’t have a fan out of the box, and will quite happily overheat if left to tick over for a minute or two.

Getting stuck in the mud is a recipe for it. Just do everything you can to ensure your cooling system is tip top.

Some people like the waterless coolant as it can take more before it boils.


Sent from my iPhone using Tapatalk
 
Thanks for all your answers guys. One more thing. Why are the fans designed to come on very late (ie near boiling point. The Thermoswitch on mine is 95 degrees). In thoery, would it be better if the fan could cut in earlier (ie cooler)

Thanks again guys, appreciated
 
Why not fit a little manual fan switch. Ultra easy.

Then if you get stuck and you feel it’s getting hot just bang it on til your moving again.




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Possible down side is can your battery take it?
I have a lower temp thermo switch fitted to my 950 and the fans are on virtually all the time.
Best bet as suggested to fit an over ride on/off switch :)
 
Greg, you did well to find that,I couldn’t find anything other that the ktm one.
Is there a downside to fitting a switch that cuts the fan in earlier ???
Thank you

Possible down side is can your battery take it?
I have a lower temp thermo switch fitted to my 950 and the fans are on virtually all the time.
Best bet as suggested to fit an over ride on/off switch :)

Choices:

Stock:

On at 100ºC, Off at 93ºC(?)


Coldest:

https://www.carbuildersolutions.com/uk/fan-switch-87c82c-m14-x-15-brass

On at 87ºC, Off at 82ºC


Middle ground - this one:

https://www.carbuildersolutions.com/uk/fan-switch-97c85c-m14-x-15-brass

On at 97ºC, Off at 85ºC


Or manual override.



I researched this supplier when I flattened the battery on my Husaberg on a tricky trail in Andalucia. Stalled near the top, I couldn't restart the b'tard until Tim came along with his size 13 boot and kicked it into life again!

:D
 
I researched this supplier when I flattened the battery on my Husaberg on a tricky trail in Andalucia. Stalled near the top, I couldn't restart the b'tard until Tim came along with his size 13 boot and kicked it into life again!

:D

I did feel for you, even gave you a Jelly baby to make the world a wonderful place again :comfort:D
 
Choices:

Stock:

On at 100ºC, Off at 93ºC(?)


Coldest:

https://www.carbuildersolutions.com/uk/fan-switch-87c82c-m14-x-15-brass

On at 87ºC, Off at 82ºC


Middle ground - this one:

https://www.carbuildersolutions.com/uk/fan-switch-97c85c-m14-x-15-brass

On at 97ºC, Off at 85ºC


Or manual override.



I researched this supplier when I flattened the battery on my Husaberg on a tricky trail in Andalucia. Stalled near the top, I couldn't restart the b'tard until Tim came along with his size 13 boot and kicked it into life again!

:D

Guys, is it easty enough to convert the fan i have fitted to use it manual mode, or am i buying a compete new fan kit altogether ??
 
Guys, is it easty enough to convert the fan i have fitted to use it manual mode, or am i buying a compete new fan kit altogether ??

Simplest way is to is to tap into both wires at the thermo switch ( the one screwed into the lower part of the radiator) and connect them to either side of a switch.
 


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