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My 300 EXC doesnt like keeping its coolant ??

7K views 32 replies 12 participants last post by  Scriberman 
#1 ·
My 2007 300 EXC doesnt seem keen on hanging on to its coolant...

It seems to overheat a bit to easily, normal riding is ok but a bit a gnarly hill climb and thats it steam all over the place and bugger all coolant left.

I suspected a knackered rad cap, so I replaced that.

The old one must have fukked cos as soon as it presurised it starting leaking all over the place.

Fixed the leaks, but it still seems to overheat and dump the lot.

Any ideas ??
 
#5 ·
i had overheating problems once. cured by fitting new cap (you can get a high pressure one) and using a 50% coolant mix.

if you replaced the cap already then what mix of coolant are you using?

i also fitted a long hose to get rid of any overflows so it doesn't steam up goggles if it does go fizz
 
#9 ·
well if you have a 1.8 bar cap on, and good quality fluid i'd say the next place to start looking is the thermostate and then the pump. daft question but the rads/engine has been bled of air?
 
#11 ·
might not be relevant, but I has the same problems on my 530 exc, fitted a fan and better but not fixed, then I looked at the pipe that comes out of the bottom of the radiator and it had been squashed very oval in an "off" it was restricting the coolant flow, once quezzed carefully back into round and the rads could flow properly all good, so I would check your rads over carefully and also your rubber pipes in case they have collapsed, almost certainly sounds like you have either a blown head gasket or a blockage somewhere, it is was head gasket I would expect the coolant to end up in your gearbox oil, have you checked that? Any mayo?
 
#14 ·
So heres a thought....

Stripped it all down tonight, tested the thermostat which opened at about 55/60 c

But... feck me thats a huge restriction even when its fully open.

So I'm ditching that.... which I assume means I can ditch number 24 from the diagram and block off the outlets.

Anybody know if that'll work ok ?

Auto part Diagram Font Automotive engine part
 
#15 ·
Hmmm this still isnt fixed :hmh:

So far:
Re-routed rad pipes so not squashed
Ditched thermostat
Cleaned all fins on the rads
Replaced rad cap
Filled with 50/50 halfords best anti freeze & water.

Still boils up on mediocre hill climbs :mad:

Whats next to try then chaps :confused:
 
#16 ·
After it has boiled then cooled down, is the water still above the fins inside the radiator? Many people put too much coolant in the system and it boils off the excess then its OK. Should be just above the fins when cold.
 
#17 ·
You say the fins are clean but can you see clean through the radiators from one side to the other? They can look clean but not be when you look close. It makes a massive difference to the cooling, even if 25% is blocked to the air thats 25% less cooling, good for making tea but not good for motors.
 
#22 ·
Get waterless Coolant !! Made by Evans. £30 for 2 litres.

You dont need a fan or high bar rad cap. It boils at 180 degree & freezes at -40 !! Also it wont corrode the rad either.

Ive had it in my crf 280x & its in my 300 exc with Rekluse. I do a lap of Cown quarry & whip off the rad cap & nothing - no steam - or boil overs !!! STICK IT IN & FORGET ABOUT IT
 
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