My Ossa 280i has always had a problem with overheating and uses normally 250ml of water every time I fill the petrol tank. Up the hill trails it would boil dry if I wasn't carrying 2-3 litres of water in my rucksack and replenishing about every 15 minutes.

In the SSDT it boiled out on long road sections and blew a cylinder head and melted the pump impellers etc. rebuilt by the factory and it still boils even after they flushed and refilled the cooling system.

Yes, the radiator is clean and I even blew it out with an air hose and pressure washed all the dust out.. The fan works well on the thermostat, comes on as I reach the end of the field about 200m from my house, fan wired the right way around.

When it starts boiling it will even blow out a little cold water before it steams... Someone else suggests fatter o rings in the cylinder head to stop cylinder pressure leaking into the water system. I am going to try this and am then going to consider putting larger plastic wings on to channel more air through the radiator...

Does anyone else have any experience of this? Should I consider a blockage somewhere in the system and try radiator cleaner or a dremel?

And just as I was getting a little less rubbish at riding!

Have you checked the Rad cap? Maybe the seal is bad. If the proper pressure isnt maintained, the solution will boil at a lower temp than it should. Im also going to assume that its pretty hot there. If so, you may want to try some of the waterless antifreeze products that claim better high temp performance. I say claim because I haven't tried them personally, but I know people who do and they say they make a difference .

you have a crack in the head near the back where the silencer is. remove head and look closely. cheers

Google 'Evans waterless coolant' a chemical alternative to using water. It has a much higher boiling point, and does not pressurize the coolant system at all..... the fan can be on and you can remove the rad cap!

Works well in our Ossa's.

The whole point of a pressurized system is to increase the boiling point so you don't lose coolant, you have a major problem in my opinion.

Is it blowing the water out of the the small pipe .Is the fan coming on and staying on if not check the wiring loom as it goes into the ecu .My ossa done this the brown wire that comes out the ecu the splits into two check that joint should be soldered.

Hi tomch

I had exactly the same issue. As borus has suggested, it is likely you have a crack in the cylinder head at the rear. very hard to see especially when cold as it is in the o-ring groove. Crack expands when hot so you can heat the head with a hot air gun if you like to help reveal it. Clean it thoroughly first and use magnification. I had mine replaced under warranty. Sorted. Never had a problem since and I ride in Queensland Australia, so yes, its hot here too. Good luck.

My mate had the same problem and head replaced under warranty .

Edited August 7, 201313 yr by fatbastard