Hey everyone,

I crashed my bike last year, and there was a small crack in the upper radiator. Right at the 'neck' where you refill.
This was welded, and after a first run I saw it didn't leak there anymore, but there was some leaking at the cap.
Bought a new cap, and there's no more leaking on the radiator.

But my bike is overheating. When I ride slowly, it's ok. But once I start hitting the gas, the temperature goes up. The fans are on all the time. Its sitting only a few mm from red...
When I got home, I heard bubbling in the overflow bottle and it was loosing a lot of coolant...

Checked the thermostat, works perfectly. Also looked at the pump, looks like new...
Had some dirt in the lower rad, it's in a bucket right now. But it wasn't very much, and it didn't ran this hot before my crash.. :/

Anyone got an idea what else it might be?

Another odd thing is that when I let it idle, the temp goes up, even up way in the red. When I rev the bike, it goes back.
I trust the temperature that it shows when revved is the right one?

Thanks in advance

sounds like maybe a blocked rad internally maybe. have you tried flushing fresh water from a hose pipe though the entire engine cooling system? or try running without the thermostat fitted?

I'll be trying both those options soon! Will keep you updated.

Though before my crash, my nc never overheated... So don't think it is blocked internally.

Well, it's not rocket science. There are three possible causes I can think of:

• the radiator isn't able to get rid of the heat (fins blocked externally)
• the hot water isn't getting from the engine to the radiator (internal blockage, thermostat stuck closed, or bad pump)
• water isn't getting to the engine (air in the system)

If you open up the filler cap (cold) and start the engine, you should be able to see that the water is pumped through, even with a closed thermostat. If water is pumped, the pump is working. You can check that the rad isn't blocked internally by blowing through it. I assume you've checked that the fins aren't completely full of crud and that you bled the air out of the system when you refilled it. Not many things left.

Since work was done to the radiator, one has to suspect that that's what's causing it...

Yup, sounds like air in the system.

Allright, got an update:

So after I checked the pump and the thermostat, which both worked correctly, I took off the lower radiator. Cleaned thad, now I can see through pretty much everywhere.
Put it on, did a refill. Bled the system following a guide I found in this forum (fill, let it warm up while squizing the tubes, rev it a few times, let it cool down and top off)
Took her for a spin. Drove about 25 minutes, temperature was nice around 90, a little bit above. Stopped, no coolant boiling. Happy! I put the fan on when she got at 90
Drove on for another 15minutes in which I saw the temperature rising... Came halfway between 90 and red. When I came home, the coolant was boiling...
She wasn't pissing any coolant though.

I ran out of idea's... Anyone here got any options?

Halfway between 90 and red with an original rad in the heatwave we are having at the moment?

I'd say that's not bad at all.

I have new chinese rads, new thermostat, silicone hoses and a HRC overflow and my bike is constantly between 90 and red at the moment.

Balls don't half sweat coming home from work.......

But why would my coolant still boil?

Well I don't have an exact idea other than, these bikes run hot regardless, it's bloody warm here at the moment, and you still have original rads.

Plus I bet when you got home you'd been below 40 for a while before you stopped? Or were at least stopping in traffic/at junctions more often.

Two other guesses:

1) Radiator cap is old / is not keeping enough pressure (usually a cooling system keeps its pressure so that boiling point is slightly beyond 100 degrees

2) There is another leak somewhere which is boiling the water off so you are not seeing it but its doing the same as 1 above.