Hello, hoping one of you wise ones will have a few ideas (just in case it ever stops raining)
After putting the 3TJ back together and running it up to temp with no issues I thought everything would be plain sailing.
But....whilst stopping for a nicotine fix after quite a long run I noticed loads of water/coolant not only coming from my expansion overflow pipe but from the bottle itself (had blown the rubber bung off). Got home ok but can't figure out how to make it stop doing this.

I've swapped the thermostat for starters. When I put the old one in boiling water I couldn't see anything happening. I also couldn't see anything happening with the brand new one either but the bloke in the shop said it has to be at the right pressure aswell - is this correct?

I've got all the panels off but when I put more water in and run it up it gets rid of loads of air bubbles and before the fan kicks in turns the shed in to a sauna.

Am I missing some really obvious bleed nipples anywhere? Its an import so I can't find a matching cooling system diagram on the web. There seems to be a bleed nut (8mm) on the outside of the water pump but as this is lower than both the rad and the expansion bottle I'm not sure what its there for.

The water isn't oily and theres no water coming from the exhaust so hopefully that rules out the head gasket. All the hoses seem tightly clipped and in decent condition - I can't see where its dragging this amount of air in from. I've used about ten quids worth of fuel running it up and getting rid of air bubbles with no end in sight.

Any ideas?

Lets start with the basics
is there a hose leaking
is the coolant cap working ok ... if it's not pressurising the system then it will boil.

Or it could be the water pump

check all hose clamps are tight and change radiator cap, and have right amount of coolant in expansion bottle.

I've put a new rubber in the rad cap - its as tight as can be. I've put dye in the rad - not much joy there either cos it pissed out 'old faithful' style when it blew the expansion bottle stopper off. All hose clips seem to be tight.

Just can't understand where all the air is coming from. I've seen big air locks in cars but never anything like this in a bike. Can't help thinking I'm missing something stupidly obvious. What do you think of the thermostat in boiling water not reacting and do you know what the 'bleed nut' on the water pump is for?

nut on pump is same as the two on cylinder barrells either side of 1 and 4 exhaust pipe, these are drain plugs, and need to be tight with copper orings, also change the rubber orings on all metal water pipes on the engine. ie the one from the water pump to thermostat metal pipe, and the two above.

if after this, consider a cracked cyclinder barrells or cylinder head.

hope this helps

Leave the thermostat out see what happens. if it still does it check the pump.

Taking the thermostat out didn't change anything so I got another rad cap from a breakers. The bloke there confirmed what you guys were saying. He'd worked for Yamaha and was forever replacing rad caps - something to do with the spring inside them. Even though I'd put another rubber in there it still wasn't doing the job.

Anyway, after draining and running up and getting rid of more air it finally calmed down. Under his instruction I didn't add any more coolant to replace that which got spat out whilst running up to temp. This means that when cold, nothing shows in the expansion bottle and it sits mid mark when running. Off for a long ride tomorrow so hopefully that will be the end of it.

Thanks again for the input.

... ... cool .... ....

I don't think the new rad cap worked. When I stop the bike after a decent ride I'm getting steam and coolant spatter from the overflow pipe and it sounds like a kettle boiling under the tail pod.

Its been drained and refilled without any joy - what would a garage do? Do they have any simple (cheap) way of telling if the head/cylinder is cracked?

Its quite hard to get my fan to kick in - it does eventually but only when the temp needle is past the screw (about 2mm from the red). Is this normal as it would certainly help if it came on sooner.

Thanks in advance

Is there any emulsification in the oil - any brown scum in it's oil filler cap ???

Is the crank case breather open - take the pipe of and check it's not blocked

But I'd say it's probably the head / base gasket