Coolant boiling

Hi All, just bought a thundercat as a toy now that my fzr is in bits and my triumph is still off the road. Anyway just got it home and left it running for a bit. The temp gauge has sat between 60 - 80 all the way, only rising to 80 at traffic lights although it did smell hot at a standstill. Once home the temp rose to 80 and coolant started gushing out an overflow pipe and could be heard boiling in the expansion tank. Once it cooled i checked the level and could see nothing in the tank although it only took a small amount to top up. I have taken it out again since and it has done the same but it has not cooled yet so i have not checked the coolant level. All the while the temp gauge has not risen above 80.
Any ideas what could be causing this ?
I will have a look at flushing the cooling system through and re-filling it tomorrow in case its full of sludge, how should this be done (flushing) ?

A link to a post in which I mentioned how to fill with coolant from an empty system (it is in there towards the bottom of the post).

Is there coolant or just water in yours? Surprised there would be sludge, I guess you'd need a radiator flush solution if you do suspect sludge.
Could be there is an airlock in the system, follow the way I filled mine up - via the radiator cap and not the expansion bottle. If that looks OK, maybe need to check the thermostat.

Oh Hi and welcome

Thanks for the welcome and the link.

It looks as though there is coolant in it. I doubt there will be any sludge in it but figured it best to flush it in case. I was wondering if a blockage could cause the coolant to boil in the expansion tank. To be fair i would expect it to overheat if it was blocked but the temp is reading ok on the gauge, assuming the gauge is correct.

Welcome PG,

Most (if not all) the cats I have known run at approx. 80^o and can rise up to 105^o on a hot day pootling around before the fan kicks in.
I don't recall anyone reporting a coolant dump in the manner you describe. So, as Stevecat said above I'd suspect an air lock in the system too.
Hope you get it sorted soon, I'm sure it'll turn out to be something simple to overcome.

Welcome again, have a good look around the forum(s) . . . And we hope you enjoy

Cheers
Tel

PS: Pop into the New Members section and say Hi, I'm sure you'll get some more warm welcomes

Hi and welcome

If it's boiling at that temperature check the radiator cap is on properly and the spring's still good, sounds like there's no pressure in the system. Had it with Cat's CBR, the radiator cap wasn't sealing properly (and the fan wasn't working but that's a separate issue) and it was boiling

Another thing to consider, I'm afraid, is the head gasket. As stated above, the Cat will happily get over 100°C when sitting in traffic without boiling the coolant.

Is the fan kicking in?
If not it could be a faulty thermostat.

iirc it kicks in over 80, so if it's sticking below that....

Hi again, things got in the way so have'nt had a chance to get out into the garage until today.
Drained the fluid and it looks like i have less than a litre in there !
Leaving it to drain for a while just in case any more wants to come out, then going to run the hose through it.

Forgot to mention there was no oil in the fluid (or antifreeze) and no water in oil so hopefully head gaskets ok.
Also it was'nt getting hot enough for fan to kick in which is surprising considering the amount of coolant in it. Mind you it does'nt get a chance to sit in town, only open roads.

OK, second wsb race finished so run hose through it, hose in rad cap. Flowing freely from the bottom rad hose but there is as much water coming out of the overflow as there is out of the engine . Could this just be due to the waterpump restricting flow ?
Have kinked both rad and overflow pipes to force it through engine but i suspect all is ok so going to leave for a few more minutes and then re-fill.

After re-filling i got my first chance to take it out today and all seems well, sitting at just over 60 degrees and no boiling up.
Just got to change that hideous screen now before i can let it be seen in public !

Quick update, all has been well for the past few weeks with the temperature nice and stable and no boiling, assumed its sorted.
Took it to Margate today and all was well until i got there. Once i hit traffic it boiled up spewing coolant and steam from the overflow, lost count of the amount of people who told me it was leaking. At least now i know the fan works !
Topped up with water once it had cooled down and when i left it was at normal temperature for a few miles but soon got upto about 100 where it stayed all the way home.
Clutch slipping now as well

Possibly a combination of the thermostat and temp sender unit. 
One could be telling porkies on actual temp so misleading you.

yeh ^ that, i dont think mine ever ran at 60, and i've also seen 105 when sat in traffic (brighton bike meet) on a sunny day.

could be that the fans not coming on soon enough

the haynes manual tells you how to test the temp sender.

I know this all seems a bit drawn out, not getting a lot of time at moment, could just do with a bike that works !
Have changed the rad cap today for a known good one so that's ruled out as it boiled up again. I will try to test the thermostat and sender when i get a chance and have my fingers crossed thats the problem.
I want to resolve the boiling issue before i get stuck into the clutch but that is now pretty much slipping all the time, on the plus side i suppose it might help it to warm up quicker !

Things like these are sent to try us 

Got a day off at last !
Tested the thermostat and it works fine so it aint that, this just leaves the temp sender to test which i will do shortly when i find it in manual. Having said that surely this just tells the fan to kick in, which it does, and the gauge to work.
Assuming the temp sender turns out fine where should i be looking next ?
If the advice is the head gasket how do i test it ? bearing in mind there is no oil in the water or water in the oil (or water in the water for that matter !)

Thinking about this and what about the water pump. It may be in intermittent fault/blockage and boiling the water which isn't passing through the pump

Is there any way to test the pump ?

Just looked it up.
Looks like i need a thermometer for the temp sender and a couple of o rings for the pump.
Best go to the pub !

Are you after this o-ring?

The listing's finished, but still have it.

Yes, that's one of them. Going to take it apart today to have a look.
This bike is gradually ending up in more bits than the one i bought it to replace !

Does'nt look like its the pump.
I can't decide whether to put it back together or continue stripping it down and selling the bits !

The 'cat takes a fair bit of abuse to boil, regardless of the problem the fan should cut in before it boils, have you bypassed the fan switch to test the system? My FZR got worryingly hot on TOL last year despite knowing everything was working ok, turned out to be corrosion on the switch contacts.

Hi, the fan does work. I was thinking the same thing. The last time i took it out (and almost every other time) it was boiling up whilst on the move, not caning it but at a decent speed and that is without having to stop for lights, junctions etc. It had proper coolant in it and not just water, oil was good, to the correct level and nice and clean, only issue was clutch slip but once it had a couple of miles under it that was only bought on by giving it a big handful of throttle, which i avoided.