Coolant boiling

First topic message reminder :

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) ?

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.

Finally got a thermometer.
The fan switch and thermostat both check out ok. The water pump looks and feels good.
There is a bit of limescale buildup in both the thermostat housing and the pump housing but not enough to block anything, running a hose through the rad works so pretty sure its not blocked but will run some rad flush through.
I am going to get another rad cap just in case the good one i have put on is also faulty.
Any other ideas ?
Any tips on how to check the head gasket ?

I was going to suggest a compression test, but as a self confessed worlds' worst mechanic I thought it best to Google it first.

This is for a car, but the principle should be similar. Link to PistonHeads article. The last post seems to have some good ideas.

Thanks stevecat
I do have a compression tester but need an adaptor to fit the cat, i am a little concerned about diagnosing with this as there could be any number of other things like valves, piston rings etc wrong. Admittedly it would'nt hurt to know about these anyway but might detract from diagnosing the original fault.
I am thinking of bunging some block seal in it to see if that makes any difference.

Whilst i am waiting for the rad flush to turn up i think i will take the rad off and try running water through it in reverse, ie upend it and run it through from the bottom. If there's limescale in the pump housing and thermostat housing it could be that its blocked but the water is still able to get through a couple of passageways, by running it through in reverse it might dislodge some if its in there.

A compression tester will only check the integrity of the cylinders. You need a leak down tester to see what the problem could be if there is a leak from intake/exhaust valves, piston rings or head gasket. To be honest a compression tester is not worth it as you would still be guessing what the problem is and either a stripdown and measure everything or a leak down tester is the way to go. If your not getting coolant in your oil, losing oil and other than the over heating the bike is running spot on then the chances of a gasket/ring/valve issue are very slim. If i were you i would take apart and check and clean all componants of the cooling system first before spending money out on equipment that might not be needed. Coolant pump, temp sender unit, all pipes for blockages/holes/tares and also the radiator.

Once checked, reasemble, fill up via the rad and NOT the expansion bottle. Run up to temp with the rad cap off to get any air out the system and if need be top up while its running to top of rad 9you will get coolant coming out while it pushes air out). Once thats done leave to cool down for a couple of hours then top up system via expansion bottle.

Is there a way to get the metal pipe to come out of where it is joined to the water pump and where it goes into a housing at the back of the cylinders ? Mine is stuck fast and i could only get it to move from the pump housing by a few millimeters and not at all from the other end. I did'nt want to force it as it feels like it will deform pretty easily.

There is an o ring on each end, undo the two allen head screws holding it on the get a small rubber mallet and hit each end, once the o rings are free it will just come away

Radiators good and clear, no way its blocked. It does have a few mashed fins but not enough to cause a problem so i think i can rule that out.
Running out of things to test/check.
I did fire it up and it looked a bit smokey, i suppose this could be condensation but got a bit fed up with it for the time being.
Was offered a zzr1100 out of the blue at the place i was working today, got all excited, checked my bank balance and everything and then the guy led me to a bush in his garden, i think it was in there ! He wants £600, i did'nt manage to not offend him !

Put the rad back on it today and filled it up with tap water and some rad flush. Fired it up and left it running for about 10 mins then decided to run it round the block to avoid upsetting the neighbours.
Eventually i have put about 25 miles on it, mostly at high revs to get it nice and hot but it just hovered around 60-65 degrees only rising to about 80 when i went through the town as slowly as possible.
Left it sat running when i got home and it crept up to around 100 when the fan cut in and it then dropped again.
When i turned it off i could hear bubbling in the expansion tank under the seat but there was nothing coming from the overflow.
Does the tank on these sound like it bubbling once its got hot or am i still not in the clear, i am still concerned because i thought all was well before but it just boiled up after a reasonable distance.
I will have to put some proper coolant in it and give it a reasonable run next week if i get the chance.

If you only put water in then it wouldn't surprise me if it would bubble    
At least it didn't boil over so yeah try it with coolant and got my fingers crossed for you

Apologies for the late reply to this thread but I have the exact same problem described in the first post, Temperature seems fine 60-80 but the water bubbling and spewing from the overflow is a tad worrying :(

No water in the oil or oil in the water and no other issues except my fan doesn't come on :( The fan does work as I tested it by bridging connections but it's never come on automatically.

Anyhow, Did this issue ever get fixed

I believe the issue was an airlock in the cooling system. Have you replaced your coolant or any pukes recently? Try what I posted above first.

Better late than never But I finally fixed the problem.

It was simply the radiator fan sensor switch. I bought a new one from aliexpress for around about £10 and it's been perfectly fine ever since. They are also available on ebay and other places for around the same price.

T1Cybernetic wrote:Apologies for the late reply to this thread but I have the exact same problem described in the first post, Temperature seems fine 60-80 but the water bubbling and spewing from the overflow is a tad worrying :(

No water in the oil or oil in the water and no other issues except my fan doesn't come on :( The fan does work as I tested it by bridging connections but it's never come on automatically.

Anyhow, Did this issue ever get fixed

T1Cybernetic wrote:Yes the coolant was replaced recently But I've been riding a few times since then, I think I've done around 600 miles and never had a problem.

The oil is clean, The water is clean but I haven't had chance to test anything except the fan yet! I was just doing some research before I start to take things apart

I'm hoping it's a sticky thermostat or something simple like that :( I would hate to think it was anything major !!!