125-200cc wre 125 cooling problem

bike starts up easily, first kick, coolant level is topped up, ride bike for ten mins or so, then as soon as I turn off the engine the radiators go ''HISS BANG, BANG! HISS! BANG!'' for maybe 20 seconds. Then coolant comes out the overflow pipe, in short bursts for maybe ten seconds, a considerable amount too. I let bike cool down, retopped up the coolant which was now below the top of the fins, rode again, same thing happened. I can't see any leaks on the cylinder, the spark plug and head feel dry, the base gasket appears fine. No visible leaks from either radiator or the hoses and all of them are warm/ hot when bike has been ridden. I rode for 70 miles a few days back, and the same hiss bang thing happened when I filled up with fuel, and that time it was almost empty of coolant by the time I got it home to fill the rads back up. What is going on??

Sounds like your boiling it, cold engine start bike open rad cap look at coolant when you rev should whirpool if it does you can rule out water pump.

What % antifreeze you using as water boils at 100• anti freeze mix boils at 180 ish,
Pure antifreeze boils at 375odd but engine will run hotter as its thicker than just water so you can still overheat a motor using evens fluid and similar.

Hows the rubber seal on rad cap ? Also make sure theres no dents on the rad side of the cap.

Oh if when you revv the bike with cap off and the water comes straight out your rad you have a head gasket faliure, are plumes of white smoke bellowing out behind you?

have tried the genuine husky cap, they're chinese radiators but have worked fine for 2 years prior to this, the cap that came with them does the same thing, using a 50/50 ready mix of anti freeze from halfords, says it protects up to 108 degrees and -34 freezing. Drained all of it out a week ago as it kept loosing a little bit of coolant then refilled, now it does this. I started it cold just now and the coolant does seem to be moving a little when I rev it, but not a whirlpool. however after 3 minuters running it definitley moves with revs

no white fumes except normal two stroke ones, no coolant stayed in the radiator with revs, all it did was move around at a similar level, it didnt jump out

Humm its a mystery do you have thermostat on the wre? Could be sticking.
If two caps do the same thing you can almost rule that out, 50% mix ahould be fine i use 33%.
Bit of a conundrum youve checked the blindingly obvious normally that solves it for me...
And now over to an experianced person.

there is a thermo stat wire I believe but it hasn't bveen connected to the head for 2 years, I think the garage guy said it was easier just to leave it hanging down, probably so the waterpump comes on all the time instead of relying on a thermo which might break and then overheat the engine. Only thing I can say is it was only loosing a little bit of coolant every ride, then I drained it out, tilted bike side to side then refilled, now it loses a lot, maybe there's air stuck in it or something

allright, just watched some how to vids on coolant change and seems I may have made a big error, when I filled coolant back up after draining I just put cap on and rode, didn't idle it with cap off to let air esacape. I think maybe I've now got a mahoosive air lock so tommorow I will fill to the top of rads, idle it for ten / 15 mins with throttle blips until I see air bubbles coming out. If that doesn't work I am at a loss

perhaps try filling, putting cap on, then tillting bike over pretty far to each side to shake some air loose? does your bike actually have a thermostat in the system?

I filled it, tilted it side to side, quite far over too, and it kept making bubble sounds, did that for a few mins, then started it still cap off, ran it on low revs for about 20 mins, squeezed the hose that goes from rh rad to waterpump, and after a bit bubbles started coming up in the radiator top, it seems to be cooling the engine as the exhaust didn't feel THAT hot on my hand but the rads them selves were hot afterwards. I stopped engine then put cap back on. The air bubbles didn't come up by themselves though, it was only when I squeezed the hose. I switched it off after 20 mins as I thought the coolant would be getting too hot and didn't want to cook my engine. The bike is supposed to have a thermostat yes but it is now just a wire that hangs down by the head, the old head blew a hole so it now has a newer but used one, doesn't appear to be any place for a stat to connect to it, so the garage I got to put it on said they would just leave it so the pump came on straight away, hasn't had any problems before

So take it for a blast and see if it boils over again, we ask about thermostat as if the units left in situ it will cause a airlock. If the garage claim to have removed it i would double check but thats me. The wire going down i assume is for your dash thats a temp guage.
A thermostat traps water in the cylinder untill it hits about75• then opens heating up rest of coolant.
Most enduros dont need them as the whole system holds less than 2litres.

rode it , could hear it banging in the rads again so came back, turned it off, same problem but this time no coolant came out the overflow. The pic shows the wire I mentioned, it's got a thin end to it like a female to male connector but it's taped off atm. If that is a temp gauge wire like you said, where is the thermostat located? I had this exact problem on my corsa and that was sorted once we changed the stat

Go on halls cycles and search for the manual for your bike, look at parts diagrams and see if it has one and where it is.
The most powerful tool we have is at your finger tips a little search and you will learn what you need.

Thermostats are normally in the hose somwhere or on a fair few bikes is in the head and a hose plugs right into the case above it.

I took off the head, replaced to orange o ring in case it was that, fiddly little thing to hold in place, took off the waterpump and a plastic thing fell in my hand in two pieces. I believe this is the issue. Impeller not able to spin to pump water, surely this would be the overheating problem

wow, split right in half. very fortuntate you didnt keep running it!

yes, the last few days I did hear something rattling in that area on cold startups, I thought it might be the bottom end at first but this must hve been the cause. Properly hard part to find though! I'm going to ring the dealership and hope they have one in stock!

if it costs too too much just get a spare sidecase at a breaker..oddly, sometimes thats a better deal and you get more stuff..let us know how you make out

Wtf why is that not metal? Never crossed my mind that it would be impeller!
Good find gazmcfaza.
Good luck finding replacment.

Good news everyone! Yes it was the impeller, called husky dealership, had one on the shelf, came yesterday fitted today with new gasket, filled with fluid shook side to side, ran engine etc, took for a ride guess what? NO POPPING! NO BANGING! and after cool down, fluid level as it was, just above the fins but below overflow so if it goes again I'll know where to look first. I have no idea how that didn't overheat as I was doing 70 mph max with it still. One weird thing, the shaft that comes out, well it does turn with the kickstart, but to put the impeller on you have to screw it on, but there's no way of tightening it, and when the shaft turns, it turns the impeller backwards the way that it would go to UNDO it. It only goes on that way too. I don't think that's very good nor is it to make it plastic and breakable, a metal one would not have shattered. I don't get how it doesn't come undone with the force of spinning around, unless it touches the cover and that just about holds it in place