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Here's a puzzler for you, folks.

My fans have been iffy - the result of a lot of corrosion on the connector behind the rad, my diagnosis. Yesterday I spent a couple of hours fiddling, cleaned and WD'd the connection, and flushed half a tonne of calcium carbonate out of my rad and hoses.

Fans work fine now, and the coolant (despite hunting a little bit in the first five minutes) seems to be at optimum operating temperature, needle holding solid at the first bar on the gauge.

This evening, after my 12 mile journey back from work, I stopped and switched the bike off. Fans not cutting in, temperature gauge reading first bar and steady. Yet I can hear a boiling liquid in the bike somewhere. Touching the top rad hose on the right of the bike tentatively, it proves cool enough for me to hold my hand on it constantly, and pleasantly warm.

So the coolant isn't boiling. Or not all of it, somehow.

How prone to failure are the water pumps on the L models?

could be the expansion bottle bubbling, heard of a few doing that before. I know Gemini's bike did it when he had his. My ZX7 used to do it too actually. Heard it could be the cooling sytem being pressurised slightly by a blown head gasket and being released out the expansion bottle. Is there plenty of coolant in the system? I know youve refilled it but may have been some air trapped.

The coolant level isn't very low, I checked it by dipping my finger into the expanstion tank this evening.

It did sound like it was the bottle the boiling noise was coming from.

Why would it boil in the bottle and not in the rest of the system?


Also, don't say such things as 'blown head gasket', I beg of you. I think I'd die a little inside. There's no smoke, steam or coolant loss, and the oil is a healthy colour, too, rather than mayo'd.

I meant check it in the radiator level. The people who have had it i dont think have had any temperature issues so your probably ok, its when the engine starts to get cooked that its a problem. Maybe do a compression test just to check things are ok?

Vard66 wrote: Also, don't say such things as 'blown head gasket', I beg of you. I think I'd die a little inside. There's no smoke, steam or coolant loss, and the oil is a healthy colour, too, rather than mayo'd.

Myn had no other symptoms of HGF either, other than boiling coolant, and spitting a little out of the overflow.

To make you feel better though - Myn STILL 'boils' from time to time - Normally if I thrash it without letting it warm up properly.

Also sounds like you might just have some trapped air in the coolant system.

Yeah I agree, it definitely sounds like trapped air in the system. Also check water level in the rad. Only other thing is that the water pump could be on its way out.

weak rad cap, the noise is air/coolant finding its way to/from the overflow tank

Good thinking - the expansion tank cap and radiator cap occurred to me to replace earlier today, during my long ass shift.

I'll ring Cradley about them in the morning - it also occurs, surely I ought not to be able to open the expansion tank cap without massive pressure release? As it stands, I can remove the cap just after switching the bike off, without any pressure releasing. This suggests the system isn't presurising properly - which does point to the valve in the cap being shagged perhaps.
I'll also ask about a new water pump for her when I ring Cradley tomorrow, though if the CTS pricing is anything to go by I think I might have to gasp and gurgle a bit.

Expansion tank was nearly empty tonight though, which does suggest it's sucked a bit more through.

Vard66 wrote:it also occurs, surely I ought not to be able to open the expansion tank cap without massive pressure release?

Any pressure will get released through the overflow pipe

Never thought of the Rad cap.

Good point. So how does the system pressurise itself?

Or doesn't it require pressure to operate?

On another note, what's the best method you folks have found for bleeding the system?

What i meant was gas from the combustion chamber filling the cooling system (when the head gasket goes) and making its way out past the rad cap and out through the coolant bottle, causing bubbling. Just an idea thats all.

Bleeding it of air? I usually fill it up, sqeeze all the pipes to get any air out and then start the engine with the rad cap off and giv it a couple of revs. I always get a few bubbles out, then top it up and put cap on. But dont do it for too long, the engine obviously gets warm then and the coolant starts to expands and overflow.

Other method ive seen once before is a rad cap with a vacuum pump attachment on it. Saw it on american hot rod.

Yeah, someone suggested to me exhaust gas getting into the coolant - but surely there would be a drop in performance, and how would that continue to bubble after the engine was switched off.

I'd also expect a lot of steam on startup and a coolant loss, but I'm seeing neither.

your probably ok then, like i say it was an idea. Got your rad cap yet? Still doing it?

Bit of a thread , but i dont care

I have the same issue, but get the bubbling form the expansion bottle.
Everything that has been said here i have heard from other people and mechanics etc etc.

Avg price for the HG to be done?
i have a new HG here, but ive heard skimming and valves need to be done too.

Also, Vard, how did you flush your cooling system? My fan doesn't kik in sometimes. i know the fan is fine etc etc