Another (minor) heating issue

Hi all,

Time for an update, albeit not a very good one I believe. As a reminder for new readers, initial symptoms were that the bike suddenly started heating up more than it used, noticeably, which lead so some piddling on the pavements on warm sunny town rides. I tested the thermostat, even removed it at one point, all OK. Changed the waterpump, no luck. Cleansed the radiator, flushed the cooling system, to no avail (no muck found anywhere, nothing seems clogged)
Since then, and very recently i did the following :
- driven a whole 15000 miles, no other symptoms (but always have been weary about hot summer days, avoiding towns as best as possible. However, fan works fine, and stops the needle from going into the red and stabilises effectively the heat roughly half way up.
Recent maintenance, 500 miles ago, as follows :
- Valve clearance : was slightly off, now perfect
- Oil changed : no water in it
- Coolant changed (many times) : no signs of oil or mess in it
- Filters all changed
- new sparkies

Unfortunately, noticed the bike was piddling again the other day, after only 15miles, in the cold, no town driving. Not at all the usual behaviour. I checked yesterday, as the engine warms up, pressure builds in the expansion tank, the level is way beyond max now (wasn't before - it was spot on), and it piddles. With the cap off one can see big air bubbles generating in the expansion tank and popping. It's not the usual piddling, after topping off with too much coolant, it's not continuous. So now the bike can't be used in my opinion - air bubbles will form in the cooling system and I risk overheating it now.

Spoke to a very helpgul forum member about this, and we both seem to have a good idea of what this may be. But I'll ask an open question anyhow, maybe we are forgetting something : what could cause air bubbles to appear in the coolant expansion tank?

I'm in the process of getting a new radiator cap, cheap second hand (but should be fonctional), to continue ruling things out. But now the time has come to find a real fix I do believe!

My cb was blowing coolant out  of a hose pipe and it was bubbling in expansion bottle too, i feared the worst, i taught head gasket was gone. The rad was stil full of coolant, i got a second hand thermostat and radiator cap, i only fit the cap so far and its been fine

@wornsprokets wrote:My cb was blowing coolant out  of a hose pipe and it was bubbling in expansion bottle too, i feared the worst, i taught head gasket was gone. The rad was stil full of coolant, i got a second hand thermostat and radiator cap, i only fit the cap so far and its been fine

Well, there is hope then! Thanks for sharing.

I should mention the liquid being pushed out is cold (no surprise really, but anyway, it's no boiling : fan works fine and doesn't get a chance to kick in).

I took the tank off this afternoon checked, indeed level of coolant was lowish, and air bubbles had started forming. The piddling seems to occur when the engine is at temperature, but clearly not overheating. Will test again with the cooling system to a level, but I don't think air bubbles are forming when the engine is cold. Also, when I rev the engine, I see the coolant level (rad cap off) go down and move a fair bit, which, to me, suggests coolant flow is unhindered and that the pump is indeed working.

I've ordered a second hand filler cap to test, and will also try to find a garage that can do a sniffer test for me, I need to gather some more information, this one is tricky!

If it were to be a head gasket, would it simply be a case of changing it? (Assuming no damage, ie warped cylinder heads etc has be done)

Take plugs out see what there like, my cb was not over heating  it runs cool never seen it in red , when i took off radiator cap ,  there was no bubbles in coolant i put little coolant in rad but it was very little, if head gasket is gone and its only minor and heads not warped theres stuff called seal steel its expensive but ment to be good  i never heard of it been used in a bike , oh and expansion bottle was empty after leak,

@wornsprokets wrote:Take plugs out see what there like, my cb was not over heating  it runs cool never seen it in red , when i took off radiator cap ,  there was no bubbles in coolant i put little coolant in rad but it was very little, if head gasket is gone and its only minor and heads not warped theres stuff called seal steel its expensive but ment to be good  i never heard of it been used in a bike , oh and expansion bottle was empty after leak,

Thanks - spark plugs both look fine, not too white, not too oily either.

If it were a gasket issue, wouldn't be better just to change the gasket? No idea what seal steel is - do it have to be used in conjunction with a new gasket or is it a fix?

Doing my best to get a new rad cap asap, that will rule out (or hopefully solve) a problem.
Also need to do the sniff test asap.
Finally, forgot to mention, but bought a compression kit test online. Could also give additional info as to the problem.

So far, the way I see it, only a head gasket or a faulty valve (that would have to be the rad cap I believe) could cause bubbles in the expansion tank, and spueing of coolant on the ground via the overfill. Please correct me if I'm wrong though!

If the rad cap was faulty and not holding pressure then as soon as the coolant started heating up it could allow coolant to be pusehd past its seals and down the tube, along with any air in said tube, to the expansion tank.

I imagine  the compression test wil tell you if headgasket is gone, i think it be costly to do headgasket, cheaper to source a new engine. Yes my expansion bottle was bubbling up and then its contents went on the floor via a pipe from bottle, it wasnt a regular thing it happened three times i say. The steel seal solution is put into radiator and its ment to fix a small head gasket problem but not 100 percent to work(have look on you tube) its a good sign your plugs are fine. Try cmpression test and new radiator cap before u do anything else

Sounds like the thermostat to me. Annoyingly expensive (~40 quid) but an easy fix.

The thermometer, which governs the fan, is I think in the Rad. So if the radiator is never having hot coolant (funny contradiction in terms!) washed through it, it will never know the engine is overheating.

@Beresford wrote:

@wornsprokets wrote:The steel seal solution is put into radiator and its ment to fix a small head gasket problem but not 100 percent to work(have look on you tube)

WS - don't trust those sealant additives. They may fix the gasket but they fuck up the radiator core tubes.

Thanks. That was my feeling too ; if something is wrong I'd rather fix it properly, I don't really believe in those magic fixes that break something else down the line !

Thermostat is fine. Gets warm evenly, and bike was even tested without it.

I have a new radiator cap coming in Friday,  and hopefully also the compression tester kit. As well as a decent auxiliary fuel tank which should help work on the bike !
First test is simply to chabge the cap and hope that does something...

Thanks for the ideas.

Steal seal was last resort, if you were going buy a replacement engine next. Not good if it block up radiator  core didnt know that. As i said before radiator cap did trick with mine

Thanks, yeah. But a gasket a quite cheap really. Assuming cylinder heads are not warped it should be a "simple" job of changing the gasket , right? Takes a fair few hours but if it can be done at home then why not.

Anyway, first step,  cap!

Well well well... At least one problem has been solved : radiator cap was faulty !

No sure about the initial problem on the thread (heating more than it used), haven't ridden and the hots days are not quite there, but the bike has stopped piddling anyway. Hurray!!!

What a relief. I was dreading taking the engine apart just as spring is showing up!

Thanks again for all your input and help.

Glad to hear it was something fairly simple!

thanks Beresford that's well worth knowing

@Beresford wrote:FWIW I believe that the cap is the same as is used on some Japanese cars (Subaru ?) and can usually be bought from your happy local motor factor for not very much.

Hello Chaps,

Got the same problem with mine, anyone know a cheap TP pressure cap that fits or if the Subaru 1.1 bar does, as mentioned above does?

Many thanks