Cooling it

[StuartWags]

Just a few comments that may or may not help.

The tube in the expansion bottle should always be covered with coolant, hot and cold. If not there is a danger of pulling air in when the system cools down. The rad cap actually has a high pressure and low pressure flow. Air in the cooling pack is not desirable.

Cooling systems always trap a bit of gas on fill but this should be pushed out to the expansion bottle as the coolant expands. The rad cap is at the highest point to help this. This is normal and desired. And if the tube is covered with coolant in the expansion bottle it will suck coolant back in when it cools down

If there is a lot of air trapped in the system it can cause issues with cooling efficiency as the pump don’t like pumping air or aerated coolant. The aeration occurs at high pump flow rates when the coolant starts to mix with the trapped air. This can lead to overheating.

What is boiling?
“Boiling is the rapid vaporization of a liquid, which typically occurs when a liquid is heated to a temperature such that its vapor pressure is above that of the surroundings, such as air pressure”

What that means is that boiling does not make extra air (or mass), it is a change from a liquid to a vapour and the vapour wants to take up a lot of space at the same temperature and pressure. Hence, coolant ejections in belches and burps as the vapour forms.

So if there is a slight boil, coolant is ejected to the expansion bottle. But on cool down, this should be sucked back in.

If you have a continuous stream of steam coming out of the vent and the rad cap is working, and you are well below fan operating temperature, and you have previously brim filled and purged the system, this is worrying. Under these conditions, I would say head-gasket leak to coolant. If I doubt, it might be worth getting leak detection kit and checking for CO2

Hopefully, I have misread or misunderstood the description of the symptoms. I have had issues purging air out before.

[Martinz]

Just a few comments that may or may not help.

The tube in the expansion bottle should always be covered with coolant, hot and cold. If not there is a danger of pulling air in when the system cools down. The rad cap actually has a high pressure and low pressure flow. Air in the cooling pack is not desirable.

Cooling systems always trap a bit of gas on fill but this should be pushed out to the expansion bottle as the coolant expands. The rad cap is at the highest point to help this. This is normal and desired. And if the tube is covered with coolant in the expansion bottle it will suck coolant back in when it cools down

If there is a lot of air trapped in the system it can cause issues with cooling efficiency as the pump don’t like pumping air or aerated coolant. The aeration occurs at high pump flow rates when the coolant starts to mix with the trapped air. This can lead to overheating.

What is boiling?
“Boiling is the rapid vaporization of a liquid, which typically occurs when a liquid is heated to a temperature such that its vapor pressure is above that of the surroundings, such as air pressure”

What that means is that boiling does not make extra air (or mass), it is a change from a liquid to a vapour and the vapour wants to take up a lot of space at the same temperature and pressure. Hence, coolant ejections in belches and burps as the vapour forms.

So if there is a slight boil, coolant is ejected to the expansion bottle. But on cool down, this should be sucked back in.

If you have a continuous stream of steam coming out of the vent and the rad cap is working, and you are well below fan operating temperature, and you have previously brim filled and purged the system, this is worrying. Under these conditions, I would say head-gasket leak to coolant. If I doubt, it might be worth getting leak detection kit and checking for CO2

Hopefully, I have misread or misunderstood the description of the symptoms. I have had issues purging air out before.

Cheers for this mate. No the bottle has always been dry / empty before start up. Going to fit everything today.

[Martinz]

Well, that didnt fix it .....

so after the bike is boiling over and i pulled over, it sounds like all the bubbling / boiling noises are coming from the left coolant pipe ??

thermostat ?

[tony.mon]

Suggest you take the fairing off, remove rad cap with engine cold, then have a look at the levels. You should see that the level drops an inch or so as you blip the throttle.
Start it with a cold engine and allow it to run up to fan working temp with the rad cap off.
Don't get too close, as it might splash, and wear eye protection.

If you have a head gasket issue then it will bubble and splash out when cold as well as hot- it shouldn't do this.

Tips: when topping up, squeeze the LH top pipe (the big one) which should bleed any residual air out of the system.
To ensure the fullest level, on a warm, not hot, engine, open rad cap, hold throttle at 2000 or so, add water/coolant mix, then refit cap, then let go of the throttle.

[VTRDark]

Try not to burn your hand while squeezing the hose I find the lower ones need need a squeeze too to help get any trapped air out. The Honda manual recommends blipping the throttle but a squeeze does no harm and helps.