Coolant level

[albuquerqueturkey]

Hi foccers. Got home from work on my gen2 today and about a minute after parking up it spat some coolant out of the overflow coming from the expansion tank, about a 1/2 pint. The bike didnt overheat on the ride.


The level on the bottle has always been at the full mark when cold since i flushed the system and refilled with coolant last July. The level now sits about half way between low and full when cold, and the radiator is still full to the top.


I know some bikes don't like the level being at the max like my old vfr which always sat on the minimum line, but I don't understand why its only decided this now about 2k miles later?


I ran her up again and got both fans working at 100 degrees, the stat seems to open at around 77 as the temp drops down to 70 before building back up. I took her out again and all seems normal. Im thinking possible dodgy stat?

[Gnasher]

With the bike cold the level should be between the lower/upper makrs not on the upper level. 

If you drained the bike last July and have hardly ridden it since?  It's not surprising, as the system hasn't had sufficient time to self bleed and air locks are common.  The reason the level isn't at the top in the expansion tank when cold, is given away in the name 'expansion' this allows for the heated water in a sealed (pressurised) to expand, if it didn't it would burst the rad or a pipe.  When hot the level will rise to approx the upper level as long as the system isn't spitting out coolant when it's hot or just after being turned off, with the level filled to half way between the marks when cold. 

Your system sounds fine to me. 

[albuquerqueturkey]

Thanks Gnasher for your reply.


I have checked again this morning and the level in the tank is a little below halfway between low and full. The rad is still full.


I will keep an eye on it.

[teecee90]

Just keep an eye on it. If it happens again, I would probably start by changing the radiator cap.

[Gnasher]

Just keep an eye on it. If it happens again, I would probably start by changing the radiator cap.

Why?  If the rad cap fails it will leak, thus there's no pressure in the system and the expansion tank would be empty 

[teecee90]

I thought the rad cap was effectively a pressure relief valve. Surely if the "valve" goes weak it can open too early and cause overflow?

[Gnasher]

I thought the rad cap was effectively a pressure relief valve. Surely if the "valve" goes weak it can open too early and cause overflow?

The cap is an on/off valve but it shouldn't leak it will allow coolant into the expansion tank, via the expansion pipe.  If the cap is leaking, in turn the expansion tank will try and replace the lost coolant and will either be empty as too much needs to be replaced or or lower, but as the cap leaks over time it will empty.  Unless you add water which in itself is telling you, you've got a problem.     

The clue is in the name expansion 

If the rad cap is leaking you will have traces of dried coolant around the rad cap, no matter how small the leak, it will be there and if the cap it leaking the system will no longer be pressurised so will run hotter.  Depending how bad the bike will boil or overheat.   

[b1k3rdude]

The cap isn't a valve it's a cap

+1 and most japanse bikes just have a cap, with the thermostat (which is what I think TC90 was thinking of) being below the cap on this bike. @TC90m I think your confusing other vehicle types, some of which have the thermostat built into the cap.

[Decoke Dave]

   Daft question time. The expansion tank simply has a push on rubber plug/cover, how is the expansion tank “engine up to temperature, thus full pressure” isolated from the cooling system in a fashion that the expansion tank can top the cooling system up without its contents simply being pressurised thus blown out everywhere! A car expansion tank has a cap which retains pressure on a car?

[Gnasher]

Most bikes don't have a rad cap, I did, just for reference purposes as teecee90 referred to the cooling system cap as one.

Most bike don't have the filling or main cap on the rad they can be anywhere, they tend to be mount in the thermostat housing.  Personally I've never seen a rad/filling cap with a thermostat built in, temp or pressure gauges, yes.   

[Gnasher]

   Daft question time. The expansion tank simply has a push on rubber plug/cover, how is the “engine up to temperature, thus full pressure” isolated from the cooling system in a fashion that the expansion tank can top the cooling system up without its contents simply being pressurised thus blown out everywhere! A car expansion tank has a cap which retains pressure on a car?

The expansion tank hose is usually fitted in the filling neck somewhere if the pressure builds beyond the either a built in pressure valve or the filling cap (spring) it will slightly, open the valve/cap and allow the pressure (coolant) out/in into the expansion tank.     

[teecee90]

The cap is an on/off valve but it shouldn't leak it will allow coolant into the expansion tank, via the expansion pipe.  If the cap is leaking, in turn the expansion tank will try and replace the lost coolant and will either be empty as too much needs to be replaced or or lower, but as the cap leaks over time it will empty.  Unless you add water which in itself is telling you, you've got a problem.     

The clue is in the name expansion 

If the rad cap is leaking you will have traces of dried coolant around the rad cap, no matter how small the leak, it will be there and if the cap it leaking the system will no longer be pressurised so will run hotter.  Depending how bad the bike will boil or overheat.   

Presumably the valve within the cap could fail but the upper seal remain intact? That could presumably result in no leakage from the radiator cap but 'blow off' of excess coolant through the valve at a lower pressure than specification. The excess going into the expansion tank and ultimately out through the overflow if enough of it?


On the gen1 the cap is not just a cap, it is also a valve (with a specified pressure rating). Not sure about the Gen 2 though....

[Gnasher]

Presumably the valve within the cap could fail but the upper seal remain intact? That could presumably result in no leakage from the radiator cap but 'blow off' of excess coolant through the valve at a lower pressure than specification. The excess going into the expansion tank and ultimately out through the overflow if enough of it?


On the gen1 the cap is not just a cap, it is also a valve (with a specified pressure rating). Not sure about the Gen 2 though....

Anything is possible, that said I've never seen fill cap fail in that way.   If the seal on the filler cap fails, it will leak coolant, the system will over heat as the system can't pressurise, it wont go up the expansion pipe, as it will take the path of least resistance i.e. out of the filler port.  If coolant is blown out of the expansion tank, the system was/is either over filled and/or the system is blocked somewhere, water pump has failed and the engine is now boiling it's self.

[teecee90]

 If the seal on the filler cap fails, it will leak coolant.....

For a valve type cap I guess it depends which seal fails. If the upper seal fails then coolant will leak out of the cap. If the lower seal fails then it will leak into the expansion tank.

[Gnasher]

For a valve type cap I guess it depends which seal fails. If the upper seal fails then coolant will leak out of the cap. If the lower seal fails then it will leak into the expansion tank.

Nope, if the lower seal fails the system can't pressurise and the engine will overheat, it very short (a few mins) order, it won't leak it will boil! If you ignore the temp gauge and the steam/coolant peeing out of the expansion tank all of which will be blatantly obvious.  You'll blow the motor

None of that happend to this chap.   

If the upper seal fails again no pressure same effect as already mentioned and obvious coolant staining around the neck again this chap didn't have that.  Mate on this occasion based on symptoms this chap has provided, it's got nothing to do with the cap.      
 

[teecee90]

Ok