Coolant not returning to radiators.

Hi all,as the title suggests I am having coolant issues on my 5th gen.
Symtoms; after an hours ride to work the coolant has expanded into the expansion tank,but when it cools down It doesnt return into the radiators.
It goes from lower fill level to upper level.So maybe 100ml?
I put on a new (non honda) radiator cap.Same result.
So far I have put pressure into the overflow tube (about 16psi)and found a few weepy hoses due to loose hose clamps.Still same result next ride.
I transfer coolant back to the radiators and there seems to be no loss of coolant.
Next step I found a faulty thermostat(stuck open) and of course more loose hose clamps on the thermostat housing.
After installing new honda thermostat, result the same next ride.
Bike is not over heating.
Spark plugs look like a nice tan colour.
Bike is actually running really well.
It sounds like I still have an air leak somewhere?However it seems to be very hard to see.
No coolant in the oil.However I have only just changed it.
Bike has 100k on it.
Has anyone else had the same symtoms?
I am running out of ideas.
Cheers.

 

Are you sure the cap is right?
Only way air can be sucked in is through cap or tank link hose.

 

Double check for leaks. If any air can be pulled into the system as it cools down, it will.

 

I have tried 2 new caps as well as the old honda one.Same result with all of them.
I am pressure testing it again today and I also want to make sure that the water pump drain hole is clear.
I thought that perhaps if the waterpump was leaking then maybe that was where the air leak is coming from.
Although I would be losing coolant if that was the case?
I will pull out the hose that goes from the expansion tank to the filler neck and pressure test that under water as well.
I am spending another cold rainy day tinkering again in the shed.
But at least I am learning new things,and its free!

 

With the motor cold remove the fan switch in the top corner of the left radiator. Coolant should come out, if not it likely has an air pocket needing to be burped out.

 

Today I pulled off the radiators and flushed them out.Degreased and cleaned the fins.
Checked the water pump drain hole.All clear and dry.
Its all back together now and I took it for a short ride.I then stopped and let it heat up till the fan came on and now I am having lunch and waiting till it cools down to see if anything has changed.
While I was there I also synced the starter valves.
Boy it is really running sweet now!
And I dont think I have any air in the system because I let it warm up with the cap off and I have a large funnel that I use to alllow the air to come up while I burp it.

 

about the cap of the filler cap of the radiator already wrote?

 

Latest update to coolant issue.
I have had a mechanic test at the radiator for signs of hydrocarbons and the test came up with a very very slight amount showing.
So I guess I may have a slightly leaking head gasket.
He suggested that I just put in a bottle of something that will patch it up for a while.
Although he wasn't 100% sure that was the source of my troubles.
I am thinking about it.
But I think that perhaps in the long run it will probably be better to get the head gaskets changed.
I know the bike, and it has served me well for the last 9 years and 70,000klms,so perhaps I should just order some new gaskets from England and get on with pulling the motor out!
It would give me a nice winter project to do as well.
Has anyone else had to do their head gaskets?

 

Before you condemn the head gaskets do a compression test and a cooling system leak down test....

 

I am still looking into the compression test and leak down test,however just to confirm that I am on the right track.
When cold the expansion tank is at the lower level mark.The radiator filler neck is filled to the brim then there can be no air getting into the system.Making sure that I have bled all the air out using the large funnel while running the bike and blipping the throttle.
When I have ridden for about an hour the coolant has risen to half way between the upper and lower marks.(normal I guess)
When I let it cool down, the coolant expansion tank has gone down slightly,but there is now an air gap under the radiator cap.
My conclusion is that there is still air getting into the system from somewhere?
Its driving me nuts.
I think I may have to take it into a real mechanic to get a diagnosis.

 

The same error occurred to me.
Did you find the solution?

 

Hi.In the end all I did was, when it was cool I undid the radiator cap and then squeezed the lower large radiator hose till the coolant level rose to the top of the filler neck.
And when you put the radiator cap back on there is no air in the system.
It fixed the problem for me.
Its been all good from then.

 

Thanks for the reply.
I try it.