So, I started out by searching the forum and the internet and tried a few things but have not resolved the issue yet.
2006 GSX-R600, 22K miles
Starting with the Radiator full, cooling system bled, and coolant in reservoir at "MINIMUM" level.
Start the bike. Run it until it heats up. The coolant in the reservoir starts to rise slowly at about 180 deg F. When it reaches 220 deg F the fan turns on (which is also normal) and then the temperature will slowly drop back down below 200 deg F. Shut the bike down. Wait for the bike to cool down to room temperature.
At this point the reservoir is now at about the full line indicating that the coolant has not been sucked back into the radiator, like I had thought it should. If I ride hard or ride for a long time, eventually the reservoir will overflow and push coolant out the overflow line onto the ground.
Even after the bike is completely cool, when I opened the radiator cap I hear a pfft sound and the system spits some air and coolant droplets out indicating that the radiator was still pressurized.
Coolant not being returned from the reservoir is confirmed by seeing the coolant a couple of inches low inside the radiator. So I refill the radiator, go through the service manual procedure (including bleed screw on pump housing) to get the air out, and try again with the same results.
It appears air is being added to the cooling system somewhere. Enough air gets added in that as the system cools the pressure never drops back to normal atmospheric pressure (I let it sit for a few days after one run and the system still held pressure). If it was just an air bubble I would not expect the system to remain pressurized after cool down, especially with the coolant not being returned. But whatever mechanism is letting air in, does not allow air or liquid to escape over time.
It does not appear to be leaking or otherwise losing coolant. When I purge the air from the cooling system and then siphon coolant back out of the reservoir and add it back to the radiator, the levels end up about where they should be. Also, there is no sign of coolant in the oil (or vice versa).
The radiator cap seems fine, it holds pressure, but allows outflow, and the return spring and seal look and feel fine. The accumulation of pressure inside the cooling system seems to be preventing the return of fluid from the reservoir.
The air that comes out of the radiator does not smell like gas or exhaust, so I have been avoiding the headache of pulling the head to replace the head gasket.
Any other ideas? Is there any way to rule out the head gasket without pulling it?
2006 GSX-R600, 22K miles
Starting with the Radiator full, cooling system bled, and coolant in reservoir at "MINIMUM" level.
Start the bike. Run it until it heats up. The coolant in the reservoir starts to rise slowly at about 180 deg F. When it reaches 220 deg F the fan turns on (which is also normal) and then the temperature will slowly drop back down below 200 deg F. Shut the bike down. Wait for the bike to cool down to room temperature.
At this point the reservoir is now at about the full line indicating that the coolant has not been sucked back into the radiator, like I had thought it should. If I ride hard or ride for a long time, eventually the reservoir will overflow and push coolant out the overflow line onto the ground.
Even after the bike is completely cool, when I opened the radiator cap I hear a pfft sound and the system spits some air and coolant droplets out indicating that the radiator was still pressurized.
Coolant not being returned from the reservoir is confirmed by seeing the coolant a couple of inches low inside the radiator. So I refill the radiator, go through the service manual procedure (including bleed screw on pump housing) to get the air out, and try again with the same results.
It appears air is being added to the cooling system somewhere. Enough air gets added in that as the system cools the pressure never drops back to normal atmospheric pressure (I let it sit for a few days after one run and the system still held pressure). If it was just an air bubble I would not expect the system to remain pressurized after cool down, especially with the coolant not being returned. But whatever mechanism is letting air in, does not allow air or liquid to escape over time.
It does not appear to be leaking or otherwise losing coolant. When I purge the air from the cooling system and then siphon coolant back out of the reservoir and add it back to the radiator, the levels end up about where they should be. Also, there is no sign of coolant in the oil (or vice versa).
The radiator cap seems fine, it holds pressure, but allows outflow, and the return spring and seal look and feel fine. The accumulation of pressure inside the cooling system seems to be preventing the return of fluid from the reservoir.
The air that comes out of the radiator does not smell like gas or exhaust, so I have been avoiding the headache of pulling the head to replace the head gasket.
Any other ideas? Is there any way to rule out the head gasket without pulling it?