Suzuki Club UK

Agreed, they're deffo linked problems/symptoms.

This evening I put some card infront of the rad to stop the viscous fan drawing as much air through the rad. With revs held at 2.5k rpm and a 2l bottle of coke with the base cut off,a bit of ptfe tape and placed in the rad, I was able to see the coolant expand into the bottle. With a bit of time the temp rose to 1/2 up the gauge and a load of air bubbles were released into the coolant. Must have been trapped underneath where the thermostat where the temp sensors are, hence the low temp reading.

With the card removed, temp now sits at about 1/3 along the gauge. I'll try and put it through a few more heat cycles in the morning, but it appears I may be on the right track.

I'll let you know how I get on

Forgot to say, both top and rad hoses are now hot, so definite progress being made. Amazes me the variation of issues and symptoms a simple air lock can give

If its an airlock then it will clear if you run it up to temperature with the heater on and the rad cap off; on these an airlock usually causes overheating.