Tm 150 coolant levels

[agrotron]

I have got a new to me tm150. After a couple of hrs hard work the coolant level light start to come on, intermittent at first but can then stay on. I checked the coolant levels and it dropped to approx an inch below the cold fill level. It doesn’t overheat though.

I changed the radiator cap as suspected it could be this as rubber seal was perished. Got a new genuine one and it looks like the water could be coming from the cap. Should the cap vent if to much pressure or should it vent via the expansion tank? The cap says wearing 22psi but it doesn’t have a spring on it and the it doesn’t block the overflow to the expansion tank so suspect the expansion tank lid is set to vent at 22psi?

I noticed if I rev it flat out the expansion tank level can rise by approx an inch but no bubbles. (Hopefully it’s not head gasket)

Also the next to the temp sensor there is a pipe the has been blocked off with a bolt. Where should this go or should it be blanked. Pic below. Thanks for any suggestions.