Pressure in radiator hoses

[Casheye]

Hey Peeps,

I'm trying to diagnose an issue with building pressure in the top and bottom radiator hoses. It feels like there's more than would be expected.

If I run the engine while parked, the temp builds up as expected and the hoses stay pretty malleable but for a while the hoses have had almost zero squish in them after a short drive.

I've put a sniffer on the expansion tank which came up fine and there's no sign of anything suspicious and the oil in the head and sump (it's black and not like custard)

I used a bottle of wynns flush and then a bottle of leak stop just in case and it's got a fresh batch blue Ethylene Glycol coolant and there seems to be more squidge in the hoses but that could just be me hoping something's different.

It runs and drives absolutely fine.

I've ordered a inline T adapter for a Stack mechanical temp guage which I'm going to use to see what temp the coolant is getting to as I know the volvo one in the cluster isn't really helpful on that front but is there anything else I can look at to find out why this might be happening?

Cheers.