Pressure in radiator when cold? 4D56

[Gavgav238]

I had a second hand engine fitted after my last one failed and it now seems to always have a few air bubbles in the radiator when bleeding the air out with the radiator cap off and if engine has been run and left overnight the radiator hoses are still firm from pressure?

If it was a head gasket failure should the pressure leak back into the exhaust over time or would it just hold the extra pressure in the cooling system?

Any other possible reason anyone can think of?