Radiator overflowing ,spurting

[Voycey]

Hi Water spurts ,sometimes, out the cap on the radiator of my 36 when it gets to operating temp , on the gauge, it never seems to overheat, and the temp fluctuates from idle to moving. From previous threads others state the radiator water level will find its own level depending on running temp etc

What is the best way to check that both water pumps are working properly.

Could the spurting be a semi blocked radiator , dodgy cap seal or something more sinister.

Appreciate any help.