Have you had the cooling system pressure tested to rule out a faulty head gasket ? Could be faulty thermostat, blocked radiator, as for head gasket always go for genuine and it is identified by the number of notches it has cut out on the edge.
Definitely thinking head gasket as I tried to bleed the system and when it got up to temperature I could smell diesel fumes/burnt oil
And for the gasket if it has more notches on does that mean it’s a better 1, or do I have to take the head off 1st to find out which I need sorry for sounding dumb
Sounds like the system is being pressurised had it with a Terrano engine with a recon head that was supposed to be new but i was lied to as it was not skimmed had it skimmed and all the symptoms you described went away
Looking from the front of the engine the gasket protrudes at the left rear side and back you should be able to see the number of notches and this is to determine the thickness of the gasket, the number of notches are from 0 to 5 there will be notches on the side and the back of the gasket where it protrudes, it will be worth changing thermostat aswell as an engine coolant flush.
Coolant and combustion gases mixed together can produce foam is that where your smelling the diesel fumes /burnt oil have you checked the dipstick and removed oil cap to see if oil is milky or like mayonnaise?
It does look like the combustion gases are producing bubbles/foam in the coolant, this can be caused by the head gasket failing or worst case scenario a cracked cylinder head, this can be checked with a combustion leak test kit.