The engine temperature is going up to 3/4 when the engine is running whilst stationary

Maybe start with these 3 things: First verify that your radiator fans work. Since the car is already overheating, the fan or fans should come on as the temperature rises. The fans are supposed to come on after a certain temperature is reached, like when idling in traffic on a hot day. That temperature is higher than normal operating temperature by several degrees, so you need to verify the fan circuit is working, that the fan motor is good, maybe test the fan motors with jumper wires if not sure.

Second, You maybe should perform a simple pressure test of the cooling system. It is a sealed system under low pressure that helps to keep the engine from overheating. If it doesn't hold pressure, it might be leaking out somewhere, and that is definitely a problem that contributes to overheating. A shop could do a pressure test in about 15 minutes if the engine is already warmed up, so it should not be an expensive test.

Third, along with the pressure test, you also should do what is called a "block test" of the coolant system. This helps determine if a blown head gasket might be causing overheating-a common
cause of overheating. This test checks for exhaust gases in the coolant by turning a test dye a different color if exhaust gas is present in the coolant. This test is also pretty simple to perform, but a special tester is required which any shop should have. It should also not be expensive to have done-it only takes about 15 or 20 minutes.

If the fans work as they should and the coolant system holds good pressure and no exhaust gases are found, then you have to keep looking-maybe a water pump that doesn't circulate the coolant good from having badly worn impellers, or maybe there is some blockage in the radiator preventing circulation. A worst case scenario would be a cylinder head that has a flaw, like a broken or cracked assembly. Many possibilities. Also, if coolant is old, a good idea to replace it with new coolant, and a new thermostat, and possibly a new radiator pressure cap. If old coolant is dirty or sludgy looking, the system should be flushed. Good luck, I gave you a lot more than one thing to check, but overheating is so serious, you really need to find the problem before damage occurs.

2.9 to 3.9 bar at 3000 rpm is fairly general for the Nissan range including turbo diesel, though the pressure isn't listed for the td27 engine. I doubt it would be more or less than the others.
I notice one Nissan commercial vehicle engine where 3.0 bar at 2000 rpm is specified.

The oil pressure test should be carried out at normal operating temperature.

Did you have the head checked for warping and crack tested. because combusting gas is finding its way into the cooling system. have you replaced the thermostat .

have you located the leak? is it leaking out of the engine or into combustion chamber? go get the cooling system pressure tested when the pressure is up on the gauge of the tested check all hoses pipes and sensors in the cooling system if there is no visible leak have a block test done this checks for hydrocarbons (unburnt fuel) in the cooling system if this is a positive test you have a head gasket problem. o had a customer with a 2008 Mitsubishi that had a leak and it was not visible when the engine was cold or warm it would only leak whilst the engine was in the cooling down stage with out the engine running it turned out to be the head gasket. don't forget to check the carpet in the vehicle for water ensuring the heater matrix is not leaking

If the belt broke when engine was running, stationary or moving, you have the possibility of bent or broken valves, or piston damage. Hard to say without pulling the head off, although you could remove the valve cover, and watch the valve train movement while you turn the camshaft by hand. If it seems okay, you could try a new timing belt on then turn the engine by hand several revolutions, listening for scraping noise or crankshaft locking up. Either would verify damage. If crank turns free and no noise, do a quick compression test of each cylinder. If compression is good, you may have dodged the bullet!

Run a cooling system pressure test. If you are losing pressure, then you will have to first locate the source of your leak.

With the engine started and the radiator topped off with coolant, does the radiator spout water out of the top? Does the spouting become more aggressive with engine revs? Yes? = Blown head gasket, or cracked cylinder.
No?- check operation of radiator cooling fan. With car stationary and hood up, run engine up to temperature and make sure radiator cooling fan kicks in before the engine temperature rises too high.

If there isn't a puddle of coolant forming on the driveway after the car sits for awhile and there isn't a puddle inside the passenger compartment, then the problem must lie in the cylinder head or engine block.

you need to replace the heater core and pressure text the radiator cap, replace if it leaks down go to a parts store to do this also you need to replace freeze plugs if you don't they will blow and ruin the engine,a slo check that the water pump is not bad, loosen the pump belt and see if you can wiggle the water pump with fan connected, if you have any play replace the water pump. and add new anti freeze.

Pressure test the system, it sounds like head gaskets that is backing into the water jackets and not the oil ports, which is the best of the two. Have heads checked for cracks of warping.

if you see the water leaking form the front side of the engine usually from the water pump since the pump is not running you also wont get heat, bit when you pressurise the sys you are forcing the hot water into the core and you have heat, it is the water pump.