The radiator was 3/4 blocked. After pulling off the top radiator tank and flushing it from the bottom water was only coming out of about 12 fins, 4 on the left and 8 on the right. The rest was blocked. Put a new radiator in and its back to normal. Thanks for the posts with some ideas and help.
So my navara overheated and i saved it just before serious engine damage. I pulled over and steam came out of the overflow tank. Temp gauge was almost at the limit. I let it cool, topped up with coolant and away i went no worries.
No idea what has caused it to overheat to begin with.
I took it...