td27t overheating

Hello,
Can anyone suggest an answer to the following problem in a '91 pathfinder? Coolant temperature normally runs just under half way on the gauge but recently at highway speed the temp began to climb to the gauge mark just below 'H'. Reducing speed and the temp fell but again climbed as speed increased. Replaced thermostat and flushed out radiator but can anyone suggest anything else? BTW when the engine is hot and turned off I could easily rotate the radiator fan but the radiator itself looked clean....
Many thanks, Andrew

What about if you are traveling slower but in a lower gear so rpm is the same?

You would think that at high speed the wind should be enough to cool the radiator. The fan is on a hydraulic clutch that kicks in when the engine heats up. They can die and yours is old enough. Not sure how you test that but if it turns easily when the engine is hot it might be a bit sus.

Best to say 91' Terrano as the Pathfinder is only ever petrol.

What part of the country are you from? Hot? Humid? Dry?

Could be one or a combo of many problems, here are the steps I'd take in order (you've already taken some of them) and test to replicate problem after each step. None of them are Nissan specific.

1. Check fan shroud for damage.
2. Flush cooling system and replace with quality coolant
3. Replace thermostat.
4. Replace thermostatic clutch.
5. Replace water pump.
6. Have coolant system tested for hydraulic blockage & pressure
7. Carefully inspect radiator for air-side blockage.
8. Replace thermo sensor (multiwire one, not the single wire one for the glow control)
9. Fit thermo-fan/s.
10. Replace radiator with performance aftermarket unit.
11. Fit rear-facing bonnet scoop.

Hopefully you can knock the problem down at no.4 or 5.