I read an article in scc about the same car and problem. I would check these things:

1. check fan and fan clutch ( i could of swore that's how stock sr's ran)
2. check rad. pressure cap.
3. do you still have the fan shroud and drip pan on the car assuming you still have the stock fan?
4. check the temp sending unit.
5. if you have access to pyrometer check the upper and lower radiator hoses to see if they close in temp or
6. check radiator (with engine off) for cold spots in the core. this is to see if the radiator is plugged.
6. if you have electric fans check to see if they come on at the right temp/ time, relays etc. these are some of the things off the top of my head. if you have the front end that I think you have there is not much to be had as far as air flow. if you want to read more about the Scc article go to www.SportCompactCarweb.com and look for project silvia. In one of the installments he talks about his delema of overheating and his fix.

hey guys sorry to ask a 180sx question but it's the same thing, and the guys on nissansilvia arnt so trust worthy in their answers sometimes

my 180sx doesnt overheat regularily (driving around town) but on the rare occasions i go somewhere down a freeway or out bush and sit above 90 km/h it starts over heating, the faster the worse it gets

the best way to cool it has been to actually stop the car and let it idle, or reduce speed below 90 for a while and the temperature will drop

it will overheat when cruising or driving hard above 90km/h

i removed my numberplate as it was blocking some airflow... no change

i put the heater on full and this seemed to keep it at a normal running temprature, though turning it off it started over heating again

seems odd... just finished checking the thermostat, at $50 for a new one i decided to just test mine, raher than replace anyway

i put it in a cup and poured in water from the kettle, and it slowly opened up. seems to be working fine

any suggestions on what the cause might be, i haven't come accros this problem before