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

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.

had similar problem with the sedan, ended up being radiator cap... replaced that and have now found that when the radiator shop rewelded the top tank back on, 2 of the welds are a bit thin and are leaking under load (dont ask how i tested this but it did involve driving the car)

a slight mist would come out and the fans would disperse it through the engine bay.

If it still does this after they fix it on monday, its either the bottom hose collapsing or water pump is shot....

should be very similar on sr20det.

My solution to you, sell the 180 and get your $$$ back. then you can drive the mrs coupe for a daily.

Blocked radiator.

well it's not the cap either, changed that with no success (unfam you owe me $15, lol jokes)

must be blocked rad as said, only that or the pump left, but it keeps it's cool at low speed so must be blocked rad....

GOOD news i've got the same problem with my 120Y try the water pump, it might look good but it might not be try pulling it apart and putting it back again. if new one needed try repco.

My old 260Z was doing the same thing. It ended up being a seized shut thermostat. The car was only being cooled though the byepass hose! It was fine at idle, running around town etc. but as soon as i got on the freeway it would get hot!

So your rad could be blocked. get it to operating temp and feel the top rad hose, then the bottom rad hose. If the bottom is cooler your rad is blocked! Or look at the rows inside theough the rad carp hole. is there any #### stuck in there, blocking them? Take the rad to a radiator shop for a flush out.

Its not the fan/s. Fans dont come on at FWY speeds, only when your going slower/stop starting. Which is when his car runs cooler.

radiator is blocked or your clutch fan (if it has one?)
spins too easy at higher revs not pulling the air through

My 2 bobs worth ....
wont be the clutch fan, as the problem would be reversed. Clutch fans are meant to pull at low revs and not at speed. I would look at the radiator. Working at lower speeds but when you push coolant through at higher velocity and temp - the radiator cant remove enough heat in the shorter time and higher temp. Flick the radiator - if not cured then you still have a new radiator Good luck!
Cheers

I had a Skyline (R32) that would unexpectedly overheat - my problem was the thermostat would get stuck shut, then open suddenly and 20C water would meet 120C water - steam would piss out everywhere and the temp would go from C to H in about 2 sec flat....so if you don't have those symptoms and also the rad doesn't seem to be losing fluid - i'd bet on blocked rad too.

Some place will test them for nothing (if you pull it out of the car). Auto Cooling in Clayton did that for me - real good guys there.