ok heres the symptoms:

when car reaches opperating temp. its fine 175 deg f therostat opens at 180 f and then it drops to 175 f again.
Driving in open road its nice- stays at 175- 180deg f in 20 - 30 deg weather.

Stuck in traffic or stop start driving just slowly climbs (as expected) but it never exceeds 190deg f.

Lately it can go as high as 200 deg f and even 210deg f on one occasion when stuck in stop start traffic.

This would not be a concern as it did this last year when it was 35 deg plus celcius.

Temperature at ambient has not yet exceeded 25deg c when ive driven it.

As the thermo stat opens and closes when reaches idle and when driving i can pretty much rule it out i figure.

My other 2 options are:
1. water pump(but then it wouldnt be cooling or pumping when moving as well cause it wouldnt be pumping water then either)

2. air flow. Weird thing is clutch fan seems to be working at idle but not sure what it does in traffic(should be same as at idle- unless when it heats up in engine bay some how it stops working and just free wheels- they are internally temp regulated anret they- viscious oil or some thing.)

what to do? this rad even kept anges rotor cool once upon a time so im a bit perplexed.

I could swap a a12 water pump into it and the stock non clutch fan, but not sure if that will fix it.

Any ideas out there?

the core in the rad might be blocking up..
doesn't take much...

damn it, wonder with what, it is a pretty thin core, but nice and big.

Some of that nice 30year datsun cooling system rust. yum

Yea, I agree. Can be starting to clog up.
I had mine re cored a while back and just last weekend I checked into the radiator cap with a flashlight to see how the cores look. I just hate that they are such thin pipes.
They have small stuff that look like old rust particles partially blocking some of the core pipes. I just hate this small flattened pipe cores.

What radiator do you have in currently?
When I get it cleaned in the future again I will use that trick Dodgeman mentioned of cheese cloth in the top pipe for a couple of weeks to catch the crud that would possibly have started to block the core again.

I use Auto Cooling in Clayton, (probably a bit far for you Mik) but for $40 he'll acid dip it and let it soak overnight, then flush it out and respray it black. Pretty cheap.

Last one I had done was the 'rana rad - was $75 but that included pulling off the top tank and rewelding it on again.

A new core would be more like $200+ out of interest.

could the fan be on backwards? i've used auto cooling for lots of datsun and other stuff, good blokes. Mildman, how's that CA conversion going?...

Having some ebay trouble re my intake piping, once thats sorted I've just got to knock off some wiring....hadn't touched it for almost 1/2 a year now finally getting back into finishing it (new baby in the house and I spend a couple of months OS...there my excuses anyway)

Looking forward to hearing it start soon.

ok i might swap in the ca radiator but need to make an extension pipe for bottom tank as it s on opposite side.

would galvanised pipe do the trick? only need about 10cm of it.

It could be anything Mik. How old is the thermostat. Even new ones have been known to fail. Even the radiator cap not holding enough pressure can cause overheating. Too many variables. Although radiators can block up over time, the way to check one is to measure the temperature over the entire radiator and check for cold patches. Another thing is that the way you piss around with the tune of your engine a while ago it could be that the LPG is running a bit lean. LPG combustion temperature is much higher than petrol. LPG engines as a rule run hotter than petrol anyway. By at least 10%.

Yes, could be anything. Easy test is put the stock fan (non-clutch) back on. Work better?

My radiator was heating up more than normal this past summer. I took it out and spent two hours pulling pine needles out of the fins, and straightening the fins. But now it's too cold to tell if it makes any difference...