If the engine is correctly tuned, is in good serviceable condition, & if the radiator is in good condition, it will not run hot. My GX never got over the half way mark when i had it in either the 1000, or in my 1200 ute [about 15 months]

I guess, if i was you, i might check the thermostat again. It was good 6 months ago, but that was then & this is now, & it's a low cost check.

I do not think that a shroud is necessary. They didn't come with one & it's absence was never a problem.

If everything else is proven to be good, then the radiator is the most likely suspect. At this point a replacement core is a recomended remedy. NOW, you gotta ask, "IF" i'm replacing the core, then how much extra for a heavy duty core. It's usually not enough extra to be a problem & if so, the extra protection it offers could well be a bargain.

I just picked up two radiators for my 1000 from the radiator shop. One [stock] was cleaned & tested, the other got a new custom heavy duty core. Total cost, $372.[Aus] The custom one was $327 & i regard it as cheap insurance. The other is a spare, or it is available.

Thanks for your comment again Dodgeman.
What I am thinking of doing is to buy a new termostat making sure the temp of it is right.
Putting it in and seeing what happens.
It is not too expensive and then I will know that I have a new termostat in also.
If it still runs too hot, I will look at changing my radiator.
Many told me here when I thought of a A15 transplant that I must just put in a triple core radiator for the engine.
Hell, if a triple core works for a A15 then it MUST work even better for a A12.
The radiator was cleaned up and when I sprayed the car 2 months ago I double checked to see how it looked.It was clean with no dirt or muck on top of the core pipes.They also flushed it for me when it was removed to spray the engine bay.It is just that I don't want to spend on a triple core and it does'nt solve the problem.Then I could have put in a larger radiator.It gets quite hot here during summer and I want to be save with temp on my engine.
To reply to cost, I have checked with a radiator shop.The cost of a triple core radiator is not too much.I am willing to pay the price.
It will however be too much if it does'nt work.

Have you got the Heater Blocked off ? Some times people block the heater off by joining the to pipes together with a hose .. This Causes the Hot water from the engine to go back into the water pump >engine.. without being cooled by the Radiator .. this causes the engine to run warm ..
If the Engine runs corrent Temp when moving over 60 km/h and hot when the Car is moving slow .. Air flow through the radiator is problem ... Cheers Cam

Nope.Heater is still like it came from the factory.Didn't change any of the piping.
Maybe I must do a test this weekend during the night when it is around 17 degrees celsius. I will drive at 120 to 130km/h and see if it still runs hot.If not, then I must presume it is the radiator.
What do you guys think?
I will go tomorrow with my car to the radiator shop to hear what they also have to say.
I phoned them this morning and the guy said I must bring the car and then they will make some measurements.

My 1200 ran at 3/4 gauge running at 100kmh
65mph through Arizona in august---115f
in the shade--My question is--did you remove
the thermostsat hoping the flow would cool
it off? the 1200 will definatyly run hot on the
freeway with no thermostat!!
Wubbits

Nope. I kept in the termostat.
A friend of mine said I must remove it.
I am totally against it.
The termostat regulates the temp.
I know it is working as it opens up when thrown in hot water.
It was tested that way 6 months ago.
From your comment I presume that the stock A12 radiator is not made for hot temp.
As mentioned we get around 34 degrees celsius during summer.
In the afternoon when I drive in traffic back home and it is so hot, the temp gauge goes just beneath the middle mark and stays there.Highway it starts to rise gradually to 3/4. If I put in a triple core maybe it will stay just beneath middle?
Or maybe I must fit a bigger one.
Is there any suggestions from you guys of a bigger radiator.
I do not want to get one from the wreckers.I rather want to let the radiator shop build a bigger one for me.
This is just my options that I am trying to keep open.
After all the tests have been done, I will make my choice.Depending on the test results.

For what it is worth, go see a mechanic.
My thinking would be that if it can handle high outside temperatures whilst sitting in traffic then the cooling system should be good.
The question then is why is the running temperature increasing at increased revs and speed which also increases the circulation of coolant & cooling air passing through the radiator & around the motor???
If it is not in the basics of points/plugs/timing/fuel supply etc. ( tune up stuff) then perhaps a mechanic can give further info or tests.

Quote:
you've answered your own question. at higher speeds, the car is under a constant load (wind resistance) and the coolant is circulating faster due to the relatively high revs these things do at highway speeds. So the engine is generating more heat and the coolant spends less time in the radiator and therefore less heat is transferred out, so the temp just slowly but steadily rises.

If the radiator was slightly bigger, you end up with a larger coolant mass to absorb the heat, and it spends more time in the radiator and therfore conducts more heat out of the coolant before it re-enters the block. The standard 1200 radiator is borderline in terms of size, and simply isn't up to the job at highway speeds in hot climates.

A larger radiator will be more efficient than a triple core radiator because more cooling surface is exposed to ambient airflow. The cooler the air passing over the cooling fins, the more heat will be conducted. By the time air gets to a third core it's almost as hot as the core's fins...

Besides, a slightly bigger secondhand radiator in good condition will cost about 1/6th of a triple row recore...

Wouldn't hurt to check the water pump before spending any money though. the impellor could be coroded, or have come loose enough on the shaft to slip at higher speeds.

L18_B110

The things you said is exactly what I was thinking.Namely, Water circulates to quick to be cooled properly for our heat.
I have the following stuff what I am going to do.
1. I am going to the radiator shop today to make measurements and talk to the guy.
He also mentioned some tests that he can do to see what is maybe wrong.
2.Buy a genuine nissan termostat and put it in.It will be relatively cheap.
3.I am then thinking of opening the cap of the radiator,starting the car and letting it idle to see how the water is flowing through at the top of the radiator.
Then increasing the revs to maybe 2 or 3000rpm and seeing if the waterflow is flowing quicker in the radiator.This way I will test in some way the waterpump.
What do you guys think of this idea?
This will give me an idea of the waterpump
I talked to my dad last night.
He said that in the 70's his datsun 510 SSS also ran hot on the highway when it was hot and his friends also complained about their datsun 1200 and 510's running hot.
He said they drilled a hole 1/8th of an inch into the termostat and it never happened again.
He also said in winter it didn't affect the temp on the guage.
What do you guys think of it

Nah,

It's likely not the thermostat. If so, you'd be running hot even on cooler days. If it is a poor quality one (or the wrong one, i.e. with a smaller opening), perhaps. Yes, I think it's worth checking to see if you have the correct one.

It's not the "circulating too fast" problem. A bigger radiator will make it circulate even faster (due to less restriction).

The common problem is that the original size radiator is just marginal. When new it was adequate, but as they get old (even when 'cleaned out') they are not quite enough for the job.

My 1200 ran exactly as did yours - on the warming trend on hot days.

How did Nissan solve the problem? Early B210s had a 1200-sized radiator. Later ones had a slightly wider radiator. It's a bolt-in and resolves the problem. Forget the expensive triple-core stuff. Just do what Nissan did.