Cooling systems are one of those things that we seem to take for granted & we neglect them at our peril.

When I got my 1200 coupe it was clearly in trouble in the cooling department & if it wasn't for a strong headwind & constant light rain I would have suffered quite some grief on my trip home with it.

I brought all my unknowns under control by replacing all the rubber hoses, including the heater hoses as well as the water pump [loose bearing] the fan belt [it was inexpensive] & the thermostat.[I didn't like the look of it.]

The radiator core was clogged & was replaced. I removed the block drain plug & got stuck into it with a long thin screwdriver to dig out as much crud from the block as possible, flushing it all the while.
The heater got a reverse flush too & it works a treat.

It was finished off with a cheesecloth condom type of coolant filter in the top hose fitting & the only problem I suffered since was about 3 weeks back in Victoria while driving in that "devastating heatwave" with 44C temps [112f] A faulty thermostat raised the coolant temp to the 2/3rd mark but this has since been rectified for the sum of $16 for a replacement.
It has otherwise always run with the needle right in the middle of the guage at all speeds & in all temperatures & still does now.

Take care of your cooling system & it will take care of you. Neglect it & you could be up for a replacement engine as well as the cooling system repairs that should have been done earlier.

gemini radiator wasnt that hard was it, now time to try the n13 pulsar/s13 set up... things get interesting there

good to hear ytou fixed it

Just an update on how this turned out: I replaced the broken thermostat and tried it out with the old radiator. It did not really seem to make a difference (maybe a little but not definitive). I then put in the gemini radiator and it now seems all good.

I was surprised the car was only running a bit hot (2/3) with a physically broken thermostat that was decidedly stuck closed, and that replacing the part did not seem to make a difference.

do the gemini rad swap while your at it- save that boiling water to heat the hoses so they slip over the rad inlet and outlets- or microwave the hose for 3-6sec to soften it up slightly.

Excellent. It's an easy solution.

With the crumbled fins it still may go past the 1/2 mark occasionally but that won't hurt anything.

I just pulled the thermostat and chucked it in boiling water. I did not observe any change as the water got up to boil. The thermostat also looks broken - cracked along the top - so I guess its stuffed.

install gemi one, while your at it do the thermostat too with a new one.

should be fine, if not will need further investigation

I had the same with mine when i had the standard A12... The thermostat was faulty along with a faulty temp sender.

To test the water pump:

1. Check for play: remove the fan belt then see if you can rock the fan back and forth. There should be zero play. If the bearing is worn it should be replaced before it starts leaking.

2. Check for leak. There is a weep hole on the bottom of the shaft area if you see leakyness there replace the pump



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Just have the heater valve open... should do the trick