Well, to tell you more. This car is only driven weekends. My wife and myself actually uses it to go to the mall on Sundays or just to go for a coffee.

What temp differences are there between the water entering the radiator at the top and exiting at the bottom? Maybe need to put one at the bottom but just a little colder.

You can get fan dangled in line switch holders. The only one on ebay is some gay buddy club thing. In the latest covs book there is a suttle davis craig unit for $19. would only extend a rad hose around 10-15mm! Thats the route im going.

And definatly put it at the top. Your temp guage reads temp at the engine, so you wanna turn your fan on at the right time according to that. also its hottest temp. after the rad it is much cooler.

i had the bung from a b11 sentra/sunny added to the older radiator in the same position as the sunny rad, lower right corner, yeah it doesn't trigger as soon as hot water comes out of the engine, but not sure you want that.

Having a switch that lets you force it on manually is good, but you don't want that as your only way to use it.

USE A RELAY!!!! or you will burn up the switch in the radiator and your fan will fail and piss you off..

if you can keep it under 100C then that is a good thing, you want it to get warm enough to get the oil to it's state change, and cook out the gas condensate, but there isn't really any benefit to letting it get warmer. A benefit to not letting it get up to 100C is hoses never burst, and you can drive home on a leaky radiator in a pinch.

On the US spec front wheel drive 310's (sorry, I don't know the vin number prefix) the "T" in the lower radiator hose had 2 holes in it, one for the heater return hose and a second for the thermo switch.

On my golf radiator the thermo switch is on the radiator tank that is in the center of the radiator flow wise. The golf radiator is a 2 pass cross flow.

I have a manual switch wired in parallel with the thermo switch so I can run the fan between runs to cool the engine down when I'm racing.

I think part of why the factory ones are at the bottom, is to keep the fan from coming on until the cooled water is such a temp, indicating that there isn't enough airflow on it's own, and needs more airflow. If the outlet water is cool enough who cares what the inlet temp is, it's going to be 40 - 60 F hotter if your radiator is working well. ( yes you want to monitor the inlet temp for your gauges, but the fan dont really care. ) I forget what the factory switch runs at 165 or something, which add 40 to that and it would come on about when the inlet temp is about 200F, using this setup and a 180F thermostat, which is also the temp oil coolers activate at the car never runs warm.

The factory thermal switch, which i use because they cost about $5 has worked fine for years.

i think of adding an override switch, overcooling before timed runs and freeway entrances had some benefits.

A slight twist on the adjustable Davies-Craig thermo switch.
I had a small copper tube soldered into the top radiator tank, with the inner end sealed off.
I slipped the sensor bulb into the tube, snug fit.
Then adjusted the thermo-switch to operate the fan relay when the in-car mechanical temperature gauge reached 95deg.C.
[This was with an 85deg.C. thermostat.]
I have it wired so that the fan relay always has power.
That way the fan will run after engine shutdown to prevent heat soak.
The advantage of this arrangement is that you can adjust the fan to operate at any temperature you desire, within the range of the thermo-switch
Has been 100% reliable and maintenance free

Thanks for all the replies. An update is that I decided to go for the top radiator hose.
A custom T piece is being made at the engineering shop that I will fit into the top hose so that the 1400 Nissan Pulsar (kicks in at 85 C and off again at 80 C)
can screw into the added T part.
I phoned around and no ajustable thermo switches are available here. This would have been a ideal thing.

Have a quick look here. for a budget setup.





For the moment, just run the thermo all the time. The thermostat will stop it from getting too cold.