Hi all

As some of you might know, I have installed my thermo fan and removed the stock mechanical fan. Now I am puzzled as to where is the best location to put the thermo switch that will activate it.
I already have at the bottom hose a stainless steel T pipe that connects the hose coming from the radiator and the hose then going into the engine block.The other T part then is to connect the flow from the back of the cylinder head. I want to take this thing and just let them drill and weld a nut that has the correct thread for the sensor to the opposite side of the T that goes to the back of the head.

Some people say I must put it at the top hose. Currently this hose has a obscure bend to connect it without collapsing on itself. Now to put the sensor in here and also keep the bend going, I will have to make a stainless steel connector with a 90 degree bend. On this bend I will let the engineering place weld a nut that have the correct thread for the sensor.

My problem: Lets say the normal radiator pipe's inside diameter is 40mm. I am now going to put a 90 degree bend in this pipe and this internal diameter will be about 30mm. So this will cause a partial obstruction (90 degree bend and a smaller diameter in this stainless steel bended pipe)in the flow from the engine to the radiator.
Will this not cause maybe some flow problems?

I'm pretty sure you have to put it in the top hose, as this is where the hot water from the engine enters the radiator. I guess you might be able to put it in the hose bottom hose if you can set it to activate the fans at a lower temperature, but i'm not 100% sure.

To be honest, I want to fit it in the top hose because it will read the water as it comes out of the engine.
My problem is just that I will have to put a stainless steel 90 degree bend in there and it will also cause a restriction due to the hole inside of it being smaller than the radiator pipe's inside diameter.Worried that it would cause restriction and cause overheating or not flowing correctly.

I would still suggest that the best place for the sensor will be on the cylinder head.

I'm pretty sure that a even a fully open thermostat would be more restrictive than a pipe that fits inside the hose, which i'm guessing would be about the same size as the hose connections on the radiator and engine anyway. I don't think it would cause much of a problem.

My 2c if I may?

I agree with dat141, the thermostat is going to be one of the biggest restrictions in the cooling system. The solution you're thinking about doing shouldn't be of a concern man.

To see a fully open thermostat just put it on the stove in a pot of water and heat it up to get an idea of how much/little they open.

A nice bend piece of stainless as a top radiator hose would look really good too, bit of bling even.

Yea, I also thought about the thermostat.
Maybe I must do it and just see what happens.But as mentioned I think the thermostat will cause a bigger restriction than my 90 degree bended pipe with a little smaller diameter than the normal radiator hose.

Can you believe it. I am struggling to get a decent pipe that are 90 degrees and modifyable with regard to welding on a nut for the thermo switch.

The engineering shops are also charging a arm and a leg for labour to make me a custom one that will fulfill my needs. I am in a hurry with this project so I think for the time being I will install it on a switch to turn it on and off manually.

Does anyone know where would be the ideal time to switch on the fan?
Meaning when the needle is where on the stock Datsun temp gauge.
For example, where on the stock temp gauge is + - 86 degrees celcius.
I would think just underneath the middle mark?

hmmm using a manual switch for your thermo seems fraught with danger. I have done it once to limp home my old 4wd, but I wouldnt reccommend it for daily use. You get distracted once and it could be too late for the ole a series.....
When I fitted the thermo to my patrol, the fitting kit came with a rubber shim that you put between the inlet pipe on the radiator and the hose. The sensor sat between the two like a sandwich. No screws in pipes. simple really.
Since I gather that yours has a threaded sensor, you either have to go down the custom pipe road like you spoke about, or tap into the top tank on the radiator. This will achieve the same effect as in the top hose.

about the time to turn it on, well I just did mine be trial and error. I had it turn on early, tried that, and just adjusted till i was happy with it and it never failed, the thermo setup that is. the rest of the car.... well its history now thank god.