Nissan put them in the bottom hose.

There were two different temperature switches for the bottom hose location:
* 21595-M0206 SWITCH-THERMOMETER ON 85-90C
* 21595-M4961 SWITCH-THERMOMETER ON 72-75C

Top pipe is better.
It will then pick up that the water coming from the head is too hot and switch on the fan. The bottom hose is water coming from the radiator that has already been cooled. If this is still hot enough to switch on the fan if the switch is in the bottom hose, it might be already too hot for the engine.

@1200rallycar

Sorry, I just bought it at our local parts store. Don't think the partnumbers will be the same as on your side. Just ask for a Nissan 1400 Pulsar thermo fan switch.

Ok, I ran into a bit of bad luck this weekend. I installed everything. I used some loctite on the thread of the switch and tightened it up so that the O-ring seals nice and relatively tight.Left it like that overnight and sunday afternoon I filled up the radiator.Started the engine and let it idle. At about precisely halfway I started to worry because the fan did not kick in yet. Spoke too soon. Exactly on the halfway mark on a stock datsun temp gauge and stock datsun temp sender unit fitted, the fan kicked on. So, to inform everyone, 85 C is at about precisely middle on the temp gauge. It ran for about 2 minutes and the needle dropped about 1 to 2mm and the fan switched off. Very happy about it. This was done without the radiator cap fitted so that the air bubbles could escape that could have gotten trapped in the system. Ok, now the presure test. I fitted the cap and would you believe me that there is a pin hole smaller than a hair's thickness that the missed in welding the T piece.
If I wipe away the radiator fluid from this hole with a tisue it take about 1 minute for a new one to develop.

A question. I want to take it to a exhaust shop and ask them to just spot weld the hole with a CO2 welder. Will it not damage the sensor due to electricity going to flow through it when welding?
Heat I am not so much worried about as it will be just a quick spot weld job on the hole.

take it back to the engineer and tell him to get off his ass and learn to weld...

TheA14 powered N10 Pulsar has the same sort of set up standard Its mounted in the side of the engine bay and is fitted into the bottom hose. could work out cheaper than getting one made.

Well, the switch was R77 South African rand and the engineering of the T piece was R280 South African rand. Damn expensive and not even stainless steels. Not worrying much because the one T piece I removed from the bottom pipe only had surface rust on the outside and none on the inside. Is in the car for 2 to 3 years now.Will clean them up and spray them with some spraypaint on the outside or paint them with some heat resistant paint I have at home.Apparently the heat resistant paint sort of penetrates the metal.

looks great!

im getting one of these instead of an adjustable probe one now, will be uch neater and reliable i think

i would say you need to tighten it down to the o-ring

do you have a part number for that switch?

wait what am i talking about..

megasquirt is going to control my thermo now... hehehe

i already have a temp sensor tapped into the head for that