I am about to tap a temperature switch into the top of the thermostat housing on my 200tdi. The switch is rated for on at 92-87 Celsius and is from some sort of family car.
I want to have a switch to turn on an electric fan via relays while retaining the temperature sender. Does anyone know if this temp range is enough? and is there an alternative method for doing this?
Also this engine is in a series.

The purpose of the fan is to provide extra cooling if the water temperature AFTER the radiator is too high. So the best location for a temp switch is after the radiator. If you locate the switch in the thermostat housing the fan would switch on too soon. Some people use a kenlowe probe with mercury in it. But this is not the most reliable solution. The switch you have is a good solution. In your case a piece of pipe with the same outer diameter as the inside diameter of the outgoing rad hose would do the trick. Drill a hole, weld a nut on it with correct thread to fit the switch. Cut the rad hose and fit the piece of pipe with jubilee clips. Do the wiring to the fan and place a relay. Current to start the fan can be high. Don't forget a fuse. On this site (X-eng) you find the schematics to wire it up.

I did the same, except I used the x-eng solution with the sender and adapter. My thermostat is a 88 degrees one. Fan switches on only in extreme temp. situations. Had the kenlowe probe before this setup and almost overheated my engine because the probe failed.

Hi there has any body got any ideas I have a 200 tdi. In my 90 which was a petrol ,the temp gauge doesn't read the sensor accurately , other senders thread is different ,so if I put a diesel temp gauge in would that work ?

I used the mechanical gauge from TIM (Tim Water Temp Temperature Gauge 52mm Complete Kit Inc Fittings & Pipe Tim005 | eBay

works perfect, I had a problem with the resistance of power supply in my dashboard

Thread of def 200tdi is (I think) is 5/8 UNF

hi if temp swich was fited to rad on the donor car then it would swicth in to soon. if it was fited to the therastat housing then it should work fine

I have mine fitted in top hose with an xeng adapter set points of my switch are 83/87 and 87/93 I use the lower one to switch the fan on and the higher one to light a flashing LED on the dash [series 3 ]
The 200 stat opens at 88 but fan does not operate so suspect stat opening slightly earlier.
I will wait to the summer to see if I have tomove switch to bottom hose.
Note the switch was fitted in top hose with 2.5N/A diesel and was working fine there would come on when loaded in warm weather or if pushing it hard up hills.