Auxillery water temp guage and where to fit the probe 100 series

If it is a low coolant level alarm it's the best place for it, no problems.

If it's a coolant temp gauge it should have the sensor bolted to the engine, I used a bolt on the housing for the top radiator hose on the head, If it is in the top tank of the radiator and the thermostat fails to open it wont register the heat in the engine, or if you lost coolant the temp. would drop.

I have re-powered my HZJ75 series with a 24 valve turbo engine ex an auto 80 series. I have had a low coolant alarm fitted to the top radiator tank for some 4 or 5 years and an extra coolant temp gauge is installed in the top outlet housing from the engine to radiator. Because the engine was originally from an auto vehicle that housing has two sensors already fitted. One was to shut off the air con if the coolant temp got too high and the other apparently limits transmission upshifts in certain engine temperature ranges. I removed the auto limit sensor (my vehicle is manual) and tapped the hole to take the gauge sender. I left the original temp gauge connected and both work quite well. With your vehicle I would think you could have the gauge fitted to the top tank, my level alarm has never caused any dramas, or maybe drill and tap the coolant outlet housing.

Cheers
Pop

Hi Jacent,

I take it that this temperature sender has a "bulb" with a 1/4" threaded connection?
Positioning the temperature sender in the the radiator tank is not a good idea. I frankly do not believe your auto sparky is correct about "all the mining cars" etc. He is probably looking for an easy way out.
1) The purpose of the gauge is to measure the engine temperature not the radiator temperature which may not be the same thing. (e.g. prior to the thermostat opening during engine warm-up or in the event of low coolant.)
2) Attaching to the radiator tank is not simply drilling & tapping the tank. If it is a metal tank it is too thin to tap and it is necessary to drill & solder on a threaded boss to accept the sender. If a plastic tank, it will not reliably take a thread and it is necessary to fit a boss with a locknut inside the tank... a difficult procedure. If you elect to fit the sender to the radiator tank you would be wise to have it done by a radiator specialist, not an auto electrician. The outcome of a poor fitment could be disastrous!
3) It would be more appropriate to position the sensor into the water jacket of the engine. There may already be a suitable location available, currently closed with a threaded plug or suitable for drilling & tapping. An engine mechanic could advise you about this and you would be wise to obtain his (or hers, lol) advice.