[v12-engine] Temp Senders

Date: Sun, 16 Jan 2000 10:55:25 -0500
From: “Kirbert” palmk@nettally.com
Subject: [v12-engine] Coolant Temp Gauge Senders

Here’s what I know:

The sender in my '83 has no P/N on it, but it quite probably was the
original sender. It does say “Smiths Industries”. At 19�C, it
measures 863 ohms. At 40�C, it measures 412 ohms. In hindsight, I
wish I had heated up the water more during the measuring and gotten
data all the way up to boiling, but it’s back in the car now and I
ain’t taking it back out just for that.

The specifications sent to me for some aftermarket senders include an
item 320.010, listed as having a temp range of 50-150� and a
resistance range of 323-18. I’ve been told that this means it has
323 ohms at 50�C and 18 ohms at 150�C.

Yes that is correct

Here’s what I’d LIKE to know:

How well would sender 320.010 work connected up to the OEM temp gauge
in the XJ-S? Offhand, it looks sorta like the correct range of
ohmage. I suppose what I’d need to do is connect some example
resistances in place of the OEM sender and see what the gauge reads.

Here’s why I’d like to know:

The 320.010 sender is an M12 x 1.5 thread. That means it would screw
into the same port that the EFI coolant temp sensor fits – which, in
turn, would mean a gauge sender could be installed in the left
thermostat housing without having to do any drilling or tapping. Of
course, another place would still need to be found for the EFI
coolant temp sensor, but one problem at a time.

Sounds good to me.

The simplest thing to do is to go to your local electronics shop and buy a
500 ohm potentiometer - they are cheap maybe $1 for carbon a bit more for
wire wound. Wire wound may be better - less susceptable to burnout close to
the very low ohms end of its travel.

This thing is a variable resistor 0 - 500 ohms.

Just remove the wire from the temp sender on the car and connect to one end
of the pot. Connect the middle leg of the pot to earth on the car.

With ignition on you will be able to vary the potentiometer and see the
temp gauge in the car change.

With an ohm meter measure the resistance of the potentiometer at varying
points on the temp scale and make a note of these.

I would suggest measuring the resistance with the Temp gauge indicating at
each mark on the gauge ie C NORMAL H.

Now for any temp sender - suspend it in a pot of water on the stove and
while measuring its resistance slowly increase the heat.

Note the readings every 10 degrees to boiling.

Plot resistance against temperature and then for any resistance you have on
one side the temperature that brings the sender to that resistance and on
the other side you have what the gauge will indicate for that resistance.

So now it does not matter what sender you use - for any indication on the
temp gauge you know what temp causes it for a particular sender.

Peter Cave
Brisbane Oz