Hi guys. I've had a non-functioning temperature gauge in my Datsun 240Z.
In this episode I'm gonna do some diagnosis.
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So the temperature gauge in the 240Z. It's a fairly simple unit. It's a gauge
and a thermal resistor on the on the engine.
There's no means to calibrate the gauge it is just fixed based on what the
thermal resistance the produces. A thermistor is a device which its
resistance greatly decreases with an increase in temperature. In the original
240z once came out with it was a two-piece unit which is a little pill
with the clip that, you clip the wire that runs to the temperature gauge on it.
It has a hollow nut to hold it in place. The thermistor is very simple. It relies
on a ground through the engine and it is simply a resistor. So the diagnosis. The
two ways to check it is...There two, there's only two paths that will be
wrong with this system and that's the thermistor at the engine or the gauge. A
way to check the gauge because the thermistor as it increase in temperature
tends towards no resistance is you connect the wire that runs from the
thermistor to the gauge to a ground which essentially has no resistance
which means the temperature will be off the charts and if you do that and the
gauge deflects to all the way around it's unlikely to be the gauge that's the
problem and it's likely to be the thermal resistor. The thermal resistor
can fail because it is a resistor subject to temperature hot and cold hot
and cold expanding and shrinking over the span of nearly 50 years and if it is
the original one and they can wear out. So first thing I'm gonna check is I'm
going to ground the the lead at the thermistor and see if the gauge to flex
and if the gauge deflects well then I will just replace the thermistor. I'm over
here at the thermostat housing if you know your Datsuns you'll know that this
thermostat housing this lower half is definitely not 240Z
housing and you're correct. This is a 260z 2+2 housing which i pinched from a
76 model that was automatic. Key differences are is this blanked off bung
here and this large hole here which I believe is an M16 with a 1.5 pitch
thread. In this instance for this car I'm utilizing it for a thermal switch to run
the thermo fans. So anyway this is where the thermistor lives. My wiring is a
little bit different from standard but what we're going to do is we're going to
ground this wire onto something and then we're going to turn the key on the
ignition and see if the needle deflects. But you can see that's the hollow nut
that holds the thermistor in. Don't mind this corrosion that that occurred
very early on and I've been too lazy to clean it up it's it's a it's been fixed.
So there's no leaks. see yeah we'll ground it out on
something. so I very simply just grounded my frayed wire which I will fix up
eventually I've grounded it to the housing for my ignition coils. So we're
inside we'll just flick the keen we'll see if the temperature gauge goes around.
Oh well, it's going going going going I better turn that off. If you can do that don't
leave it on too long because if there's no resistance feeding that temperature
gauge this temperature gauge will draw a lot of current because there's nothing
stopping it and if that happens you chances are, you know, if you whatever you've
grounded with could get very hot and could get could melt. So yeah, if you're
gonna do it just flick it check its movement don't leave it turned on
otherwise you could end up with a catastrophe on your hands. That was lucky.
It's very clear that it's not the gauge and it's is thermister that's the
problem. So I'll look at getting a replacement unit I believe there are a
few manufacturers that make a one-piece unit as opposed to the two-piece. I'll
have a look around for those I think I'll go with that there shouldn't be too
much in 20-30 dollars or something that.
If I do find one I'll throw it in
the description. If you found this video useful if you're doing your own 240Z
temperature gauge diagnosis appreciate a thumbs up. Have a look at all the other
videos I got on the YouTube channel and if we're meeting the first time
consider subscribing so thank you catching the next vid!