300tdi temperature gauge

drfoster · Mar 27, 2024

Hi there,

my temperature gauge on my 110 300Tdi is reading 0 even when warm, only happened in the last few days. i have disconnected the wire from the sender in the thermostat housing and put a multimeter across it from the cable to earth and its reading 12v, but when i connect the multimeter from the wire to the middle pin on the sender it reads about 8.5v , i assume it changes according to the temperature being sensed.
The circuit seems really basic so not sure whether the sender is at fault or the gauge itself. any pointers on what could be wrong and is there a good way to test the gauge itself?

cheers

Steve

julianf · Mar 27, 2024

Iirc the sender is just a temperature dependant resistor. I think it works by sinking current from the gauge, through the sender, to ground (negative).

There's one wire to the sender as it's grounded through the housing / body, back to the battery negative.

To test the gauge, apply +12v AND some gauges themselves need grounding too(!) and then connect the wire that would normally go to the sender to either nothing or ground, and the needle should change.

chrisstdt · Mar 28, 2024

To test ,earth out wire in engine bay to engine block ,if wiring and gauge are OK gauge will go to top
I recently had to fit a new sender to mine

miktdish · Mar 28, 2024

drfoster said:
Hi there,

my temperature gauge on my 110 300Tdi is reading 0 even when warm, only happened in the last few days. i have disconnected the wire from the sender in the thermostat housing and put a multimeter across it from the cable to earth and its reading 12v, but when i connect the multimeter from the wire to the middle pin on the sender it reads about 8.5v , i assume it changes according to the temperature being sensed.
The circuit seems really basic so not sure whether the sender is at fault or the gauge itself. any pointers on what could be wrong and is there a good way to test the gauge itself?

cheers

Steve

The gauge is a thermistor, as it gets hotter it's resistance gets less.
There are two types for the 300tdi engine, a black and a green.
Black (AMR3321) is for the Defender and Green (AMR1425) for the Discovery.

As @chrisstdt said if you disconnect the wire at the sender and touch it onto the engine the gauge will go into the red (hot)
If it doesn't then check the connections on the back of the guage in the instrument paneland the earth on the bulkhead.

drfoster · Mar 28, 2024

great advice from everyone thanks!!, i'll give it a try as soon as the blooming rain stops!!

drfoster · Apr 4, 2024

finally managed to get time today to poke around. tried to earth the cable to get the gauge to work but it wasn't doing anything so i cut back the sender wire and put on an extension, grounded it to the engine and the temperate gauge goes all the way up so at least i know the gauge is good. fitted a new bullet receptacle connector which i had to squeeze closed a bit to make it a good snug fit on the end of the sensor.
I'll take it for a drive later and see if the gauge moves, if not then i'll get a new sensor, hopefully it was just a bad connector or bit of cable.

drfoster · Apr 4, 2024

unfortunately no dice from the gauge when on a run so it looks like a new sender is needed. I assume its easy to fit and i won't lose too much coolant when i swap it over?

chrisstdt · Apr 4, 2024

Easy enough to swap along as you can get the old one out
You'll loose very little coolant

drfoster · Apr 11, 2024

so new sensor came, black top like the old one but was a bit longer, seemed to fit okay but did lose coolant when the old one came out, not a lot, just a jet escaped probably because it was still a bit warm and under pressure. new one had an o-ring as well so its tightened up and not leaking out. old sensor was 13mm size and the new one was 12mm size on the spanner
Turning the ignition on and the temperature guage went up to where i expected it to so that all good. i'm assuming the extra length won't cause an issue to coolant flow etc.

300tdi temperature gauge

drfoster

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chrisstdt

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miktdish

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drfoster

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