D

drfoster

Well-Known Member
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
 
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.
 
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
Click to expand...

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.
 
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.
 
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?
 
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.
 
You must log in or register to reply here.

Similar threads

A
Fuel gauge and fuel light issue
Replies
4
Views
332
Acdadefender1
A
OscarBoy
300 Tdi Temperature Gauge not working, maybe?
Replies
8
Views
1K
OscarBoy
OscarBoy
D
TD5 fuel gauge not working
Replies
0
Views
290
Dandyservices
D
A
1984 109 FFR 24v oil temp gauge issues
Replies
1
Views
439
layfin
L
Naughty-Monkey
Fuel Gauge Electrical Woes...
Replies
0
Views
643
Naughty-Monkey
Naughty-Monkey