V8 Temperature Gauge/Sensor

[Don Del]

I run a 1999 V8 Defender 110 Station Wagon and recently the temperature gauge has started playing up. Occasionally after getting up to operating temperature, and sometimes during warming up, the temperature gauge needle will fall back to approximately half way from the start position to the running position over a period of a couple of seconds. Then after about ten to fifteen seconds it will go back to its previous position. This fault occurs intermittently. I have an Engineguard fitted with temperature sensors on both cylinder heads and this is not displaying any change in temperature. I have bled the cooling system and checked the electrical connection to the temperature sensor.

Any suggestions about possible causes welcomed!

[Eightpot]

In order of cost of things to try- 

Clean up spade terminal on sender & make sure spade fitting is snug

Check for breaks/chaffing on the sender wire

Fit a new sender

Gauges themselves tend to be pretty reliable. 

[Don Del]

Thanks for the reply. You have summarised my thinking. I have checked and cleaned the sensor spade and the connection. The prospect of checking the sender wire does not fill me with joy but I will have to do it. As far as the sender unit is concerned I would have thought it would be either working or not working but I am only guessing, do you have any thoughts?

[Eightpot]

The sender is just a resistor, it's possible for them to fail and give variable readings as they heat up.  You could check the wire using a multimeter - a simple check would be to take the green blue wire off the back of the temp gauge, the spade off the sensor and use the continuity setting  to see if there's any earthing of the cable (one probe on the wire spade, other probe to an earth)

Or fit a temp wire from gauge to sender & see if it works any better. 

Edited February 16, 2022 by Eightpot