Temperature gauge shenanigans - any suggestions?

[gatsovictim]

Hi all

Up until recently my temp gauge has been well-behaved and the needle has sat pretty much horizontal when the engine has warmed up.

However, recently it is doing something else. When at reasonable speed (60-75mph ish) the needle will go DOWN - but not consistently. It's taken to moving around in a manner not dissimilar to the petrol gauge but rather than reacting to corners it is more related to the use of the accelerator pedal.

Fearing that there wasn't enough coolant in the car, I checked it this weekend by running it for ten minutes with the cap off and could see that the coolant was expanding up the swirl tank so it looks like there's no leaks.

So - before I start suspecting the gauge itself - is there any other reason why the gauge is now doing its own thing?

Any suggestions gratefully received. I'm not hugely mechanical so please bear with me.

TTFN

[phillpot]

Take a look back a few threads to one from "Lukas" titled Temperature gauge not working. Could be a dodgey electrical connection to the sender unit ( dodgey electrics on a TVR ? Never )
Could be the gauge but I'd have thought unlikely, they're usually pretty reliable and only do what they are told !

One other thought, is fan belt ok ? If belt slipping could create fluctuating voltage to gauge ? is volt meter also swinging around ?

HTH

[Jed-S]

gatsovictim said:

Fearing that there wasn't enough coolant in the car, I checked it this weekend by running it for ten minutes with the cap off and could see that the coolant was expanding up the swirl tank so it looks like there's no leaks.

The swirlpot should be full when cold. If it isn't then replace the pressure cap (not forgetting the rubber seal it will need), top up the coolant and then try again. If you compare the height of the water with the level of the temperature sender then you'll see that it doesn't take much of a drop in water level to leave the sender potentially out of the water.