Disco 2 Transmission Oil temperature warning light

Hello all.
2002 TD5 owner here.
Having a very shaky time of it this afternoon.
Red light came on for the first time yesterday after 7 months.
Got the fluid checked and changed yesterday (as well as oil air and fuel filters). Drove around the block last night no probs.
Just pulled over after 20 minutes on the road and the light has come back on again, and I'm in a state of moderate anxiety about it.
I'm supposed to be doing a big drive up to Scotland on the weekend and I'm super concerned basically.
I've read a fair amount of post on here and it seems like it's hard to tell whether it's a sensor issue, but the gearbox does feel a bit off (revs aren't consistent when stationary).
I'm literally pulled over in Tesco now. Letting it cool off.
If anyone has any sound advice I would love to hear it.
A bit worried over here and feeling very under-qualified!
Thanks in advance,
Jamie

As per suggestion of another thread, I've run through the gear range with the brake down to make sure that the new fluid is throughout the transmission.

Also just to be clear. When I start the car the red light is not illuminated. Only comes on after about 15 minutes of the engine running.

Also to mention , the transmission fluid that came out of the car yesterday was dark/ filthy.

I started up again, pulled out and the temperature gauge started rising, until it went over again into the red.
Then I had to break quite sharply to not go through a red and the TC and ABS lights came on, along with the red exclamation mark, which usually indicated the handbrake is on. When it rain... ‍.
Want to cry!!!

I'd postpone your trip, or hire a car mate!
Sorry to say.

Stanleysteamer said:

I'd postpone your trip, or hire a car mate!
Sorry to say.

Click to expand...

thanks mate!

reminds me of that a novice I am!

so it turns out that I am a bigger moron than I had thought.

i asked my fiancee to read out the instructions for the red light on the temperature gauge and she instead read me the info for the wrong indicator and I simply didn't check myself to make sure.

she read the indications for the transmission oil temperature.

the problem was that the engine was simply overheating. this had never happened to me and because the gauge dropped to the bottom i thought that the red light carried a different meaning.

i am a dipstick