More trouble with the old thing

It won't start when cold. If I spin it over for a 30 seconds or so, it will just start and tickover at around 500 rpm for a few seconds, then dies.

After 10 minutes of doing this and probably not doing my new battery a lot of good, it ticks over, then a minute or so later I can tickle the throttle and get it to run.

It is like (I know it isn't this cos it aint got one) I am starting the car with no choke. (for younguns, this is a fuel enrichment device fitted to older cars although my mother used to pull it out to hang her handnbag on.)

I took it to one of these diagnostic centres and left it there overnight. This morning, they connected it up to the puters before trying to start it, and the computer is being told the engine is between 97C and 102C.

Ok, I know now that the engine (or coolant) temperature sender unit is faulty.

Anyone know where it is and how I can replace it?

And why does the temperature guage work correctly?

I have been told by Euro Parts that it is the green 4 pin one, but they don't know where it is.

Any thoughts anyone, as I don't want to replace it only to find that it is because I have some water under the front foot well.