Water temp sender?

[targarama]

OK, driving along (or thrashing around the track) the water temp is 89-91 deg, as per usual. As soon as I come to halt (say pulling off the track into the paddock, or waiting at traffic lights after a gentle 70mph cruise) the temp goes to 98,99,100 and even up to 104 sometimes. It happens really quickly so I don't think the water temp is actually going this high. After my last track session I got a 'water temp sensor problem' on the dash which cleared and didn't come back until I parked on the drive at home (200 miles away), then restarted a few minutes later to put the car in the garage.

Fans are working fine.

It could be an airlock, I'll have a shufty, but can someone tell me where the sender unit is located? Is it otter switch stylee at the bottom of the expansion tank? (I need the sensor which feeds the dash gauge, not the fan switch).

[GreenV8S]

I have an idea that on those the fans are switched by the ECU and not by a separate otter switch. But I think you'll find one coolant temp sender for the ECU+fans and a separate one for the gauge.

[basil brush]

Both temp senders are on right hand (drivers) side of engine block. ECU sender is about half way along and dash sender is further forward.