S2 111S k-series temperature issues

[caz4213]

Morning all,

Had a quick search on the forums and can't find anything resembling the current issue with my Elise so I'm turning to the good people of PH in search of an answer.

Head gasket was changed on the car about 6 months ago. All was well until I did a trackday when, towards the end of the day, the temperature gauge in-car was failing to register the temperature at all (seemingly indicating the engine was running cold, despite the fact it was certainly warm as it had been running all day).

Took it out for a couple of hours a few weeks later and for the entire journey the temperature didn't register on the gauge, despite the engine being on the entire time.

Even more weirdly when I took it out again recently it had seemingly miraculously healed, with the temperature reading displaying on the gauge once it was up to operating temperature. However, every time I put my foot down the temperature reading on the gauge decreases rapidly, sometimes to the point where the reading drops off completely. As soon as I stop accelerating the temperature returns to normal again, albeit does take a minute or so.

Tried to explain the problem fairly succinctly; does anyone have any ideas for what it could potentially be? Anyone who diagnoses successfully will be fully entitled to a pint of your choice!

[400SE Dave]

Could be the temperature sender for the stack cluster, it is the blue one in the pipe close to the expansion tank if I remember right. You can them from Elise Parts etc or of course Lotus.

Other than that an airlock but would seem unlikely with the time frame you mention

I would try the Blue sensor

[Newscuttlepanel]

Thermostat stuck open? or too cool a running temp stat? Had almost exactly the same issue with my S2 Exige, Toyota engine I know but same symptoms.